Both CD45R(low) and CD45R(high) "revertant" CD4 memory T cells provide help for memory B cells

During a primary response to thymus dependent antigens, B cells undergo a n umber of qualitative changes to become memory B cells - processes that requ ire co-stimulatory signals and cytokine help from CD4 T cells. The question of whether distinct, antigen-experienced memory CD4 T cells are subsequent ly needed to program memory B cells into antibody synthesis has not been cl early resolved. Using an adoptive transfer model in which memory but not na ive B cells were stimulated, we evaluated CD4 T cell help using lymphocytes obtained from primed or unprimed thymectomized donors and expressing a nai ve (CD45R(high)) or a memory (CD45R(low)) phenotype. Memory B cells, most o f which were committed to the IgG1 (Th2) subclass, could be stimulated to p roduce antibody using help transferred by the CD45R(high) naive subset of u nprimed donors (slow onset of response), the CD45R(low) subset of 7 day pri med donors (large, rapid antibody response) or by both the CD45R(low) and t he CD45R(high) "revertant" subsets of 6 month primed donors. We found that antigen primed CD45R(low) CD4 T cells reverted (defaulted) with time to a C D45R(high) resting state, a change that was prevented by persisting antigen . The evidence suggests that CD4 memory T cells are partitioned into two di fferent functional states (CD45R(high) and CD45R(low)) and that these deter mine the characteristics of the memory B cell response in terms of speed, s ize and longevity.