CD40LG and infection: IgG+(CD95+) MBC and IgM+CD95+CD21− MBC (clusters 10, 11, and 14) are enriched for Spike specificity, but these populations are also observed in the B cell compartments of the TT, Flu, and RSV antigens encountered longer ago (Figure 3B), consistent with the formation of a long-lived memory response after infection.