At day 32 post-infection, the numbers of B cells in the spleen of Il21-/- and Il21r-/- mice were reduced compared to WT C57BL/6 controls (S2 Fig), and this was reflected in the numbers of mature (M), transitional 1 (T1) and transitional 2 (T2) B cells (Fig 6, A-D). Here, IL21 is linked to infection.