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Genetic analysis of autoantibodies in idiopathic thrombocytopenic purpura reveals evidence of clonal expansion and somatic mutation. Blood 2002. [DOI: 10.1182/blood.v100.4.1388.h81602001388_1388_1398] [Citation(s) in RCA: 100] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Although idiopathic thrombocytopenic purpura (ITP) is the most common autoimmune hematologic disorder, little is known about the associated autoantibodies on a molecular level. Consequently, diagnostic assays and therapy for ITP lack specificity. To avoid technical limitations imposed by B-cell immortalization methods, we used repertoire cloning (Fab/phage display) to clone platelet autoantibodies and examine the relation between immunoglobulin (Ig) gene usage, clonality, and antigen specificity. Phage display libraries were constructed from splenocytes from 2 patients with chronic ITP, and competitive cell-surface selection was used to isolate several dozen unique IgG platelet-specific autoantibodies. Platelet-reactive Fabs in both patients were associated almost exclusively with rearrangements of a single Ig heavy-chain variable-region gene (VH3-30), despite an apparent diversity of antigen specificities. Comparative analysis of platelet-reactive Fab Ig gene rearrangements from each patient suggested that they evolved from a restricted number of B-cell clones through somatic mutation with high replacement-to-silent mutation ratios. Although VH3-30–encoded heavy chains were found with light chains encoded by several different Ig genes, molecular repairing experiments showed exquisite restriction on the specific heavy- and light-chain pairings that permitted platelet reactivity. Together, these data suggest that the development of platelet-reactive antibodies associated with ITP is driven by an encounter with diverse platelet antigens through the clonal expansion of B cells using genetically restricted and highly specific combinations of heavy- and light-chain gene products. The extraordinarily high usage of the VH3-30 heavy-chain gene in these patients has implications for the pathogenesis, diagnosis, and management of chronic ITP.
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Somatic Hypermutation, Clonal Diversity, and Preferential Expression of the VH 51p1/VL kv325 Immunoglobulin Gene Combination in Hepatitis C Virus–Associated Immunocytomas. Blood 1998. [DOI: 10.1182/blood.v91.7.2433] [Citation(s) in RCA: 194] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Abstract
A high prevalence of chronic hepatitis C virus (HCV) infection has recently been shown in a subset of B-cell non-Hodgkin's lymphomas, most of which belong to the lymphoplasmacytoid lymphoma/immunocytoma subtype and are characterized by the production of a monoclonal IgM cryoglobulin with rheumatoid factor activity. To better define the stage of differentiation of the malignant B cell and to investigate the role of chronic antigen stimulation in the pathogenesis of the HCV-associated immunocytomas, we analyzed the variable (V) region gene repertoire in 16 cases with this type of tumor. The lymphoma-derived V gene sequences were successfully determined in 8 cases; 5 of them expressed the 51p1 VH gene in combination with the kv325 VL gene. Moreover, a monoclonal 51p1-expressing B-cell population was detected in 4 of the remaining immunocytomas by an allele-specific Ig gene fingerprinting assay, indicating that HCV-associated immunocytomas represent clonal proliferations of a highly selected B-cell population. Somatic mutations and intraclonal diversity were observed in all of the lymphoma V genes, and clonally related IgM and IgG VH transcripts indicative of isotype switching were present in one case. These findings are consistent with an antigen-driven process and support a role for chronic antigen stimulation in the growth and clonal evolution of HCV-associated immunocytomas.
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Somatic Hypermutation, Clonal Diversity, and Preferential Expression of the VH 51p1/VL kv325 Immunoglobulin Gene Combination in Hepatitis C Virus–Associated Immunocytomas. Blood 1998. [DOI: 10.1182/blood.v91.7.2433.2433_2433_2442] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
A high prevalence of chronic hepatitis C virus (HCV) infection has recently been shown in a subset of B-cell non-Hodgkin's lymphomas, most of which belong to the lymphoplasmacytoid lymphoma/immunocytoma subtype and are characterized by the production of a monoclonal IgM cryoglobulin with rheumatoid factor activity. To better define the stage of differentiation of the malignant B cell and to investigate the role of chronic antigen stimulation in the pathogenesis of the HCV-associated immunocytomas, we analyzed the variable (V) region gene repertoire in 16 cases with this type of tumor. The lymphoma-derived V gene sequences were successfully determined in 8 cases; 5 of them expressed the 51p1 VH gene in combination with the kv325 VL gene. Moreover, a monoclonal 51p1-expressing B-cell population was detected in 4 of the remaining immunocytomas by an allele-specific Ig gene fingerprinting assay, indicating that HCV-associated immunocytomas represent clonal proliferations of a highly selected B-cell population. Somatic mutations and intraclonal diversity were observed in all of the lymphoma V genes, and clonally related IgM and IgG VH transcripts indicative of isotype switching were present in one case. These findings are consistent with an antigen-driven process and support a role for chronic antigen stimulation in the growth and clonal evolution of HCV-associated immunocytomas.
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