Thyroid Gland: A highly vascularized endocrine gland consisting of two lobes joined by a thin band of tissue with one lobe on each side of the TRACHEA. It secretes THYROID HORMONES from the follicular cells and CALCITONIN from the parafollicular cells thereby regulating METABOLISM and CALCIUM level in blood, respectively.Thyroid Neoplasms: Tumors or cancer of the THYROID GLAND.Immunoglobulins: Multi-subunit proteins which function in IMMUNITY. They are produced by B LYMPHOCYTES from the IMMUNOGLOBULIN GENES. They are comprised of two heavy (IMMUNOGLOBULIN HEAVY CHAINS) and two light chains (IMMUNOGLOBULIN LIGHT CHAINS) with additional ancillary polypeptide chains depending on their isoforms. The variety of isoforms include monomeric or polymeric forms, and transmembrane forms (B-CELL ANTIGEN RECEPTORS) or secreted forms (ANTIBODIES). They are divided by the amino acid sequence of their heavy chains into five classes (IMMUNOGLOBULIN A; IMMUNOGLOBULIN D; IMMUNOGLOBULIN E; IMMUNOGLOBULIN G; IMMUNOGLOBULIN M) and various subclasses.Immunoglobulin G: The major immunoglobulin isotype class in normal human serum. There are several isotype subclasses of IgG, for example, IgG1, IgG2A, and IgG2B.Thyroid Hormones: Natural hormones secreted by the THYROID GLAND, such as THYROXINE, and their synthetic analogs.Thyroid Diseases: Pathological processes involving the THYROID GLAND.Immunoglobulin A: Represents 15-20% of the human serum immunoglobulins, mostly as the 4-chain polymer in humans or dimer in other mammals. Secretory IgA (IMMUNOGLOBULIN A, SECRETORY) is the main immunoglobulin in secretions.Immunoglobulin M: A class of immunoglobulin bearing mu chains (IMMUNOGLOBULIN MU-CHAINS). IgM can fix COMPLEMENT. The name comes from its high molecular weight and originally being called a macroglobulin.Thyroid Nodule: A small circumscribed mass in the THYROID GLAND that can be of neoplastic growth or non-neoplastic abnormality. It lacks a well-defined capsule or glandular architecture. Thyroid nodules are often benign but can be malignant. The growth of nodules can lead to a multinodular goiter (GOITER, NODULAR).Immunoglobulin Heavy Chains: The largest of polypeptide chains comprising immunoglobulins. They contain 450 to 600 amino acid residues per chain, and have molecular weights of 51-72 kDa.Immunoglobulins, Intravenous: Immunoglobulin preparations used in intravenous infusion, containing primarily IMMUNOGLOBULIN G. They are used to treat a variety of diseases associated with decreased or abnormal immunoglobulin levels including pediatric AIDS; primary HYPERGAMMAGLOBULINEMIA; SCID; CYTOMEGALOVIRUS infections in transplant recipients, LYMPHOCYTIC LEUKEMIA, CHRONIC; Kawasaki syndrome, infection in neonates, and IDIOPATHIC THROMBOCYTOPENIC PURPURA.Genes, Immunoglobulin: Genes encoding the different subunits of the IMMUNOGLOBULINS, for example the IMMUNOGLOBULIN LIGHT CHAIN GENES and the IMMUNOGLOBULIN HEAVY CHAIN GENES. The heavy and light immunoglobulin genes are present as gene segments in the germline cells. The completed genes are created when the segments are shuffled and assembled (B-LYMPHOCYTE GENE REARRANGEMENT) during B-LYMPHOCYTE maturation. The gene segments of the human light and heavy chain germline genes are symbolized V (variable), J (joining) and C (constant). The heavy chain germline genes have an additional segment D (diversity).Immunoglobulin Light Chains: Polypeptide chains, consisting of 211 to 217 amino acid residues and having a molecular weight of approximately 22 kDa. There are two major types of light chains, kappa and lambda. Two Ig light chains and two Ig heavy chains (IMMUNOGLOBULIN HEAVY CHAINS) make one immunoglobulin molecule.Thyroid Function Tests: Blood tests used to evaluate the functioning of the thyroid gland.Receptors, Thyroid Hormone: Specific high affinity binding proteins for THYROID HORMONES in target cells. They are usually found in the nucleus and regulate DNA transcription. These receptors are activated by hormones that leads to transcription, cell differentiation, and growth suppression. Thyroid hormone receptors are encoded by two genes (GENES, ERBA): erbA-alpha and erbA-beta for alpha and beta thyroid hormone receptors, respectively.Immunoglobulin kappa-Chains: One of the types of light chains of the immunoglobulins with a molecular weight of approximately 22 kDa.Immunoglobulin E: An immunoglobulin associated with MAST CELLS. Overexpression has been associated with allergic hypersensitivity (HYPERSENSITIVITY, IMMEDIATE).Thyrotropin: A glycoprotein hormone secreted by the adenohypophysis (PITUITARY GLAND, ANTERIOR). Thyrotropin stimulates THYROID GLAND by increasing the iodide transport, synthesis and release of thyroid hormones (THYROXINE and TRIIODOTHYRONINE). Thyrotropin consists of two noncovalently linked subunits, alpha and beta. Within a species, the alpha subunit is common in the pituitary glycoprotein hormones (TSH; LUTEINIZING HORMONE and FSH), but the beta subunit is unique and confers its biological specificity.Immunoglobulin A, Secretory: The principle immunoglobulin in exocrine secretions such as milk, respiratory and intestinal mucin, saliva and tears. The complete molecule (around 400 kD) is composed of two four-chain units of IMMUNOGLOBULIN A, one SECRETORY COMPONENT and one J chain (IMMUNOGLOBULIN J-CHAINS).Triiodothyronine: A T3 thyroid hormone normally synthesized and secreted by the thyroid gland in much smaller quantities than thyroxine (T4). Most T3 is derived from peripheral monodeiodination of T4 at the 5' position of the outer ring of the iodothyronine nucleus. The hormone finally delivered and used by the tissues is mainly T3.Immunoglobulin Variable Region: That region of the immunoglobulin molecule that varies in its amino acid sequence and composition, and comprises the binding site for a specific antigen. It is located at the N-terminus of the Fab fragment of the immunoglobulin. It includes hypervariable regions (COMPLEMENTARITY DETERMINING REGIONS) and framework regions.Thyroxine: The major hormone derived from the thyroid gland. Thyroxine is synthesized via the iodination of tyrosines (MONOIODOTYROSINE) and the coupling of iodotyrosines (DIIODOTYROSINE) in the THYROGLOBULIN. Thyroxine is released from thyroglobulin by proteolysis and secreted into the blood. Thyroxine is peripherally deiodinated to form TRIIODOTHYRONINE which exerts a broad spectrum of stimulatory effects on cell