Dynamic interactions between CD4+ T cells and B cells are needed for humoral immunity and CD4+ T cell memory. It is not known whether B cells are needed early on to induce the formation of memory precursor cells or are needed later to sustain memory cells. Herein, primary and memory CD4+ T cells responses were followed in wildtype mice that were depleted of mature B cells by anti-CD20 before or different times after acute lymphocytic choriomeningitis virus (LCMV) infection. The antibody treatment led to a 1000-fold reduction in B cell number that lasted 6 weeks. Primary virus-specific CD4+ Th1 cells were generated in B cell-depleted mice, however, there was a decrease in the CD4+Ly6CloTbet+ memory precursor population and a corresponding 4-fold reduction in CD4+ memory cell number. Memory T cells showed impaired cytokine production when they formed without B cells. B cell-depletion had no effect on established memory populations. During disseminating virus infection, B cell depletion led to sustained weight loss, functional exhaustion of CD4+ and CD8+ T cells, and prevented mice from resolving the infection. Thus, B cells contribute to the establishment and survival of memory CD4+ T cells following acute infection and play an essential role in immune protection against disseminating virus infection
