Memory B cells form in aged mice despite impaired affinity maturation and germinal center kinetics.

We examined whether age alters the emergence of high-affinity germinal center B (GCB) cells and switched memory B cells (swBmem) during a primary immune response to a thymus-dependent antigen, using a novel flow cytometric assay to distinguish relative BCR affinity. In young mice, high-affinity B cells predominate in the GCB pool and comprise a smaller proportion of the nascent swBmem pool two weeks after immunization. In aged mice, we observe significant reductions of high-affinity clones among GCB cells, but not nascent swBmem cells. The defect in GC affinity maturation was not overcome by providing excess carrier-specific T cells from young mice, as these cells still displayed compromised effector TFH differentiation in the aged animals. Our results suggest that B cells in aged animals have a reduced ability to prompt effector TFH differentiation, leading to a compromised GC response that results in reduced generation of high-affinity GCB and plasma cells; despite normal production of early swBmem cells.