metabolism.Immunoglobulin mu-Chains: The class of heavy chains found in IMMUNOGLOBULIN M. They have a molecular weight of approximately 72 kDa and they contain about 57 amino acid residues arranged in five domains and have more oligosaccharide branches and a higher carbohydrate content than the heavy chains of IMMUNOGLOBULIN G.Hypothyroidism: A syndrome that results from abnormally low secretion of THYROID HORMONES from the THYROID GLAND, leading to a decrease in BASAL METABOLIC RATE. In its most severe form, there is accumulation of MUCOPOLYSACCHARIDES in the SKIN and EDEMA, known as MYXEDEMA.Immunoglobulin Isotypes: The classes of immunoglobulins found in any species of animal. In man there are nine classes that migrate in five different groups in electrophoresis; they each consist of two light and two heavy protein chains, and each group has distinguishing structural and functional properties.Immunoglobulin lambda-Chains: One of the types of light chain subunits of the immunoglobulins with a molecular weight of approximately 22 kDa.ThyroglobulinCarcinoma, Papillary: A malignant neoplasm characterized by the formation of numerous, irregular, finger-like projections of fibrous stroma that is covered with a surface layer of neoplastic epithelial cells. (Stedman, 25th ed)Adenocarcinoma, Follicular: An adenocarcinoma of the thyroid gland, in which the cells are arranged in the form of follicles. (From Dorland, 27th ed)Immunoglobulin D: An immunoglobulin which accounts for less than 1% of plasma immunoglobulin. It is found on the membrane of many circulating B LYMPHOCYTES.Thyroidectomy: Surgical removal of the thyroid gland. (Dorland, 28th ed)Iodide Peroxidase: A hemeprotein that catalyzes the oxidation of the iodide radical to iodine with the subsequent iodination of many organic compounds, particularly proteins. EC Constant Regions: The domains of the immunoglobulin molecules that are invariable in their amino acid sequence within any class or subclass of immunoglobulin. They confer biological as well as structural functions to immunoglobulins. One each on both the light chains and the heavy chains comprises the C-terminus half of the IMMUNOGLOBULIN FAB FRAGMENT and two or three of them make up the rest of the heavy chains (all of the IMMUNOGLOBULIN FC FRAGMENT)Immunoglobulin Fc Fragments: Crystallizable fragments composed of the carboxy-terminal halves of both IMMUNOGLOBULIN HEAVY CHAINS linked to each other by disulfide bonds. Fc fragments contain the carboxy-terminal parts of the heavy chain constant regions that are responsible for the effector functions of an immunoglobulin (COMPLEMENT fixation, binding to the cell membrane via FC RECEPTORS, and placental transport). This fragment can be obtained by digestion of immunoglobulins with the proteolytic enzyme PAPAIN.B-Lymphocytes: Lymphoid cells concerned with humoral immunity. They are short-lived cells resembling bursa-derived lymphocytes of birds in their production of immunoglobulin upon appropriate stimulation.Thyroid Hormone Receptors beta: High affinity receptors for THYROID HORMONES, especially TRIIODOTHYRONINE. These receptors are usually found in the nucleus where they regulate DNA transcription. They are encoded by the THRB gene (also known as NR1A2, THRB1, or ERBA2 gene) as several isoforms produced by alternative splicing. Mutations in the THRB gene cause THYROID HORMONE RESISTANCE SYNDROME.Hyperthyroidism: Hypersecretion of THYROID HORMONES from the THYROID GLAND. Elevated levels of thyroid hormones increase BASAL METABOLIC RATE.Goiter: Enlargement of the THYROID GLAND that may increase from about 20 grams to hundreds of grams in human adults. Goiter is observed in individuals with normal thyroid function (euthyroidism), thyroid deficiency (HYPOTHYROIDISM), or hormone overproduction (HYPERTHYROIDISM). Goiter may be congenital or acquired, sporadic or endemic (GOITER, ENDEMIC).Immunoglobulin Class Switching: Gene rearrangement of the B-lymphocyte which results in a substitution in the type of heavy-chain constant region that is expressed. This allows the effector response to change while the antigen binding specificity (variable region) remains the same. The majority of class switching occurs by a DNA recombination event but it also can take place at the level of RNA processing.Immunoglobulin gamma-Chains: Heavy chains of IMMUNOGLOBULIN G having a molecular weight of approximately 51 kDa. They contain about 450 amino acid residues arranged in four domains and an oligosaccharide component covalently bound to the Fc fragment constant region. The gamma heavy chain subclasses (for example, gamma 1, gamma 2a, and gamma 2b) of the IMMUNOGLOBULIN G isotype subclasses (IgG1, IgG2A, and IgG2B) resemble each other more closely than the heavy chains of the other IMMUNOGLOBULIN ISOTYPES.Immunoglobulin Fab Fragments: Univalent antigen-binding fragments composed of one entire IMMUNOGLOBULIN LIGHT CHAIN and the amino terminal end of one of the IMMUNOGLOBULIN HEAVY CHAINS from the hinge region, linked to each other by disulfide bonds. Fab contains the IMMUNOGLOBULIN VARIABLE REGIONS, which are part of the antigen-binding site, and the first IMMUNOGLOBULIN CONSTANT REGIONS. This fragment can be obtained by digestion of immunoglobulins with the proteolytic enzyme PAPAIN.Immunoglobulin J-Chains: A 15 kD "joining" peptide that forms one of the linkages between monomers of IMMUNOGLOBULIN A or IMMUNOGLOBULIN M in the formation of polymeric immunoglobulins. There is one J chain per one IgA dimer or one IgM pentamer. It is also involved in binding the polymeric immunoglobulins to POLYMERIC IMMUNOGLOBULIN RECEPTOR which is necessary for their transcytosis to the lumen. It is distinguished from the IMMUNOGLOBULIN JOINING REGION which is part of the IMMUNOGLOBULIN VARIABLE REGION of the immunoglobulin light and heavy chains.Iodine: A nonmetallic element of the halogen group that is represented by the atomic symbol I, atomic number 53, and atomic weight of 126.90. It is a nutritionally essential element, especially important in thyroid hormone synthesis. In solution, it has anti-infective properties and is used topically.Thyroiditis, Autoimmune: Inflammatory disease of the THYROID GLAND due to autoimmune responses leading to lymphocytic infiltration of the gland. It is characterized by the presence of circulating thyroid antigen-specific T-CELLS and thyroid AUTOANTIBODIES. The clinical signs can range from HYPOTHYROIDISM to