• Langerhans cells are dendritic cells found in the skin and function by internalizing antigens (foreign particles) and presenting them to T cells. (wikipedia.org)
  • Langerhans cell histiocytosis (LCH) is a group of idiopathic disorders characterized by the presence of cells with characteristics similar to bone marrow-derived Langerhans cells juxtaposed against a backdrop of hematopoietic cells, including T-cells, macrophages, and eosinophils. (medscape.com)
  • In 1868, Paul Langerhans discovered the epidermal dendritic cells that now bear his name. (medscape.com)
  • The ultrastructural hallmark of the Langerhans cell, the Birbeck granule, was described a century later. (medscape.com)
  • The term Langerhans cell histiocytosis is generally preferred to the older term, histiocytosis X. This newer name emphasizes the histogenesis of the condition by specifying the type of lesional cell and removes the connotation of the unknown ("X") because its cellular basis has now been clarified. (medscape.com)
  • Although the epidermal Langerhans cell has been presumed to be the cell of origin in LCH, recent studies have called this belief into question. (medscape.com)
  • Specifically, a variety of other cellular populations have been identified that possess phenotypic characteristics similar to Langerhans cells, including expression of CD207 and Birbeck granules. (medscape.com)
  • Therefore, in addition to epidermal Langerhans cells, other potential cellular origins for LCH include dermal langerin + dendritic cells, lymphoid tissue-resident langerin + dendritic cells, and monocytes that can be induced by local environmental stimuli to acquire a Langerhans cell phenotype. (medscape.com)
  • Notably, LCH cells have been found to express markers of both resting epidermal Langerhans cells (CD1a, intracellular major histocompatibility complex II [MHCII], Birbeck granules) and activated Langerhans cells (including CD54 and CD58). (medscape.com)
  • As a result, the pathologic cells of LCH have been hypothesized to represent Langerhans cells in a state of arrested maturation. (medscape.com)
  • [ 3 ] Taken together, these findings have led some to speculate that LCH is not a specific disease of epidermal Langerhans cells, but rather one of mononuclear phagocyte dysregulation. (medscape.com)
  • More recently, histiocytic diseases have been reclassified into five groups: (1) Langerhans-related, (2) cutaneous and mucocutaneous, (3) malignant histiocytosis, (4) Rosai-Dorfman disease, and (5) hemophagocytic lymphohistiocytosis and macrophage activation syndrome. (medscape.com)
  • The pathogenesis of Langerhans cell histiocytosis (LCH) is unknown. (medscape.com)
  • Broadly speaking, they can be divided into Langerhans and non-Langerhans cell histiocytoses. (thedoctorsdoctor.com)
  • Langerhans cell histiocytoses are all defined by the presence of a unique ultrastructural organelle, the Birbeck granule. (thedoctorsdoctor.com)
  • Currently, the preferred term is Langerhans cell histiocytosis. (thedoctorsdoctor.com)
  • Langerhans cell histiocytosis presenting in the neonatal period: a retrospective case series. (thedoctorsdoctor.com)
  • OBJECTIVES: To describe the morphologic characteristics of skin lesions, extent of extracutaneous disease, and outcomes in patients with neonatal presentation of Langerhans cell histiocytosis (LCH), and to examine clinical predictors of disease prognosis. (thedoctorsdoctor.com)
  • Epidemiologic study of Langerhans cell histiocytosis in children. (thedoctorsdoctor.com)
  • OBJECTIVE: The etiology and pathogenesis of Langerhans cell histiocytosis (LCH) remain poorly understood. (thedoctorsdoctor.com)
  • Langerhans cell histiocytosis is a rare disease involving clonal proliferation of langerhans cells seen in children and young adults. (scirp.org)
  • We report a rare case of adult Langerhans cell histiocytosis in the dorsal spine causing a spinal cord compression associated with a pulmonary process treated by surgery, radiotherapy and systemic therapy with good evolution. (scirp.org)
  • They all share histologically a significant infiltration of affected tissues by langerhans cells. (scirp.org)
  • Final diagnosis was therefore Langerhans cell histiocytosis of the dorsal spine complicated by spinal cord compression. (scirp.org)
  • A chest CT scan revealed a tumoral process measuring 25 mm at the lower lobe of the left lung evoking a Langerhans cell histiocytosis ( Figure 3 ). (scirp.org)
