Age-related alterations of somatic hypermutation and CDR3 lengths in humanV kappa 4-expressing B lymphocytes

The lower avidity and/or affinity of antibodies generated by an aged immune system could be attributed to two major changes in the antibody repertoire : a shift in germline gene usage and a decrease in the rate of immunoglobul in hypermutation. In an attempt to identify the mechanisms involved in the observed humoral immune deficiency in the elderly, we studied whether diffe rences in the somatic diversity of a particular VK region occurred with age ing. By using the polymerase chain reaction and sequencing, we analysed and compared V kappa 4-J kappa rearrangements isolated from young (mean age 21 years) and aged (mean age 83 years) healthy adults. Mutations in the V kap pa 4 gene compared with the germline sequence were determined as well as th e length and structure of the CDR3 sequence. We analysed in detail various mechanisms contributing to CDR3 and VK variability in rearrangements involv ing the V kappa 4 gene. Our data revealed that, despite strong individual v ariations, significantly lower levels of somatic mutation were found in the aged group, both for complementarity-determining regions (CDRs) and framew ork regions (FRs) encoding V kappa 4 sequences. This decrease mostly affect ed mutations responsible for replacements and thus resulted in a lowered so matic diversification of the encoded V kappa 4 proteins in aged individuals . Moreover, comparison of the CDR3 regions of the V kappa 4-C kappa cDNA re vealed changes in light-chain junctional diversity that correlated with age . Altogether these data suggest an impaired light-chain somatic diversity i n connection with human senescence.