THYROTOXICOSIS depending on the type of autoimmune thyroiditis.Graves Disease: A common form of hyperthyroidism with a diffuse hyperplastic GOITER. It is an autoimmune disorder that produces antibodies against the THYROID STIMULATING HORMONE RECEPTOR. These autoantibodies activate the TSH receptor, thereby stimulating the THYROID GLAND and hypersecretion of THYROID HORMONES. These autoantibodies can also affect the eyes (GRAVES OPHTHALMOPATHY) and the skin (Graves dermopathy).Immunoglobulin Allotypes: Allelic variants of the immunoglobulin light chains (IMMUNOGLOBULIN LIGHT CHAINS) or heavy chains (IMMUNOGLOBULIN HEAVY CHAINS) encoded by ALLELES of IMMUNOGLOBULIN GENES.Immunoglobulin Fragments: Partial immunoglobulin molecules resulting from selective cleavage by proteolytic enzymes or generated through PROTEIN ENGINEERING techniques.Receptors, Polymeric Immunoglobulin: Specialized Fc receptors (RECEPTORS, FC) for polymeric immunoglobulins, which mediate transcytosis of polymeric IMMUNOGLOBULIN A and IMMUNOGLOBULIN M into external secretions. They are found on the surfaces of epithelial cells and hepatocytes. After binding to IMMUNOGLOBULIN A, the receptor-ligand complex undergoes endocytosis, transport by vesicle, and secretion into the lumen by exocytosis. Before release, the part of the receptor (SECRETORY COMPONENT) that is bound to IMMUNOGLOBULIN A is proteolytically cleaved from its transmembrane tail. (From Rosen et al., The Dictionary of Immunology, 1989)Iodine Radioisotopes: Unstable isotopes of iodine that decay or disintegrate emitting radiation. I atoms with atomic weights 117-139, except I 127, are radioactive iodine isotopes.Antibodies, Bacterial: Immunoglobulins produced in a response to BACTERIAL ANTIGENS.Immunoglobulin Joining Region: A segment of the immunoglobulin heavy chains, encoded by the IMMUNOGLOBULIN HEAVY CHAIN GENES in the J segment where, during the maturation of B-LYMPHOCYTES; the gene segment for the variable region upstream is joined to a constant region gene segment downstream. The exact position of joining of the two gene segments is variable and contributes to ANTIBODY DIVERSITY. It is distinguished from the IMMUNOGLOBULIN J CHAINS; a separate polypeptide that serves as a linkage piece in polymeric IGA or IGM.Thyroid Hormone Receptors alpha: High affinity receptors for THYROID HORMONES, especially TRIIODOTHYRONINE. These receptors are usually found in the nucleus where they regulate DNA transcription. They are encoded by the THRA gene (also known as NR1A1, THRA1, ERBA or ERBA1 gene) as several isoforms produced by alternative splicing.Enzyme-Linked Immunosorbent Assay: An immunoassay utilizing an antibody labeled with an enzyme marker such as horseradish peroxidase. While either the enzyme or the antibody is bound to an immunosorbent substrate, they both retain their biologic activity; the change in enzyme activity as a result of the enzyme-antibody-antigen reaction is proportional to the concentration of the antigen and can be measured spectrophotometrically or with the naked eye. Many variations of the method have been developed.Molecular Sequence Data: Descriptions of specific amino acid, carbohydrate, or nucleotide sequences which have appeared in the published literature and/or are deposited in and maintained by databanks such as GENBANK, European Molecular Biology Laboratory (EMBL), National Biomedical Research Foundation (NBRF), or other sequence repositories.Autoantibodies: Antibodies that react with self-antigens (AUTOANTIGENS) of the organism that produced them.Antibody Specificity: The property of antibodies which enables them to react with some ANTIGENIC DETERMINANTS and not with others. Specificity is dependent on chemical composition, physical forces, and molecular structure at the binding site.Receptors, Antigen, B-Cell: IMMUNOGLOBULINS on the surface of B-LYMPHOCYTES. Their MESSENGER RNA contains an EXON with a membrane spanning sequence, producing immunoglobulins in the form of type I transmembrane proteins as opposed to secreted immunoglobulins (ANTIBODIES) which do not contain the membrane spanning segment.Myeloma Proteins: Abnormal immunoglobulins characteristic of MULTIPLE MYELOMA.Goiter, Nodular: An enlarged THYROID GLAND containing multiple nodules (THYROID NODULE), usually resulting from recurrent thyroid HYPERPLASIA and involution over many years to produce the irregular enlargement. Multinodular goiters may be nontoxic or may induce THYROTOXICOSIS.Receptors, Thyrotropin: Cell surface proteins that bind pituitary THYROTROPIN (also named thyroid stimulating hormone or TSH) and trigger intracellular changes of the target cells. TSH receptors are present in the nervous system and on target cells in the thyroid gland. Autoantibodies to TSH receptors are implicated in thyroid diseases such as GRAVES DISEASE and Hashimoto disease (THYROIDITIS, AUTOIMMUNE).Base Sequence: The sequence of PURINES and PYRIMIDINES in nucleic acids and polynucleotides. It is also called nucleotide sequence.Carcinoma, Papillary, Follicular: A thyroid neoplasm of mixed papillary and follicular arrangement. Its biological behavior and prognosis is the same as that of a papillary adenocarcinoma of the thyroid. (From DeVita Jr et al., Cancer: Principles & Practice of Oncology, 3d ed, p1271)Carcinoma, Medullary: A carcinoma composed mainly of epithelial elements with little or no stroma. Medullary carcinomas of the breast constitute 5%-7% of all mammary carcinomas; medullary carcinomas of the thyroid comprise 3%-10% of all thyroid malignancies. (From Dorland, 27th ed; DeVita Jr et al., Cancer: Principles & Practice of Oncology, 3d ed, p1141; Segen, Dictionary of Modern Medicine, 1992)Genes, Immunoglobulin Heavy Chain: Genes and gene segments encoding the IMMUNOGLOBULIN HEAVY CHAINS. Gene segments of the heavy chain genes are symbolized V (variable), D (diversity), J (joining), and C (constant).Somatic Hypermutation, Immunoglobulin: A programmed mutation process whereby changes are introduced to the nucleotide sequence of immunoglobulin gene DNA during development.Antithyroid Agents: Agents that are used to treat hyperthyroidism by reducing the excessive production of thyroid hormones.Immunoglobulins, Thyroid-Stimulating: Autoantibodies that bind to the thyroid-stimulating hormone (TSH) receptor (RECEPTORS, THYROTROPIN) on thyroid epithelial cells. The autoantibodies mimic TSH causing an unregulated production of thyroid