Age-related decrease in the proportion of germinal center B cells from mouse Peyer's patches is accompanied by an accumulation of somatic mutations in their immunoglobulin genes.

Somatic hypermutation of immunoglobulin genes and the generation of memory B cells seems to take place in germinal centers, which are chronically present in Peyer's patches. Age-associated changes in the germinal center B cell compartment of Peyer's patches and in the mutations of a kappa light chain transgene were analyzed in unimmunized mice. Somatic mutations accumulate in germinal center B cells slowly and continuously to reach an apparent plateau when the animals are around 5 months old. In contrast, the proportion of germinal center B cells reaches a maximum in very young mice (about 2 months old) and decreases progressively thereafter. These results suggest that the highly mutated B cells in older mice arise by the successive accumulation of mutations in memory cells. The data also show that the optimum time for the analysis of hypermutation of transgenes in Peyer's patches is when the mice are about 5 months old.