Age-dependent increase of memory B cell response to cytomegalovirus in healthy adults

Human cytomegalovirus (HCMV) may play an important role in immune system aging, due to its ability to modulate the host immune system. A significant age-related increase has been demonstrated for HCMV-specific serum antibody levels but so far, no information exists whether and to which extent the magnitude of the HCMV-specific memory B cell response develops with increasing age. We examined the size of the HCMV-specific memory B cell response and assessed whether there are quantitative differences in HCMV-specific memory B cell numbers and serum antibody titers against HCMV in young and older persons. The quantities of HCMV-specific memory B cells were determined in 20 young (20-31 years) and 21 older (60-80 years) healthy volunteers by limiting dilution analysis. HCMV-specific antibody levels were analyzed by ELISA. Our study demonstrates that higher HCMV-specific plasma antibody levels correlated well with the numbers of circulating HCMV-specific memory B cells and were not due to a generally higher antibody production in these individuals. The magnitude of HCMV-specific memory B cell responses was significantly higher in the group of older as compared to young subjects, but showed a high degree of individual variation in elderly persons. Together, the results of the present study indicate that the circulating memory B cell pool against HCMV increases during aging in humans. The expansion of HCMV-specific memory B cells and antibody titers possibly contribute to the sustained control of HCMV infection during old age.