  • It consists of Langerhans cells with oval, grooved and convoluted nucleus and slightly eosinophilic cytoplasm, associated with eosinophils, lymphocytes and plasma cells (H & E × 400). (scirp.org)
  • Langerhans cell histiocytosis (LCH) is a proliferation of dendritic mononuclear cells with infiltration into organs locally or diffusely. (msdmanuals.com)
  • Гістіоцитоз легеневих клітин Лангерганса Pulmonary Langerhans cell histiocytosis (PLCH) is proliferation of monoclonal Langerhans cells in lung interstitium and airspaces. (msdmanuals.com)
  • Langerhans cell histiocytosis (LCH) is a dendritic cell (antigen-presenting cell) disorder. (msdmanuals.com)
  • Symptoms and signs of Langerhans cell histiocytosis vary considerably depending on which organs are infiltrated. (msdmanuals.com)
  • Genotyping of 69 histiocytic lesions revealed that 23/48 Langerhans cell lesions were BRAF -V600E-mutant whereas all non-Langerhans cell lesions (including dendritic cell sarcoma, juvenile xanthogranuloma, Rosai-Dorfman disease, and granular cell tumor) were wild-type. (oncotarget.com)
  • In conclusion, BRAF mutations in histiocytic proliferations are restricted to lesions of the Langerhans-cell type. (oncotarget.com)
  • Langerhans cell histiocytosis (LCH) is a disease characterized by the abnormal proliferation of leukocytes in the liver, lung and spleen. (histio.org)
  • Single-system Pulmonary Langerhans cell histiocytosis (PLCH) is an uncommon type of Langerhans cell histiocytosis that affects only the lung. (histio.org)
  • Langerhans cell histiocytosis (LCH) is blood disease which is now recognized as a cancer and can affect virtually any organ system of the body. (histio.org)
  • It is believed that cigarette smoke attracts specific immune cells in the lungs (Langerhans cells) which leads to a cascade of inflammation and injury to the air passages and lung tissue over time. (histio.org)
  • The exact prevalence of single-system Pulmonary Langerhans cell histiocytosis (PLCH) is unknown. (histio.org)
  • Necrobiotic xanthogranuloma is a rare, chronic and progressive, non-Langerhans cell histiocytosis disease typically characterized by multiple, indurated, asymptomatic to pruritic, yellow-orange plaques or nodules that tend to ulcerate and are usually located in the periorbital area, trunk and/or extremities. (nih.gov)
  • Idiopathic non-malignant disease characterized by idiopathic infiltration and accumulation of abnormal histiocytes (i.e. the Langerhans cells) within various tissues (bone marrow, skin, central nervous system, lung, liver, spleen, lymph nodes) causing focal or systemic effects. (capsulehealth.one)
  • At this point, Birbeck granules were thought to be exclusive to epidermal Langerhans cells, skin-restricted cells of the mononuclear phagocyte system. (capsulehealth.one)
  • Histiocytosis X was renamed Langerhans-cell histiocytosis , reflecting the concept that LCH cells represented dysfunctional epidermal Langerhans cells. (capsulehealth.one)
  • Over the next decades, reviews debated whether LCH was a disorder of transformed Langerhans cells or of normal Langerhans cells rendered pathologic by inappropriate stimuli. (capsulehealth.one)
  • Available at: http://www.cancernetwork.com/oncology-journal/langerhans-cell-histiocytosis-emerging-insights-and-clinical-implications [Accessed 1 Jul. (capsulehealth.one)
  • Langerhans cells are named after Paul Langerhans , a bright, young medical student who worked with the new technique of gold colloid staining in the mid-19th century. (capsulehealth.one)
  • In 1868 , Langerhans described an epidermal cell population, accounting for approximately 1% of epidermal cells, with characteristic dendrites that he described as extracutaneous nerves. (capsulehealth.one)
  • We now know that epidermal Langerhans cells are not nerves but dendritic cells, a heterogeneous group of hematopoietic cells enriched in interface tissues and lymphoid organs. (capsulehealth.one)
  • Epidermal Langerhans cells are unique among dendritic cells in that they arise not from myeloid progenitor cells in bone marrow but rather from yolk-sac progenitors and fetal liver-derived monocytes that populate the skin before birth and are maintained locally under steady-state conditions. (capsulehealth.one)
  • Langerhans cells are dendritic antigen-presenting cells. (capsulehealth.one)