hormones characteristic of GRAVES DISEASE.Thyroiditis: Inflammatory diseases of the THYROID GLAND. Thyroiditis can be classified into acute (THYROIDITIS, SUPPURATIVE), subacute (granulomatous and lymphocytic), chronic fibrous (Riedel's), chronic lymphocytic (HASHIMOTO DISEASE), transient (POSTPARTUM THYROIDITIS), and other AUTOIMMUNE THYROIDITIS subtypes.Thyroid Crisis: A dangerous life-threatening hypermetabolic condition characterized by high FEVER and dysfunction of the cardiovascular, the nervous, and the gastrointestinal systems.Plasmacytoma: Any discrete, presumably solitary, mass of neoplastic PLASMA CELLS either in BONE MARROW or various extramedullary sites.Immunoglobulin delta-Chains: The class of heavy chains found in IMMUNOGLOBULIN D. They have a molecular weight of approximately 64 kDa and they contain about 500 amino acid residues arranged in four domains and an oligosaccharide component covalently bound to the Fc fragment constant region.Immunoglobulin Switch Region: A site located in the INTRONS at the 5' end of each constant region segment of a immunoglobulin heavy-chain gene where recombination (or rearrangement) occur during IMMUNOGLOBULIN CLASS SWITCHING. Ig switch regions are found on genes encoding all five classes (IMMUNOGLOBULIN ISOTYPES) of IMMUNOGLOBULIN HEAVY CHAINS.Antibodies, Anti-Idiotypic: Antibodies which react with the individual structural determinants (idiotopes) on the variable region of other antibodies.Immunoglobulin alpha-Chains: The class of heavy chains found in IMMUNOGLOBULIN A. They have a molecular weight of approximately 58 kDa and contain about 470 amino acid residues arranged in four domains and an oligosaccharide component bound covalently to their Fc fragment constant region.Iodides: Inorganic binary compounds of iodine or the I- ion.Antibodies, Monoclonal: Antibodies produced by a single clone of cells.Immunoglobulin Idiotypes: Unique genetically-controlled determinants present on ANTIBODIES whose specificity is limited to a single group of proteins (e.g., another antibody molecule or an individual myeloma protein). The idiotype appears to represent the antigenicity of the antigen-binding site of the antibody and to be genetically codetermined with it. The idiotypic determinants have been precisely located to the IMMUNOGLOBULIN VARIABLE REGION of both immunoglobin polypeptide chains.gamma-Globulins: Serum globulins that migrate to the gamma region (most positively charged) upon ELECTROPHORESIS. At one time, gamma-globulins came to be used as a synonym for immunoglobulins since most immunoglobulins are gamma globulins and conversely most gamma globulins are immunoglobulins. But since some immunoglobulins exhibit an alpha or beta electrophoretic mobility, that usage is in decline.Antibodies, Viral: Immunoglobulins produced in response to VIRAL ANTIGENS.Propylthiouracil: A thiourea antithyroid agent. Propythiouracil inhibits the synthesis of thyroxine and inhibits the peripheral conversion of throxine to tri-iodothyronine. It is used in the treatment of hyperthyroidism. (From Martindale, The Extra Pharmacopeoia, 30th ed, p534)Thyroid Hormone Resistance Syndrome: An inherited autosomal recessive trait, characterized by peripheral resistance to THYROID HORMONES and the resulting elevation in serum levels of THYROXINE and TRIIODOTHYRONINE. This syndrome is caused by mutations of gene THRB encoding the THYROID HORMONE RECEPTORS BETA in target cells. HYPOTHYROIDISM in these patients is partly overcome by the increased thyroid hormone levels.Secretory Component: The extracellular moiety of the POLYMERIC IMMUNOGLOBULIN RECEPTOR found alone or complexed with IGA or IGM, in a variety of external secretions (tears, bile, colostrum.) Secretory component is derived by proteolytic cleavage of the receptor during transcytosis. When immunoglobulins IgA and IgM are bound to the receptor, during their transcytosis secretory component becomes covalently attached to them generating SECRETORY IMMUNOGLOBULIN A or secretory IMMUNOGLOBULIN M.Antibody Formation: The production of ANTIBODIES by proliferating and differentiated B-LYMPHOCYTES under stimulation by ANTIGENS.Biopsy, Fine-Needle: Using fine needles (finer than 22-gauge) to remove tissue or fluid specimens from the living body for examination in the pathology laboratory and for disease diagnosis.Hashimoto Disease: Chronic autoimmune thyroiditis, characterized by the presence of high serum thyroid AUTOANTIBODIES; GOITER; and HYPOTHYROIDISM.Carcinoma: A malignant neoplasm made up of epithelial cells tending to infiltrate the surrounding tissues and give rise to metastases. It is a histological type of neoplasm but is often wrongly used as a synonym for "cancer." (From Dorland, 27th ed)Agammaglobulinemia: An immunologic deficiency state characterized by an extremely low level of generally all classes of gamma-globulin in the blood.Immunoglobulin Gm Allotypes: Allelic variants of the gamma-immunoglobulin heavy chain (IMMUNOGLOBULIN GAMMA-CHAINS) encoded by ALLELES of IMMUNOGLOBULIN HEAVY CHAIN GENES.Cell Line: Established cell cultures that have the potential to propagate indefinitely.Mice, Inbred BALB CMethimazole: A thioureylene antithyroid agent that inhibits the formation of thyroid hormones by interfering with the incorporation of iodine into tyrosyl residues of thyroglobulin. This is done by interfering with the oxidation of iodide ion and iodotyrosyl groups through inhibition of the peroxidase enzyme.Colostrum: The thin, yellow, serous fluid secreted by the mammary glands during pregnancy and immediately postpartum before lactation begins. It consists of immunologically active substances, white blood cells, water, protein, fat, and carbohydrates.Immunization, Passive: Transfer of immunity from immunized to non-immune host by administration of serum antibodies, or transplantation of lymphocytes (ADOPTIVE TRANSFER).Receptors, Fc: Molecules found on the surface of some, but not all, B-lymphocytes, T-lymphocytes, and macrophages, which recognize and combine with the Fc (crystallizable) portion of immunoglobulin molecules.Binding Sites, Antibody: Local surface sites on antibodies which react with antigen determinant sites on antigens (EPITOPES.) They are formed from parts of the variable regions of FAB FRAGMENTS.Antigen-Antibody Complex: The complex formed by the binding of antigen and antibody molecules. The deposition of large antigen-antibody complexes leading to tissue