A DNA-REPAIR ABNORMALITY SPECIFIC FOR REARRANGED IMMUNOGLOBULIN VARIABLE GENES IN GERMINAL CENTER B-CELLS

The somatic hypermutation mechanism produces high-rate mutagenesis spe cifically targeted to rearranged immunoglobulin (Ig) variable (V) gene segments during the germinal center (GC) stage of B lymphocyte differ entiation. The mechanism of this process remains uncertain, partly due to the lack of a direct assay for hypermutation activity. In this stu dy, a gene-specific DNA repair assay was used to compare the rate and quality of DNA repair in the mantle zone (MZ) and GC B cells at rearra nged and unrearranged Ig V genes. GC B cells were distinguished from M Z B cells by a retarded repair rate specific for rearranged Ig V genes . In addition, a unique feature of GC cells after DNA repair was the a ppearance of predominant mutations in rearranged Ig V(H)5 gene PCR pro ducts. These predominant mutations also occurred in natural mutants of V(H)5 genes. However, repair-associated mutations reflected, at least in part, ''template-jumping'' during amplification of the residually damaged genomic template. Overall, these findings reflect a repair abn ormality associated with the hypermutation process by the criteria of sequence- and B cell stage-specificity. We conclude that locus-specifi c retardation of DNA repair is a component of the hypermutation mechan ism. RFLP or SSCP analysis provides a simple assay to monitor this rep air abnormality as a surrogate biochemical marker for hypermutation du ring B cell differentiation. Copyright (C) 1996 Elsevier Science Ltd.