Altered memory B-cell homeostasis in human aging.

Previous studies of age-associated immune system changes revealed alterations in expressed immunoglobulin heavy chain variable domain repertoires, and variability in the fraction of expressed heavy chain variable domain genes with mutations. To test whether the latter finding reflected a variation in memory B-cell numbers, we measured circulating memory B cells of 11 healthy elderly subjects, 173 nursing-home residents, and 34 healthy young adults. A large fraction of old adults have low values for memory cells both as a percentage of all B cells and as an absolute memory B-cell concentration. The range of both values is much wider in old adults than in young adults, and it is much wider than the range of T-cell concentrations. Memory B-cell concentration, which was positively correlated with memory T-cell concentrations but inversely related to in vitro T-cell responses to mitogens, may reflect highly individual rates of immune senescence, and it may serve as an amplified marker of underlying T-cell function.