damage causes IMMUNE COMPLEX DISEASES.Triiodothyronine, Reverse: A metabolite of THYROXINE, formed by the peripheral enzymatic monodeiodination of T4 at the 5 position of the inner ring of the iodothyronine nucleus.Immunoelectrophoresis: A technique that combines protein electrophoresis and double immunodiffusion. In this procedure proteins are first separated by gel electrophoresis (usually agarose), then made visible by immunodiffusion of specific antibodies. A distinct elliptical precipitin arc results for each protein detectable by the antisera.Fluorescent Antibody Technique: Test for tissue antigen using either a direct method, by conjugation of antibody with fluorescent dye (FLUORESCENT ANTIBODY TECHNIQUE, DIRECT) or an indirect method, by formation of antigen-antibody complex which is then labeled with fluorescein-conjugated anti-immunoglobulin antibody (FLUORESCENT ANTIBODY TECHNIQUE, INDIRECT). The tissue is then examined by fluorescence microscopy.Gene Rearrangement: The ordered rearrangement of gene regions by DNA recombination such as that which occurs normally during development.Gene Rearrangement, B-Lymphocyte, Heavy Chain: Ordered rearrangement of B-lymphocyte variable gene regions of the IMMUNOGLOBULIN HEAVY CHAINS, thereby contributing to antibody diversity. It occurs during the first stage of differentiation of the IMMATURE B-LYMPHOCYTES.Thyrotoxicosis: A hypermetabolic syndrome caused by excess THYROID HORMONES which may come from endogenous or exogenous sources. The endogenous source of hormone may be thyroid HYPERPLASIA; THYROID NEOPLASMS; or hormone-producing extrathyroidal tissue. Thyrotoxicosis is characterized by NERVOUSNESS; TACHYCARDIA; FATIGUE; WEIGHT LOSS; heat intolerance; and excessive SWEATING.Gene Rearrangement, B-Lymphocyte: Ordered rearrangement of B-lymphocyte variable gene regions coding for the IMMUNOGLOBULIN CHAINS, thereby contributing to antibody diversity. It occurs during the differentiation of the IMMATURE B-LYMPHOCYTES.Amino Acid Sequence: The order of amino acids as they occur in a polypeptide chain. This is referred to as the primary structure of proteins. It is of fundamental importance in determining PROTEIN CONFORMATION.Antibodies: Immunoglobulin molecules having a specific amino acid sequence by virtue of which they interact only with the ANTIGEN (or a very similar shape) that induced their synthesis in cells of the lymphoid series (especially PLASMA CELLS).RNA, Messenger: RNA sequences that serve as templates for protein synthesis. Bacterial mRNAs are generally primary transcripts in that they do not require post-transcriptional processing. Eukaryotic mRNA is synthesized in the nucleus and must be exported to the cytoplasm for translation. Most eukaryotic mRNAs have a sequence of polyadenylic acid at the 3' end, referred to as the poly(A) tail. The function of this tail is not known for certain, but it may play a role in the export of mature mRNA from the nucleus as well as in helping stabilize some mRNA molecules by retarding their degradation in the cytoplasm.Immune Sera: Serum that contains antibodies. It is obtained from an animal that has been immunized either by ANTIGEN injection or infection with microorganisms containing the antigen.Staphylococcal Protein A: A protein present in the cell wall of most Staphylococcus aureus strains. The protein selectively binds to the Fc region of human normal and myeloma-derived IMMUNOGLOBULIN G. It elicits antibody activity and may cause hypersensitivity reactions due to histamine release; has also been used as cell surface antigen marker and in the clinical assessment of B lymphocyte function.Lymphocytes: White blood cells formed in the body's lymphoid tissue. The nucleus is round or ovoid with coarse, irregularly clumped chromatin while the cytoplasm is typically pale blue with azurophilic (if any) granules. Most lymphocytes can be classified as either T or B (with subpopulations of each), or NATURAL KILLER CELLS.Congenital Hypothyroidism: A condition in infancy or early childhood due to an in-utero deficiency of THYROID HORMONES that can be caused by genetic or environmental factors, such as thyroid dysgenesis or HYPOTHYROIDISM in infants of mothers treated with THIOURACIL during pregnancy. Endemic cretinism is the result of iodine deficiency. Clinical symptoms include severe MENTAL RETARDATION, impaired skeletal development, short stature, and MYXEDEMA.Spleen: An encapsulated lymphatic organ through which venous blood filters.Thyroid Cartilage: The largest cartilage of the larynx consisting of two laminae fusing anteriorly at an acute angle in the midline of the neck. The point of fusion forms a subcutaneous projection known as the Adam's apple.Rabbits: The species Oryctolagus cuniculus, in the family Leporidae, order LAGOMORPHA. Rabbits are born in burrows, furless, and with eyes and ears closed. In contrast with HARES, rabbits have 22 chromosome pairs.Immunoenzyme Techniques: Immunologic techniques based on the use of: (1) enzyme-antibody conjugates; (2) enzyme-antigen conjugates; (3) antienzyme antibody followed by its homologous enzyme; or (4) enzyme-antienzyme complexes. These are used histologically for visualizing or labeling tissue specimens.Chernobyl Nuclear Accident: April 25th -26th, 1986 nuclear power accident that occurred at Chernobyl in the former USSR (Ukraine) located 80 miles north of Kiev.Plasma Cells: Specialized forms of antibody-producing B-LYMPHOCYTES. They synthesize and secrete immunoglobulin. They are found only in lymphoid organs and at sites of immune responses and normally do not circulate in the blood or lymph. (Rosen et al., Dictionary of Immunology, 1989, p169 & Abbas et al., Cellular and Molecular Immunology, 2d ed, p20)Adenocarcinoma, Papillary: An adenocarcinoma containing finger-like processes of vascular connective tissue covered by neoplastic epithelium, projecting into cysts or the cavity of glands or follicles. It occurs most frequently in the ovary and thyroid gland. (Stedman, 25th ed)Long-Acting Thyroid Stimulator: An immunoglobulin G, often found in the blood of hyperthyroid individuals. It stimulates the thyroid for a longer duration than does thyrotoxin and may cause hyperthyroidism in newborns due to placental transmission.Proto-Oncogene Proteins c-ret: Receptor protein-tyrosine kinases involved in the signaling of GLIAL CELL-LINE DERIVED NEUROTROPHIC FACTOR ligands. They contain an extracellular cadherin