SELL and infection: This was paralleled by an increase in the percentage of CD4 T cells with an effector memory phenotype (CD62L− CD45RA−, P<0.05), while the frequencies of terminal effector (CD62L− CD45RA+) and central memory (CD62L+ CD45RA−) CD4 T cells remained roughly constant throughout infection (Fig. 3D–E, upper panel).