Identification of CD19(-)B220(+)c-Kit(+)Flt3/Flk-2(+)cells as early B lymphoid precursors before pre-B-I cells in juvenile mouse bone marrow. (57/1345)

The combined analysis of the expression of receptor tyrosine kinases c-Kit and Flt3/Flk-2 and of the human CD25 gene expressed as a transgene under the regulation of the mouse lambda5 promoter in the bone marrow of 1-week-old mice allows us to identify three stages of B lymphocyte development before the CD19(+)c-Kit(+) pre-B-I cells. Single-cell PCR analysis of the rearrangement status of the Ig heavy chain alleles allows us to order these early stages of B cell development as follows: (i) B220(+)CD19(-)c-Kit(lo)Flt3/Flk-2(hi)lambda5(-), (ii) B220(+)CD19(-)c-Kit(lo)Flt3/Flk-2(hi)lambda5(+) and (iii) B220(+)CD19(+)c-Kit(lo)Flt3/Flk-2(lo)lambda5(+) before B220(+)CD19(+)c-Kit(lo)Flt3/Flk-2(-)lambda5(+) pre-B-I cells. All these progenitors are clonable on stromal cells in the presence of IL-7 and can differentiate to CD19(+)c-Kit(-) B-lineage cells. A combination of stem cell factor, Flt3 ligand and IL-7 was also able to support the proliferation and differentiation of the progenitors in a suspension culture. Furthermore, the analyses indicate that the onset of D(H)J(H) rearrangements precedes the expression of the lambda5 gene. These progenitor populations were characteristic of juvenile mice and could not be detected in the bone marrow of adult mice. Hence the expression pattern, and probably the function, of the receptor tyrosine kinases in early B cell differentiation appears to be different in juvenile and adult mice.  (+info)

Loss of N-glycolylneuraminic acid in human evolution. Implications for sialic acid recognition by siglecs. (58/1345)

The common sialic acids of mammalian cells are N-acetylneuraminic acid (Neu5Ac) and N-glycolylneuraminic acid (Neu5Gc). Humans are an exception, because of a mutation in CMP-sialic acid hydroxylase, which occurred after our common ancestor with great apes. We asked if the resulting loss of Neu5Gc and increase in Neu5Ac in humans alters the biology of the siglecs, which are Ig superfamily members that recognize sialic acids. Human siglec-1 (sialoadhesin) strongly prefers Neu5Ac over Neu5Gc. Thus, humans have a higher density of siglec-1 ligands than great apes. Siglec-1-positive macrophages in humans are found primarily in the perifollicular zone, whereas in chimpanzees they also occur in the marginal zone and surrounding the periarteriolar lymphocyte sheaths. Although only a subset of chimpanzee macrophages express siglec-1, most human macrophages are positive. A known evolutionary difference is the strong preference of mouse siglec-2 (CD22) for Neu5Gc, contrasting with human siglec-2, which binds Neu5Ac equally well. To ask when the preference for Neu5Gc was adjusted in the human lineage, we cloned the first three extracellular domains of siglec-2 from all of the great apes and examined their preference. In fact, siglec-2 had evolved a higher degree of recognition flexibility before Neu5Gc was lost in humans. Human siglec-3 (CD33) and siglec-6 (obesity-binding protein 1) also recognize both Neu5Ac and Neu5Gc, and siglec-5 may have some preference for Neu5Gc. Others showed that siglec-4a (myelin-associated glycoprotein) prefers Neu5Ac over Neu5Gc. Thus, the human loss of Neu5Gc may alter biological processes involving siglec-1, and possibly, siglec-4a or -5.  (+info)

CD22 forms a quaternary complex with SHIP, Grb2, and Shc. A pathway for regulation of B lymphocyte antigen receptor-induced calcium flux. (59/1345)