  • A 2010 study comparing gene expression of cells expressing CD207 (a marker of Langerhans cells) in LCH lesions with epidermal CD207+ control cells identified differential expression of more than 2000 genes between these 2 subsets. (medscape.com)
  • Symptoms of Langerhans' Cell Histiocytosis vary depending on the part of the body affected and the severity of the disease. (homeremedylifestyle.com)
  • Langerhans' cell histiocytosis can cause symptoms in the skin, bones, lungs, and other parts of the body. (homeremedylifestyle.com)
  • The symptoms of Langerhans' cell histiocytosis include pain, swelling, and brown or red skin sores. (homeremedylifestyle.com)
  • Langerhans' cell histiocytosis is a rare disease . (homeremedylifestyle.com)
  • Children with Langerhans' cell histiocytosis have a high risk of developing cancer. (homeremedylifestyle.com)
  • Single-system Langerhans' cell histiocytosis responds well to chemotherapy. (homeremedylifestyle.com)
  • Multisystem Langerhans' cell histiocytosis, however, is fatal in severe cases. (homeremedylifestyle.com)
  • The treatment for Langerhans' cell histiocytosis will depend on the organs affected. (homeremedylifestyle.com)
  • Having a diagnosis of Langerhans' Cell Histiocytosis can be a scary time for a family. (homeremedylifestyle.com)
  • A diagnosis of Langerhans' Cell Histiocytosis is dependent on a number of factors. (homeremedylifestyle.com)
  • A diagnosis of Langerhans' cell histiocytosis should be made only after the patient has undergone a biopsy . (homeremedylifestyle.com)
  • The antibody is a new monoclonal antibody against a C-type lectin found on the surface of Langerhans cells. (homeremedylifestyle.com)
  • Another way to diagnose Langerhans cell histiocytosis is by examining the lymph nodes. (homeremedylifestyle.com)
  • The best way to treat Langerhans' cell histiocytosis is to have the disease treated by experts who understand the disease. (homeremedylifestyle.com)
  • Approximately one out of every 200,000 children develops Langerhans cell histiocytosis every year. (homeremedylifestyle.com)
  • Langerhans cell histiocytosis (LCH) is a rare haematological neoplasm characterized by the accumulation of CD1a + , CD207/Langerin + histiocytes within inflammatory lesions. (biomedcentral.com)
  • In the 1970s , Steinman and Cohn distinguished dendritic cells from macrophages on the basis of specific morphologic features of dendritic cells and their superior capacity to present antigens to and activate antigen-specific T cells. (capsulehealth.one)
  • Histiocytosis is a group of rare diseases characterized by inflammation and accumulation of cells derived from monocytes and macrophages in different tissues. (bvsalud.org)
  • LCH lesion also contains inflammatory cells and cytokines such as T lymphocytes, eosinophils, neutrophils, and macrophages. (capsulehealth.one)
  • CD11c is expressed in monocytes, macrophages, natural killer cells, some granulocytes and less so in a subset of lymphocytes. (thermofisher.com)
  • Host recognition of microbes happens through pattern reputation receptors, including Toll-like receptors (TLRs)2 that are indicated on many cells, including macrophages, monocytes (1), and keratinocytes (2). (cancer-ecosystem.com)
  • Data from our lab showed that expression of the mutated form of Braf in cells of the monocytes induced LCH-like disease in mice (these animals are called FRBRAF mice). (histio.org)
  • We concluded that monocytes expressing the mutated form of Braf are the cell of origin of systemic LCH in mice. (histio.org)
  • Methods We stimulated purified monocytes and whole peripheral blood mononuclear cells (PBMCs) from patients with GPA, patients with MPA or healthy controls with PR3 or MPO and visualised MGC and granuloma-like structure formation using light, confocal and electron microscopy, as well as measuring the cell cytokine production. (bmj.com)
  • and all cases showed typical morphology of Kikuchi disease, with necrosis, karyorrhectic debris, and the presence of the typical cell types, namely crescentic histiocytes and plasmacytoid monocytes. (medscape.com)
  • Malignant histiocytosis is a rare hereditary disease found in the Bernese Mountain Dog and humans, characterized by histiocytic infiltration of the lungs and lymph nodes. (wikipedia.org)