domain and form a receptor complexes with GDNF RECEPTORS. Mutations in ret protein are responsible for HIRSCHSPRUNG DISEASE and MULTIPLE ENDOCRINE NEOPLASIA TYPE 2.Immunodiffusion: Technique involving the diffusion of antigen or antibody through a semisolid medium, usually agar or agarose gel, with the result being a precipitin reaction.Mutation: Any detectable and heritable change in the genetic material that causes a change in the GENOTYPE and which is transmitted to daughter cells and to succeeding generations.Immunization: Deliberate stimulation of the host's immune response. ACTIVE IMMUNIZATION involves administration of ANTIGENS or IMMUNOLOGIC ADJUVANTS. PASSIVE IMMUNIZATION involves administration of IMMUNE SERA or LYMPHOCYTES or their extracts (e.g., transfer factor, immune RNA) or transplantation of immunocompetent cell producing tissue (thymus or bone marrow).T-Lymphocytes: Lymphocytes responsible for cell-mediated immunity. Two types have been identified - cytotoxic (T-LYMPHOCYTES, CYTOTOXIC) and helper T-lymphocytes (T-LYMPHOCYTES, HELPER-INDUCER). They are formed when lymphocytes circulate through the THYMUS GLAND and differentiate to thymocytes. When exposed to an antigen, they divide rapidly and produce large numbers of new T cells sensitized to that antigen.Adenoma: A benign epithelial tumor with a glandular organization.Hybridomas: Cells artificially created by fusion of activated lymphocytes with neoplastic cells. The resulting hybrid cells are cloned and produce pure MONOCLONAL ANTIBODIES or T-cell products, identical to those produced by the immunologically competent parent cell.Time Factors: Elements of limited time intervals, contributing to particular results or situations.Genes, Immunoglobulin Light Chain: Genes and gene segments encoding the IMMUNOGLOBULIN LIGHT CHAINS. Gene segments of the light chain genes are designated as V (variable), J (joining), and C (constant).Immunoglobulin epsilon-Chains: The class of heavy chains found in IMMUNOGLOBULIN E. They have a molecular weight of approximately 72 kDa and they contain about 550 amino acid residues arranged in five domains and about three times more carbohydrate than the heavy chains of IMMUNOGLOBULIN A; IMMUNOGLOBULIN D; and IMMUNOGLOBULIN G.Sensitivity and Specificity: Binary classification measures to assess test results. Sensitivity or recall rate is the proportion of true positives. Specificity is the probability of correctly determining the absence of a condition. (From Last, Dictionary of Epidemiology, 2d ed)Cross Reactions: Serological reactions in which an antiserum against one antigen reacts with a non-identical but closely related antigen.Autoimmune Diseases: Disorders that are characterized by the production of antibodies that react with host tissues or immune effector cells that are autoreactive to endogenous peptides.Epitopes: Sites on an antigen that interact with specific antibodies.DNA: A deoxyribonucleotide polymer that is the primary genetic material of all cells. Eukaryotic and prokaryotic organisms normally contain DNA in a double-stranded state, yet several important biological processes transiently involve single-stranded regions. DNA, which consists of a polysugar-phosphate backbone possessing projections of purines (adenine and guanine) and pyrimidines (thymine and cytosine), forms a double helix that is held together by hydrogen bonds between these purines and pyrimidines (adenine to thymine and guanine to cytosine).Antigen-Antibody Reactions: The processes triggered by interactions of ANTIBODIES with their ANTIGENS.Gene Rearrangement, B-Lymphocyte, Light Chain: Ordered rearrangement of B-lymphocyte variable gene regions coding for the kappa or lambda IMMUNOGLOBULIN LIGHT CHAINS, thereby contributing to antibody diversity. It occurs during the second stage of differentiation of the IMMATURE B-LYMPHOCYTES.Pokeweed Mitogens: Proteins isolated from the roots of the pokeweed, Phytolacca americana, that agglutinate some erythrocytes, stimulate mitosis and antibody synthesis in lymphocytes, and induce activation of plasma cells.Immunologic Deficiency Syndromes: Syndromes in which there is a deficiency or defect in the mechanisms of immunity, either cellular or humoral.Radioimmunoassay: Classic quantitative assay for detection of antigen-antibody reactions using a radioactively labeled substance (radioligand) either directly or indirectly to measure the binding of the unlabeled substance to a specific antibody or other receptor system. Non-immunogenic substances (e.g., haptens) can be measured if coupled to larger carrier proteins (e.g., bovine gamma-globulin or human serum albumin) capable of inducing antibody formation.Antigens, Bacterial: Substances elaborated by bacteria that have antigenic activity.IgA Deficiency: A dysgammaglobulinemia characterized by a deficiency of IMMUNOGLOBULIN A.Complement System Proteins: Serum glycoproteins participating in the host defense mechanism of COMPLEMENT ACTIVATION that creates the COMPLEMENT MEMBRANE ATTACK COMPLEX. Included are glycoproteins in the various pathways of complement activation (CLASSICAL COMPLEMENT PATHWAY; ALTERNATIVE COMPLEMENT PATHWAY; and LECTIN COMPLEMENT PATHWAY).Polymerase Chain Reaction: In vitro method for producing large amounts of specific DNA or RNA fragments of defined length and sequence from small amounts of short oligonucleotide flanking sequences (primers). The essential steps include thermal denaturation of the double-stranded target molecules, annealing of the primers to their complementary sequences, and extension of the annealed primers by enzymatic synthesis with DNA polymerase. The reaction is efficient, specific, and extremely sensitive. Uses for the reaction include disease diagnosis, detection of difficult-to-isolate pathogens, mutation analysis, genetic testing, DNA sequencing, and analyzing evolutionary relationships.Calcitonin: A peptide hormone that lowers calcium concentration in the blood. In humans, it is released by thyroid cells and acts to decrease the formation and absorptive activity of osteoclasts. Its role in regulating plasma calcium is much greater in children and in certain diseases than in normal adults.Antibodies, Protozoan: Immunoglobulins produced in a response to PROTOZOAN ANTIGENS.Receptors, IgG: Specific molecular sites on the surface of various cells, including B-lymphocytes and macrophages, that combine with IMMUNOGLOBULIN Gs. Three subclasses exist: Fc gamma RI (the CD64 antigen, a low affinity receptor), Fc gamma RII (the CD32 antigen, a high affinity receptor), and Fc gamma RIII (the CD16 antigen, a low affinity receptor).Hypergammaglobulinemia: An excess of GAMMA-GLOBULINS in the serum due to chronic infections or PARAPROTEINEMIAS.Dysgammaglobulinemia: An immunologic deficiency state characterized by selective deficiencies of one or more, but not all, classes of immunoglobulins.Antibody Affinity: A measure of the binding strength between antibody and a simple hapten or antigen determinant. It depends on the closeness of stereochemical fit between antibody combining sites and antigen determinants, on the size of the area of contact between them, and on the distribution of charged and hydrophobic groups. It includes the concept of "avidity," which refers to the strength of the antigen-antibody bond after formation of reversible complexes.Pregnancy: The status during which female mammals carry their developing young (EMBRYOS or FETUSES) in utero before birth, beginning from FERTILIZATION to BIRTH.Iodine Isotopes: Stable iodine atoms that have the same atomic number as the element iodine, but differ in atomic weight. I-127 is the only naturally occurring stable iodine isotope.Antibody Diversity: The phenomenon of immense variability characteristic of ANTIBODIES. It enables the IMMUNE SYSTEM to react specifically against the essentially unlimited kinds of ANTIGENS it encounters. Antibody diversity is accounted for by three main theories: (1) the Germ Line Theory, which holds that each antibody-producing cell has genes coding for all possible antibody specificities, but expresses only the one stimulated by antigen; (2) the Somatic Mutation Theory, which holds that antibody-producing cells contain only a few genes, which produce antibody diversity by mutation; and (3) the Gene Rearrangement Theory, which holds that antibody diversity is generated by the rearrangement of IMMUNOGLOBULIN VARIABLE REGION gene segments during the differentiation of the ANTIBODY-PRODUCING CELLS.Thyroid (USP): A dehydrated extract of thyroid glands from domesticated animals. After the removal of fat and connective tissue, the extract is dried or lyophilized to yield a yellowish to buff-colored amorphous powder containing 0.17-0.23% of iodine.UkraineImmunohistochemistry: Histochemical localization of immunoreactive substances using labeled antibodies as reagents.Cloning, Molecular: The insertion of recombinant DNA molecules from prokaryotic and/or eukaryotic sources into a replicating vehicle, such as a plasmid or virus vector, and the introduction of the resultant hybrid molecules into recipient cells without altering the viability of those cells.Antigens: Substances that are recognized by the immune system and induce an immune reaction.Sodium Iodide: A compound forming white, odorless deliquescent crystals and used as iodine supplement, expectorant or in its radioactive (I-131) form as an diagnostic aid, particularly for thyroid function tests.Transcription, Genetic: The biosynthesis of RNA carried out on a template of DNA. The biosynthesis of DNA from an RNA template is called REVERSE TRANSCRIPTION.Gene Expression Regulation: Any of the processes by which nuclear, cytoplasmic, or intercellular factors influence the differential control (induction or repression) of gene action at the level of transcription or translation.Immunoassay: A technique using antibodies for identifying or quantifying a substance. Usually the substance being studied serves as antigen both in antibody production and in measurement of antibody by the test substance.Lymphocyte Activation: Morphologic alteration of small B LYMPHOCYTES or T LYMPHOCYTES in culture into large blast-like cells able to synthesize DNA and RNA and to divide mitotically. It is induced by INTERLEUKINS; MITOGENS such as PHYTOHEMAGGLUTININS, and by specific ANTIGENS. It may also occur in vivo as in GRAFT REJECTION.Lymphoma: A general term for various neoplastic diseases of the lymphoid tissue.Immunoglobulin Km Allotypes: Allelic variants of the kappa light chains (IMMUNOGLOBULIN KAPPA-CHAINS) encoded by ALLELES of IMMUNOGLOBULIN LIGHT CHAIN GENES.Antibody-Producing Cells: Cells of the lymphoid series that can react with antigen to produce specific cell products called antibodies. Various cell subpopulations, often B-lymphocytes, can be defined, based on the different classes of immunoglobulins that they synthesize.Bence Jones Protein: An abnormal protein with unusual thermosolubility characteristics that is found in the urine of patients with MULTIPLE MYELOMA.Rheumatoid Factor: Antibodies found in adult RHEUMATOID ARTHRITIS patients that are directed against GAMMA-CHAIN IMMUNOGLOBULINS.Paraproteinemias: A group of related diseases characterized by an unbalanced or disproportionate proliferation of immunoglobulin-producing cells, usually from a single clone. These cells frequently secrete a structurally homogeneous immunoglobulin (M-component) and/or an abnormal immunoglobulin.Multiple Myeloma: A malignancy of mature PLASMA CELLS engaging in monoclonal immunoglobulin production. It is characterized by hyperglobulinemia, excess Bence-Jones proteins (free monoclonal IMMUNOGLOBULIN LIGHT CHAINS) in the urine, skeletal destruction, bone pain, and fractures. Other features include ANEMIA; HYPERCALCEMIA; and RENAL INSUFFICIENCY.Perchlorates: Compounds that contain the Cl(=O)(=O)(=O)O- structure. Included under this heading is perchloric acid and the salts and ester forms of perchlorate.Complement C3: A glycoprotein that is central in both the classical and the alternative pathway of COMPLEMENT ACTIVATION. C3 can be cleaved into COMPLEMENT C3A and COMPLEMENT C3B, spontaneously at low level or by C3 CONVERTASE at high level. The smaller fragment C3a is an ANAPHYLATOXIN and mediator of local inflammatory process. The larger fragment C3b binds with C3 convertase to form C5 convertase.Saliva: The clear, viscous fluid secreted by the SALIVARY GLANDS and mucous glands of the mouth. It contains MUCINS, water, organic salts, and ptylin.Republic of BelarusMice, Inbred C57BLSerologic Tests: Diagnostic procedures involving immunoglobulin reactions.Thyronines: A group of metabolites derived from THYROXINE and TRIIODOTHYRONINE via the peripheral enzymatic removal of iodines from the thyroxine nucleus. Thyronine is the thyroxine nucleus devoid of its four iodine atoms.Recombinant Proteins: Proteins