CD22 is a cell surface molecule that regulates signal transduction in B lymphocytes. Tyrosine-phosphorylated CD22 recruits numerous cytoplasmic effector molecules including SHP-1, a potent phosphotyrosine phosphatase that down-regulates B cell antigen receptor (BCR)- and CD19-generated signals. Paradoxically, B cells from CD22-deficient mice generate augmented intracellular calcium responses following BCR ligation, yet proliferation is decreased. To understand further the mechanisms through which CD22 regulates BCR-dependent calcium flux and proliferation, interactions between CD22 and effector molecules involved in these processes were assessed. The adapter proteins Grb2 and Shc were found to interact with distinct and specific regions of the CD22 cytoplasmic domain. Src homology-2 domain-containing inositol polyphosphate-5'-phosphatase (SHIP) also bound phosphorylated CD22, but binding required an intact CD22 cytoplasmic domain. All three molecules were bound to CD22 when isolated from BCR-stimulated splenic B cells, indicating the formation of a CD22.Grb2.Shc.SHIP quaternary complex. Therefore, SHIP associating with CD22 may be important for SHIP recruitment to the cell surface where it negatively regulates calcium influx. Although augmented calcium responses in CD22-deficient mice should facilitate enhanced c-Jun N-terminal kinase (JNK) activation, BCR ligation did not induce JNK activation in CD22-deficient B cells. These data demonstrate that CD22 functions as a molecular "scaffold" that specifically coordinates the docking of multiple effector molecules, in addition to SHP-1, in a context necessary for BCR-dependent SHIP activity and JNK stimulation.  (+info)

Modulation of the major histocompatibility complex class II-associated peptide repertoire by human histocompatibility leukocyte antigen (HLA)-DO. (60/1345)

Antigen presentation by major histocompatibility complex class II molecules is essential for antibody production and T cell activation. For most class II alleles, peptide binding depends on the catalytic action of human histocompatibility leukocyte antigens (HLA)-DM. HLA-DO is selectively expressed in B cells and impedes the activity of DM, yet its physiological role remains unclear. Cell surface iodination assays and mass spectrometry of major histocompatibility complex class II-eluted peptides show that DO affects the antigenic peptide repertoire of class II. DO generates both quantitative and qualitative differences, and inhibits presentation of large-sized peptides. DO function was investigated under various pH conditions in in vitro peptide exchange assays and in antigen presentation assays using DO(-) and DO(+) transfectant cell lines as antigen-presenting cells, in which effective acidification of the endocytic pathway was prevented with bafilomycin A(1), an inhibitor of vacuolar ATPases. DO effectively inhibits antigen presentation of peptides that are loaded onto class II in endosomal compartments that are not very acidic. Thus, DO appears to be a unique, cell type-specific modulator mastering the class II-mediated immune response induced by B cells. DO may serve to increase the threshold for nonspecific B cell activation, restricting class II-peptide binding to late endosomal compartments, thereby affecting the peptide repertoire.  (+info)

Role for cathepsin F in invariant chain processing and major histocompatibility complex class II peptide loading by macrophages. (61/1345)

The major histocompatibility complex (MHC) class II-associated invariant chain (Ii) regulates intracellular trafficking and peptide loading of MHC class II molecules. Such loading occurs after endosomal degradation of the invariant chain to a approximately 3-kD peptide termed CLIP (class II-associated invariant chain peptide). Cathepsins L and S have both been implicated in degradation of Ii to CLIP in thymus and peripheral lymphoid organs, respectively. However, macrophages from mice deficient in both cathepsins S and L can process Ii and load peptides onto MHC class II dimers normally. Both processes are blocked by a cysteine protease inhibitor, indicating the involvement of an additional Ii-processing enzyme(s). Comparison of cysteine proteases expressed by macrophages with those found in splenocytes and dendritic cells revealed two enzymes expressed exclusively in macrophages, cathepsins Z and F. Recombinant cathepsin Z did not generate CLIP from Ii-MHC class II complexes, whereas cathepsin F was as efficient as cathepsin S in CLIP generation. Inhibition of cathepsin F activity and MHC class II peptide loading by macrophages exhibited similar specificity and activity profiles. These experiments show that cathepsin F, in a subset of antigen presenting cells (APCs), can efficiently degrade Ii. Different APCs can thus use distinct proteases to mediate MHC class II maturation and peptide loading.  (+info)

CD19 and CD22 regulate a B lymphocyte signal transduction pathway that contributes to autoimmunity. (62/1345)

The fate of B lymphocytes is dependent on intrinsic and B cell antigen receptor (BCR)-induced signals. These signals are modified and interpreted by other cell-surface molecules such as CD19 and CD22 that govern mature B cell activation. This review assesses our current understanding of how CD19 and CD22 regulate B lymphocyte signaling and how alterations in these response-regulators contribute to autoimmunity in mice and humans. We propose that CD19 functions as a specialized adapter protein that regulates B lymphocyte signaling and autoantibody production. Overexpression of CD19 by B cells in systemic sclerosis patients correlates with autoantibody production and transgenic mice that overexpress CD19 produce similar autoantibodies. CD19 establishes a novel Src-family kinase activation loop that regulates basal signal transduction thresholds in resting B cells and amplifies Src-family kinase activation following BCR ligation. Reciprocally, CD22 is a potent regulator of CD19 function. These observations provide insight into how CD19 and CD22 govern the molecular ordering and intensity of signals transduced in B cells that may contribute to autoimmunity.  (+info)