  • better source needed] Other breeds with a possible genetic tendency toward malignant histiocytosis include Rottweilers, Flat-Coated Retrievers, and Golden Retrievers. (wikipedia.org)
  • Genetics of Malignant Histiocytosis in the Bernese Mountain Dog. (wikipedia.org)
  • The working group of the Histiocyte Society divided histocytic disorders into three groups: (1) dendritic cell histiocytosis, (2) macrophage-related disorders, and (3) malignant histiocytosis. (medscape.com)
  • Histiocytosis and Neoplasms of Macrophage-Dendritic Cell Lineages: Multimodality Imaging with Emphasis on PET/CT. (nih.gov)
  • Since patients with GPA have augmented neutrophil PR3 expression, and PR3-expressing apoptotic cells frustrate macrophage phagocytosis and cellular clearance, we investigated the role of PR3 in stimulating giant cell and granuloma formation. (bmj.com)
  • Malignant lymphoma composed of large B lymphoid cells whose nuclear size can exceed normal macrophage nuclei, or more than twice the size of a normal lymphocyte. (lookformedical.com)
  • Development of Epstein-Barr virus-associated lymphoproliferative disorder and hemophagocytic lymphohistiocytosis during long-term lenalidomide maintenance therapy in multiple myeloma. (u-tokyo-hemat.com)
  • The abnormal cells in LCH have abnormal proliferation and lower antigen-presenting capability. (capsulehealth.one)
  • 10] Interestingly, this analysis found no differences in expression of proliferation markers between these subsets of CD207+ cells, consistent with the hypothesis that LCH may be a disease of abnormal cellular accumulation. (medscape.com)
  • Histiocytic disorders refer to diseases that are caused by abnormal behavior of these cells. (wikipedia.org)
  • Arguments supporting the reactive nature of LCH include the occurrence of spontaneous remissions, the extensive elaboration of multiple cytokines by dendritic cells and T-cells (the so-called cytokine storm) in LCH lesions, and the good survival rate in patients without organ dysfunction. (medscape.com)
  • The clinical manifestations of the currently recognized disease entities are highly variable and range from benign localized lesions to highly aggressive systemic diseases[ 4 ]. (oncotarget.com)
  • Two decades later, with the advent of electron microscopy, Nezelof and colleagues identified a unique intracellular organelle, the Birbeck granule , in histiocytosis X lesions. (capsulehealth.one)
  • The biopsy specimen from the right maxillary sinus showed soft tissue infiltration with myeloid leukemic cells, consistent with a chloroma. (contemporarypediatrics.com)
  • These differences were found in genes involved in cell cycle regulation, apoptosis, cell signaling, metastasis, and myeloid differentiation. (medscape.com)
  • CCDC88C-FLT3 gene fusion in CD34-positive haematopoietic stem and multilineage cells in myeloid/lymphoid neoplasm with eosinophilia. (u-tokyo-hemat.com)
  • These neoplastic cells are the result of sporadic activating mutations in genes of the mitogen-activated protein kinase (MAPK) signaling pathway expressed by multipotent hematopoietic stem/progenitor cells or committed myeloid precursors [ 1 ]. (biomedcentral.com)
  • Using a more sensitive technique for detection of mutant BRAF alleles (droplet digital PCR) [ 9 ], BRAF V600E was not detected in DNA extracted from myeloid or lymphoid cells isolated by flowcytometric sorting from a peripheral blood sample collected at the time of the fourth bone sample. (biomedcentral.com)
  • RUNX1 mutations have been reported in approximately 10% of myelodysplastic cases, 5-15% of acute myeloid leukemia, 8-37% of chronic myelomonocytic leukemia, 10% of T cell acute lymphoblastic leukemia, 3% of systemic mastocytosis, 2% of essential thrombocythemia and 2% of polycythemia vera. (cornell.edu)
  • RUNX1 mutations are independently associated with unfavorable outcomes and shorter survival after hematopoietic stem cell transplantation in patients with myelodysplastic syndrome and myelodysplastic syndrome/acute myeloid leukemia. (cornell.edu)
  • Any of a group of malignant tumors of lymphoid tissue that differ from HODGKIN DISEASE, being more heterogeneous with respect to malignant cell lineage, clinical course, prognosis, and therapy. (lookformedical.com)
  • RUNX1 mutations are also associated with an unfavorable prognosis chronic myelomonocytic leukemia and systemic mastocytosis. (cornell.edu)
