Although initial observations of expanded CD21lo B cell numbers were primarily in the context of chronic immune activation, more recent studies in both mice and humans have shown that CD21lo T-bet+ or CD11c+ B cells expand rapidly after infection or immunization (36, 41, 45, 55), after which they slowly decline over several months (36, 38, 41, 56) (Figure 1). Here, ITGAX is linked to infection.