Molecular Analysis of Human Immunoglobulin Heavy Chain Variable Genes (IgVH) in Normal and Malignant B Cells

Abstract

Antigen binding to the membrane-bound immunoglobulin (Ig) receptor is crucial for clonal survival during B cell development and antigenic stimulation of mature B cells. 41 Together with co-stimulatory signals (eg, CD40 and cytokines) it controls B cell proliferation and differentiation. 37 In the past, molecular analysis of Ig genes has been used mostly to prove clonality of a malignant lymphoproliferation. A detailed analysis, however, reveals that much more can be learned because clonal development, selection processes by antigen, and Ig variable gene (IgV) hypermutation leave a fingerprint of individual clonal development and current activities.The quality of antigen binding is determined primarily by recombination events during ontogeny involving VH, D, and JH genes and, later in the development, VL and JL genes as well as subsequent somatic hypermutation of IgVH and IgVL genes during antigenic responses of mature B cells. 49 Signaling by the Ig receptor eventually rescues pre-B cells and proliferating mature B cells from apoptotic cell death. It thereby forms the basis of a lifelong recurring selection process that is reflected by the Ig receptor repertoire and molecular composition of the Ig receptors in B lymphocyte populations of individuals at different ages. The molecular recombination of VH, D, and JH genes in developing B lymphocytes is probably a random process that would lead to a random use of functional VH genes as determined by their frequency in seven different VH gene families. 9 However, positive or negative selection due to differences in antibody binding efficiency or antigen availability lead to relative over-or underrepresentation of distinctive VH families and VH genes in the receptor repertoire of fetal B lymphocytes. Subsequent antigenic exposure to environmental, infectious, or self antigens on an individual and genetic basis further influences clonal sizes of mature B cell families by usage and selection of distinct VH genes, thereby affecting their frequencies in the adult B cell population. The mechanism of somatic hypermutation of IgV genes is still not completely understood. Functionally, it represents the molecular basis of affinity maturation of naive B cell populations after antigenic exposure and interactions. On a molecular basis it consists of a site-specific hypermutability linked to the transcription of IgV genes acting from the 5Ј of the IgV gene promotor to around 1.5 kb downstream. The constant region exon, which is separated from the variable region by several kilobases of intron, is not affected. Mutations consisting mainly of point mutations accumulate within the antigen-binding complementary determining regions (CDR) in a nonrandom pattern. Rarely, duplications and deletions are also found. 15,57 The somatic hypermutation process is dependent on B cell differentiation and maturation. Pregerminal center B cells usually exhibit unmutated germline receptors. Antigen-activated proliferating germinal center B cells show high mutation rates and evidence of ongoing mutati...

A spindle cell variant of diffuse large B-cell lymphoma possesses genotypic and phenotypic markers characteristic of a germinal center B-cell origin

“…Immunoglobulin gene mutations accumulate during B-cell transit through the germinal center and are maintained after B-cell exit from the germinal center. 11,13 Recent evidence indicates that normal germinal center B cells also acquire mutations within the noncoding regions of the BCL-6 proto-oncogene. [14][15][16] Phenotypic B-cell markers include BCL-6 and CD10 proteins, which are expressed after germinal center entry, and MUM1 and CD138/syndecan-1 proteins, which are expressed during the late stages of B-cell maturation.…”

“…Well-defined histogenetic markers of B-cell lymphoma currently include mutations of immunoglobulin and BCL-6 genes and expression of CD10, BCL-6, MUM1, and CD138/syndecan-1 antigens. [11][12][13][14][15][16][17][18][19] These markers are useful indicators of the origin and differentiation stage of B-cell lymphoma because each are retained upon neoplastic transformation.…”

Analysis of the immunoglobulin heavy chain gene variable region of CD5-positive and -negative diffuse large B cell lymphoma

“…Ongoing mutation (intraclonal microheterogeneity) is linked to the germinal center (GC) microenvironment in normal immune reaction. 5 It is reported that FL has an intraclonal microheterogeneity resulting from the ongoing mutation which occurs in the neoplastic lesion, because FL tends to display a similar architecture to the normal reactive follicle. [26][27][28] However, it remains unclear whether B cell lymphomas with a diffuse architecture show intraclonal microheterogeneity.…”

“…[1][2][3][4][5][6] The degree of somatic mutation found in VH genes from normal B cells depends on their level of differentiation during the immune response. Somatic mutation rates in various B cell neoplasms often correspond to those of their normal cellular counterparts.…”

“…Somatic mutation rates in various B cell neoplasms often correspond to those of their normal cellular counterparts. 5,6 For example, the rearranged VH genes of B cell neoplasms derived from pregerminal center (GC) B cells such as mantle cell lymphoma (MCL) exhibit sequences with little or no somatic mutation. Those of B cell neoplasms derived from GC B cells and post GC B cells, such as follicular lymphoma (FL), diffuse large B cell lymphoma (DLBCL) and multiple myeloma, are somatically mutated.…”