  • On the other hand, the infiltration of organs by a monoclonal population of aberrant cells, the possibility of lethal evolution, and the cancer-based modalities of successful treatment are all consistent with a neoplastic process. (medscape.com)
  • Letterer-Siwe disease was described in infants with aggressive and generally fatal systemic disease, including skin, liver, spleen, and bone marrow infiltration by reticuloendothelial cells. (capsulehealth.one)
  • Genotyping identified a 45 year-old woman with an aggressive and treatment-refractory, ultrastructurally confirmed systemic BRAF -mutant LCH. (oncotarget.com)
  • Approximately 60% of the patients with LCH carry a mutation in a gene (BRAF) that controls cell growth. (histio.org)
  • It was recently shown that a mutated form of Braf, an oncogene that is involved in directing cell growth, is present in 60% of the patients with LCH. (histio.org)
  • We found that transplant of bone marrow cells from a BRAF mouse into a normal recipient animal promoted development of a LCH-like disease in the liver, spleen and lung but not in the brain. (histio.org)
  • To identify a treatment-responsive BRAF V600E mutation in brainstem neurohistiocytosis, where no lesional tissue was readily obtainable, using a cell-free DNA approach. (neurology.org)
  • Cell-free DNA was extracted from urine and allele-specific PCR for the BRAF V600E mutation was performed. (neurology.org)
  • Response to conventional treatment (corticosteroids and interferon) and targeted treatment with a BRAF inhibitor was assessed by clinical evaluation, gadolinium-enhanced MRI brain scan, and serial testing of urinary cell-free DNA for mutant alleles. (neurology.org)
  • Analysis of urinary cell-free DNA using allele-specific PCR for BRAF V600E mutations allows rapid noninvasive identification of a highly treatment-responsive pathway, leading to clinical and radiologic remission of disease. (neurology.org)
  • The diagnosis of histiocytosis is based on the clinic, radiological findings and pathological anatomy. (bvsalud.org)
  • Lichtenstein proposed a common diagnosis, histiocytosis X , with the X indicating an uncertain cell of origin. (capsulehealth.one)
  • 1949: Black-Schaffer advanced the diagnosis, proved the systemic nature of this disease, and raised the suspicion of an infectious cause for Whipple disease. (medscape.com)
  • A surgical biopsy showed an infiltrate of eosinophilic cells with oval, grooved and convoluted nucleus, associated with eosinophils, lymphocytes and plasma cells ( Figure 2 ). (scirp.org)
  • In immunohistochemical study, these eosinophilic cells expressed CD1a and S100 protein. (scirp.org)
  • CD11c is expressed by dendritic cells, a subset of Intestinal Intraepithelial Lymphocytes (IEL) and some activated T cells. (thermofisher.com)
  • A group of heterogeneous lymphoid tumors generally expressing one or more B-cell antigens or representing malignant transformations of B-lymphocytes. (lookformedical.com)
  • They are short-lived cells resembling bursa-derived lymphocytes of birds in their production of immunoglobulin upon appropriate stimulation. (lookformedical.com)
  • A form of non-Hodgkin lymphoma having a usually diffuse pattern with both small and medium lymphocytes and small cleaved cells. (lookformedical.com)
  • A classification of B-lymphocytes based on structurally or functionally different populations of cells. (lookformedical.com)
  • Lymphadenitis results from apoptotic cell death induced by cytotoxic T lymphocytes. (medscape.com)
  • The most common clinical manifestation of Kikuchi disease is cervical lymphadenopathy, with or without systemic signs and symptoms. (medscape.com)
  • Sinus histiocytosis with massive lymphadenopathy (SHML), initially described in 1969 by Rosai and Dorfman,[ 22 ] is a rare, nonneoplastic lymphoproliferative disorder that is characterized by its histological features. (surgicalneurologyint.com)
  • Identification of genomic alterations that drive the clinically aggressive serous and clear cell tumors of the endometrium. (researchgate.net)
  • The term "oncotarget" encompasses all molecules, pathways, cellular functions, cell types, and even tissues that can be viewed as targets relevant to cancer as well as other diseases. (oncotarget.com)
  • Chromosomes are the cellular storage units for genes contained within the nucleus (which is the genetic center) of the cell and are analogous to a spool with the DNA or genetic message being the thread on the spool. (sarcomahelp.org)
