MKI67 and infection: SVV infection induces the proliferation of B cells indicated by an increase in the frequency of Ki67 positive cells on days 7 to 14 compared to day 0 in marginal zone (MZ)-like (CD27+IgD+) and memory (CD27+IgD−) B cells, in BAL cells (Figure 4A) and PBMC (Figure 4B).