Antibody multispecificity mediated by conformational diversity. (65/350)

A single antibody was shown to adopt different binding-site conformations and thereby bind unrelated antigens. Analysis by both x-ray crystallography and pre-steady-state kinetics revealed an equilibrium between different preexisting isomers, one of which possessed a promiscuous, low-affinity binding site for aromatic ligands, including the immunizing hapten. A subsequent induced-fit isomerization led to high-affinity complexes with a deep and narrow binding site. A protein antigen identified by repertoire selection made use of an unrelated antibody isomer with a wide, shallow binding site. Conformational diversity, whereby one sequence adopts multiple structures and multiple functions, can increase the effective size of the antibody repertoire but may also lead to autoimmunity and allergy.  (+info)

ATM is not required in somatic hypermutation of VH, but is involved in the introduction of mutations in the switch mu region. (66/350)

Class switch recombination (CSR) and somatic hypermutation (SHM) are mechanistically related processes that share common key factors such as activation-induced cytidine deaminase. We have previously shown a role for ATM (mutated in ataxia-telangiectasia) in CSR. In this paper we show that the frequency, distribution, and nature of base pair substitutions in the Ig variable (V) heavy chain genes in ataxia-telangiectasia patients are largely similar to those in normal donors, suggesting a normal SHM process. Characterization of the third complementarity-determining region in B cells from ataxia-telangiectasia patients also shows a normal V(D)J recombination process. SHM-like mutations could be identified in the switch (S) mu region (up to several hundred base pairs upstream of the S mu -S(alpha) breakpoints) in normal in vivo switched human B cells. In the absence of ATM, mutations can still be found in this region, but at less than half the frequency of that in normal donors. The latter mutations are mainly due to transitions (86% compared with 58% in controls) and are biased to A or T nucleotides. An ATM-dependent mechanism, different from that generating SHM in V genes, is therefore likely to be involved in introducing SHM-like mutations in the S region. ATM may thus be one of the factors that is not shared by the CSR and SHM processes.  (+info)

A new model of sheep Ig diversification: shifting the emphasis toward combinatorial mechanisms and away from hypermutation. (67/350)

The current model of Ig repertoire development in sheep focuses on the rearrangement of a small number (approximately 20) of Vlambda gene segments. It is believed that this limited combinatorial repertoire is then further diversified through postrearrangement somatic hypermutation. This process has been reported to introduce as many as 110 mutations/1000 nucleotides. In contrast, our data have that indicated somatic hypermutation may diversify the preimmune repertoire to a much lesser extent. We have identified 64 new Vlambda gene segments within the rearranged Ig repertoire. As a result, many of the unique nucleotide patterns thought to be the product of somatic hypermutation are actually hard-coded within the germline. We suggest that combinatorial rearrangement makes a much larger contribution, and somatic hypermutation makes a much smaller contribution to the generation of diversity within the sheep Ig repertoire than is currently acknowledged.  (+info)

Diversity of anti-HLA-DR antibodies elicited by distinct anti-idiotypic monoclonal antibodies recognizing idiotopes co-expressed by the immunizing monoclonal antibody. (68/350)

Analysis at the clonal level of the idiotypic network has identified differences in fine specificity between antigen-binding anti-anti-idiotypic (anti-anti-id) monoclonal antibody (mAb) and the original mAb as well as among antigen-binding anti-anti-idiotypic (anti-id) mAb. However, the diversity of humoral immune responses elicited by anti-id mAb recognizing idiotopes co-expressed on the immunizing mAb has not been analysed. Since this information may contribute to our understanding of the role of anti-id antibodies in the generation of diversity in the course of an immune response, we have compared the fine specificity and idiotype profile of two subsets of anti-HLA-DR mAb generated with the anti-id mAb F5-444 and F5-830. The latter mAb recognize idiotopes co-expressed in the antigen-combining site of the immunizing anti-HLA-DR1,4,w14,w8,9 mAb AC1.59. These investigations showed that: (1) the two subsets of anti-HLA-DR mAb overlap only partially in their reactivity patterns with HLA-DR+ cells; (2) both subsets of anti-HLA-DR mAb recognize spatially close epitopes; (3) each subset of anti-HLA-DR mAb has unique reactivity patterns with soluble HLA-DRw16 and DRw17 antigens; and (4) each subset of anti-anti-id mAb displays a distinct idiotype profile. The subtle differences in the fine specificity and idiotype profile of the two subsets of anti-HLA-DR mAb suggest that anti-id antibodies may play a role in the generation of diversity in the course of a humoral immune response.  (+info)