  • Note: In this classification, the following terms are used to define and to represent other terms that are referable to these categories 042-044. (cdc.gov)
  • Lymphoma b cell. (lookformedical.com)
  • B-cell antigens are expressed on the immature cells that make up the tumor in virtually all cases of Burkitt lymphoma. (lookformedical.com)
  • Discordant lymphomas of classic Hodgkin lymphoma and peripheral T-cell lymphoma following dupilumab treatment for atopic dermatitis. (u-tokyo-hemat.com)
  • The only common feature among these tumors is the absence of giant REED-STERNBERG CELLS, a characteristic of Hodgkin's disease. (lookformedical.com)
  • B-cell lymphoid tumors that occur in association with AIDS. (lookformedical.com)
  • While the origin of these tumors is still not definitively known, the two theories with the most support suggest that these tumors arise from a primitive cell derived either from an embryologic tissue called the neural crest, or from resident cells in the body (called mesenchymal stem cells) that have a capability to become one of a variety of tissue types. (sarcomahelp.org)
  • Tumors in the Ewing's family of sarcomas are made of primitive cells, which are cells that haven't yet decided what type of cell they are. (sarcomahelp.org)
  • They can be functional, exhibiting a hormonal hypersecretion syndrome, but can be non-functional presenting with non-specific symptoms and include insulinoma, glucagonoma, VIPoma, somatostatinoma (SSoma), PPoma and Zollinger-Ellison syndrome (ZES, or gastrinoma) and other ectopic hormone producing tumors (such as GRFoma) (see these terms). (findzebra.com)
  • Pancreatic neuroendocrine tumors (also called islet cell tumors) - NETs that typically arise in the pancreas, although they can occur outside the pancreas. (findzebra.com)
  • In this proposal we will define which cell is important for development of disease in the mouse model and how it causes disease. (histio.org)
  • In the most severe form of the disease, the cancer cells can spread to other parts of the body. (homeremedylifestyle.com)
  • The resulting stem cells are known as hematopoietic or blood-forming stem cells because they are similar to bone marrow cells, which have been widely used in the treatment of a variety of genetic disorders, blood diseases, and autoimmune diseases such as lupus, diabetes , and kidney disease , as well as in post-cancer therapies. (stemcellcareindia.com)
  • Today, Umbilical Cord Blood (UCB) stem cells are used in the treatment of over 105 ailments in Thailand, including cardiovascular disease, cancer, hereditary/genetic diseases, and blood disorders such as sickle cell anaemia. (stemcellcareindia.com)
  • Click on the number after each disease term to retrieve COVID-19 related articles. (cdc.gov)
  • To obtain more information about each disease, click the link on the disease term that leads to the Rare Disease PHGKB . (cdc.gov)
  • Monoclonal antibodies, such as blinatumomab, may induce changes in the body's immune system and may interfere with the ability of cancer cells to grow and spread. (policylab.us)
  • Giving monoclonal antibody therapy with chemotherapy may kill more cancer cells. (policylab.us)
  • Histopathology of peripheral nerve and sympathetic ganglion from a patient with autonomic failure, oat-cell carcinoma of the lung, and positive anti-HU antibody titer. (medscape.com)
  • The marrow specimen showed extensive replacement of normal hematopoietic elements by immature monocytic cells. (contemporarypediatrics.com)
  • A general term for various neoplastic diseases of the lymphoid tissue. (lookformedical.com)
  • Cord blood contains unusually high quantities of adult stem cells, which eventually grow into hematopoietic blood cells. (stemcellcareindia.com)
  • Stem cells are nature's pharmacy and can be found in everyone's bone marrow, adipose fat, tooth pulp derived or peripheral blood. (stemcellcareindia.com)
  • A histiocyte is a differentiated tissue cell that has its origin in the bone marrow. (wikipedia.org)
  • Donors of blood, on the other hand, will have to go through multiple tests for clearance before receiving a series of GSF injections to encourage the release of cells from the bone marrow into the blood. (stemcellcareindia.com)
  • Independent origins of fetal liver haematopoietic stem and progenitor cells. (u-tokyo-hemat.com)