prepared by recombinant DNA technology.Genes: A category of nucleic acid sequences that function as units of heredity and which code for the basic instructions for the development, reproduction, and maintenance of organisms.Protein Binding: The process in which substances, either endogenous or exogenous, bind to proteins, peptides, enzymes, protein precursors, or allied compounds. Specific protein-binding measures are often used as assays in diagnostic assessments.Paraproteins: Abnormal immunoglobulins synthesized by atypical cells of the MONONUCLEAR PHAGOCYTE SYSTEM. Paraproteins containing only light chains lead to Bence Jones paraproteinemia, while the presence of only atypical heavy chains leads to heavy chain disease. Most of the paraproteins show themselves as an M-component (monoclonal gammopathy) in electrophoresis. Diclonal and polyclonal paraproteins are much less frequently encountered.Transcription Factors: Endogenous substances, usually proteins, which are effective in the initiation, stimulation, or termination of the genetic transcription process.Neoplasms, Radiation-Induced: Tumors, cancer or other neoplasms produced by exposure to ionizing or non-ionizing radiation.Antigens, CD: Differentiation antigens residing on mammalian leukocytes. CD stands for cluster of differentiation, which refers to groups of monoclonal antibodies that show similar reactivity with certain subpopulations of antigens of a particular lineage or differentiation stage. The subpopulations of antigens are also known by the same CD designation.Myxedema: A condition characterized by a dry, waxy type of swelling (EDEMA) with abnormal deposits of MUCOPOLYSACCHARIDES in the SKIN and other tissues. It is caused by a deficiency of THYROID HORMONES. The skin becomes puffy around the eyes and on the cheeks. The face is dull and expressionless with thickened nose and lips.Methylthiouracil: A thiourea antithyroid agent that inhibits the synthesis of thyroid hormone. It is used in the treatment of hyperthyroidism.Antigens, Surface: Antigens on surfaces of cells, including infectious or foreign cells or viruses. They are usually protein-containing groups on cell membranes or walls and may be isolated.Reverse Transcriptase Polymerase Chain Reaction: A variation of the PCR technique in which cDNA is made from RNA via reverse transcription. The resultant cDNA is then amplified using standard PCR protocols.Cells, Cultured: Cells propagated in vitro in special media conducive to their growth. Cultured cells are used to study developmental, morphologic, metabolic, physiologic, and genetic processes, among others.Leukemia, Lymphoid: Leukemia associated with HYPERPLASIA of the lymphoid tissues and increased numbers of circulating malignant LYMPHOCYTES and lymphoblasts.Proto-Oncogene Proteins B-raf: A raf kinase subclass found at high levels in neuronal tissue. The B-raf Kinases are MAP kinase kinase kinases that have specificity for MAP KINASE KINASE 1 and MAP KINASE KINASE 2.Choristoma: A mass of histologically normal tissue present in an abnormal location.Thyrotropin, beta Subunit: The beta subunit of thyroid stimulating hormone, thyrotropin. It is a 112-amino acid glycopolypeptide of about 16 kD. Full biological activity of TSH requires the non-covalently bound heterodimers of an alpha and a beta subunit.Flow Cytometry: Technique using an instrument system for making, processing, and displaying one or more measurements on individual cells obtained from a cell suspension. Cells are usually stained with one or more fluorescent dyes specific to cell components of interest, e.g., DNA, and fluorescence of each cell is measured as it rapidly transverses the excitation beam (laser or mercury arc lamp). Fluorescence provides a quantitative measure of various biochemical and biophysical properties of the cell, as well as a basis for cell sorting. Other measurable optical parameters include light absorption and light scattering, the latter being applicable to the measurement of cell size, shape, density, granularity, and stain uptake.Potassium Iodide: An inorganic compound that is used as a source of iodine in thyrotoxic crisis and in the preparation of thyrotoxic patients for thyroidectomy. (From Dorland, 27th ed)Lingual Thyroid: A condition characterized by the presence of rudimentary THYROID tissue at the base of the TONGUE. It is due to failed embryonic development and migration of thyroid tissue to its normal location. The lingual thyroid usually cannot maintain adequate hormone production thereby resulting in HYPOTHYROIDISM.Waldenstrom Macroglobulinemia: A lymphoproliferative disorder characterized by pleomorphic B-LYMPHOCYTES including PLASMA CELLS, with increased levels of monoclonal serum IMMUNOGLOBULIN M. There is lymphoplasmacytic cells infiltration into bone marrow and often other tissues, also known as lymphoplasmacytic lymphoma. Clinical features include ANEMIA; HEMORRHAGES; and hyperviscosity.Complement Fixation Tests: Serologic tests based on inactivation of complement by the antigen-antibody complex (stage 1). Binding of free complement can be visualized by addition of a second antigen-antibody system such as red cells and appropriate red cell antibody (hemolysin) requiring complement for its completion (stage 2). Failure of the red cells to lyse indicates that a specific antigen-antibody reaction has taken place in stage 1. If red cells lyse, free complement is present indicating no antigen-antibody reaction occurred in stage 1.Transfection: The uptake of naked or purified DNA by CELLS, usually meaning the process as it occurs in eukaryotic cells. It is analogous to bacterial transformation (TRANSFORMATION, BACTERIAL) and both are routinely employed in GENE TRANSFER TECHNIQUES.Cell Differentiation: Progressive restriction of the developmental potential and increasing specialization of function that leads to the formation of specialized cells, tissues, and organs.Metamorphosis, Biological: Profound physical changes during maturation of living organisms from the immature forms to the adult forms, such as from TADPOLES to frogs; caterpillars to BUTTERFLIES.Electrophoresis, Polyacrylamide Gel: Electrophoresis in which a polyacrylamide gel is used as the diffusion medium.Receptors, IgE: Specific molecular sites on the surface of B- and T-lymphocytes which combine with IgEs. Two subclasses exist: low affinity receptors (Fc epsilon RII) and high affinity receptors (Fc epsilon RI).