To investigate mechanisms involved in establishing both central and effector memory, we analysed Ag-specific TM cells soon after they had formed, 7 days after infection with Lm-2W1S, and separated 2W1S-specific CD4 T cells into CXCR5-ve Tem and CXCR5+ve Tcm cells (Figure 6A). This evidence concerns the gene CD4 and infection.