CD27 and infection: The proportion of activated memory (CD27+,CD21-) B cells expressing CXCR3 and CD11c was significantly elevated in the TypP compared to the RP infant macaques (Fig 5E), and expression of these two markers on activated memory B cells directly correlated with the levels of anti-SIV antibodies present at week 10–12 post-infection (p<0.0001) (Fig 5F).