Antibody repertoire and gene expression profile: implications for different developmental and functional traits of splenic and peritoneal B-1 lymphocytes. (69/350)

In L2 mice, a high expression level of the transgenic lambda2(315) L chain results in nearly complete exclusion of endogenous L chains and a predominance of B-1a cells. In this study, we show that splenic and peritoneal B-1a cells differ considerably in their Ab repertoire and gene expression profile. Splenic B-1a cells exhibit a more diversified repertoire under L chain limitation. Despite oligoclonal overlaps between both B-1a compartments, some B cell receptor specificities are clearly restricted to the peritoneum. The capacity of peritoneal B-1a cells to enter the splenic B-1a compartment was found to be very limited. Gene expression profiling revealed genes up-regulated in splenic B-1a cells that are involved in mediating specialized first-line-of-defense effector functions and interaction with T cells. Thus, splenic and peritoneal B-1a cells differ not only in their developmental program but also in functional properties.  (+info)

Predominant autoantibody production by early human B cell precursors. (70/350)

During B lymphocyte development, antibodies are assembled by random gene segment reassortment to produce a vast number of specificities. A potential disadvantage of this process is that some of the antibodies produced are self-reactive. We determined the prevalence of self-reactive antibody formation and its regulation in human B cells. A majority (55 to 75%) of all antibodies expressed by early immature B cells displayed self-reactivity, including polyreactive and anti-nuclear specificities. Most of these autoantibodies were removed from the population at two discrete checkpoints during B cell development. Inefficient checkpoint regulation would lead to substantial increases in circulating autoantibodies.  (+info)

Memory B lymphocytes determine repertoire oligoclonality early after haematopoietic stem cell transplantation. (71/350)

The objective of this study was to investigate if oligoclonality of the Ig repertoire post-haematopoietic stem cell transplantation (HSCT) is restricted to memory B lymphocytes or if it is a general property among B lymphocytes. As a measure of B lymphocyte repertoire diversity, we have analysed size distribution of polymerase chain reaction (PCR) amplified Ig H complementarity determining region 3 (CDR3) in naive and memory B lymphocytes isolated from patients before HSCT and at 3, 6 and 12 months after HSCT as well as from healthy controls. We demonstrate a limited variation of the IgH CDR3 repertoire in the memory B lymphocyte population compared to the naive B cell population. This difference was significant at 3 and 6 months post-HSCT. Compared to healthy controls there is a significant restriction of the memory B lymphocyte repertoire at 3 months after HSCT, but not of the naive B lymphocyte repertoire. Twelve months after HSCT, the IgH CDR3 repertoire in both memory and naive B lymphocytes are as diverse as in healthy controls. Thus, our findings suggest a role for memory B cells in the restriction of the oligoclonal B cell repertoire observed early after HSCT, which may be of importance when considering reimmunization of transplanted patients.  (+info)

Heavy chain variable (VH) region diversity generated by VH gene replacement in the progeny of a single precursor cell transformed with a temperature-sensitive mutant of Abelson murine leukemia virus. (72/350)

Sequence analysis of a large number of DNA clones containing a functional heavy chain variable, diversity, and joining (VHDJH) complex generated by VH to VHDJH joining (VH gene replacement) in the progeny derived from a common precursor cell transformed with a temperature-sensitive (ts) Abelson murine leukemia virus (A-MuLV) indicates that endogenous VH gene replacement in vitro generates immunoglobulin gene joints distinct from those generated by the usual VH to DJH joining. Such joints keep the pentamer CAAGA at the 3' end of the donor VH segment and lack a recognizable D segment, as can be seen also in vivo. The results suggest that VH gene replacement participates in generating VH region diversity in vivo, as previously postulated. During the joining process, a unique VH gene was selected in all progeny cells, together with a single A nucleotide dominantly added to the junctional boundaries. The basis of these regulatory processes is discussed.  (+info)