CD4 and infection: Flow cytometry analysis revealed that, although conventional CD4+ T cells gradually express CXCR5, PD-1, Bcl6, and SLAM and produce high levels of IL-21 after infection, TCRβ+CD1d-tetramer+ NKT cells do not upregulate Bcl6, CXCR5, or PD-1 and express moderate levels of SLAM and IL-21 (Figures 2A and 2B; Figures S2A–S2D).