A phase I study of combination therapy with immunotoxins IgG-HD37-deglycosylated ricin A chain (dgA) and IgG-RFB4-dgA (Combotox) in patients with refractory CD19(+), CD22(+) B cell lymphoma. (63/1345)

This study used an 8-day continuous infusion regimen of a 1:1 mixture of two immunotoxins (ITs) prepared from deglycosylated ricin A chain (dgA) conjugated to monoclonal antibodies directed against CD22 (RFB4-dgA) and CD19 (HD37-dgA; Combotox) in a Phase I trial involving 22 patients with refractory B cell lymphoma to determine the maximum tolerated dose, clinical pharmacology, and toxicity profile and to characterize any clinical responses. Adult patients received a continuous infusion of Combotox at 10, 20, or 30 mg/m2/192 h. No intrapatient dose escalation was permitted. Patients with > or =50 circulating tumor cells (CTCs)/mm3 in peripheral blood tolerated all doses without major toxicity. The maximum level of serum IT (Cmax) achieved in this group was 345 ng/ml of RFB4-dgA and 660 ng/ml of HD37-dgA (1005 ng/ml of Combotox). In contrast, patients without CTCs (<50/mm3) had unpredictable clinical courses that included two deaths probably related to the IT. Additionally, patients exhibited a significant potential for association between mortality and a history of either autologous bone marrow or peripheral blood stem cell transplants (P2 = 0.003) and between mortality and a history of radiation therapy (P2 = 0.036). In patients with CTCs, prior therapies appeared to have little impact on toxicity. Subsequent evaluation of the ITs revealed biochemical heterogeneity between two lots of HD37-dgA. In addition, HD37-dgA thawed at the study site tended to contain significant particulates, which were not apparent in matched controls stored at the originating site. This suggests that a tendency to aggregate may have resulted from shipping, storage, and handling of the IT that occurred prior to preparation for administration. It is not clear to what extent, if any, the aggregation of HD37-dgA IT was related to the encountered clinical toxicities; however, the potential to aggregate does suggest one possible basis for problems in our clinical experience with HD37-dgA and leads us to the conclusion that non-aggregate-forming formulations for these ITs should be pursued prior to future clinical trials.  (+info)

Sequential treatment of a resistant chronic lymphocytic leukemia patient with bryostatin 1 followed by 2-chlorodeoxyadenosine: case report. (64/1345)

Bryostatin 1 (Bryo-1) has been shown to differentiate chronic lymphocytic leukemia (CLL) cells to the hairy cell leukemia phenotype. The purine analogue 2-chlorodeoxyadenosine (2-CdA) exhibits enhanced activity in patients with hairy cell leukemia compared to those with CLL. Here we present a case report of a patient diagnosed with resistant CLL and treated sequentially with Bryo-1 followed by 2-CdA for three cycles. Molecular and biochemical parameters relative to the sequential treatment with these agents in vivo were comparable to those found in the WSU-CLL cell line in vitro (R. M. Mohammad et al., Clin. Cancer Res., 4: 445-453, 1998; R. M. Mohammad et al., Biol. Chem., 379: 1253-1261, 1998). There was a significant reduction of lymphocyte count from 37.1 x 10(3)/microl before the treatment to 3.4 x 10(3)/microl after treatment, and partial remission was achieved 2 months after the treatment. The percentage of morphologically differentiated lymphocytes was increased from 3% before treatment to 92% with the first cycle of Bryo-1. Similarly, expression of CD22, a marker of differentiation, increased from 38% to 97% and was maintained at a high level for the duration of the treatment. Analysis of the molecular markers of apoptosis in isolated peripheral blood lymphocytes revealed an increase in the Bax:Bcl-2 ratio after treatment with Bryo-1 in cycles 2 and 3, with associated poly(ADP-ribose) polymerase cleavage after Bryo-1 and 2-CdA treatment. The deoxycytidine kinase: cytosolic 5'-nucleotidase activity ratio increased modestly after Bryo-1 treatment, indicating increased sensitivity of the peripheral blood lymphocytes to 2-CdA. In summary, we found that sequential treatment with Bryo-1 and 2-CdA caused a significant reduction in peripheral blood lymphocytes (CLL cells) with simultaneous induction of differentiation and the initiation of the Bax: Bcl-2 apoptotic pathway.  (+info)