CD4 and listeriosis: Using the IL-2-GFP reporter mice, both in vitro and in the ActA-deficient Listeria monocytogenes infection model in vivo, a recent study reported that within 24 hours, newly activated CD4+ T cells already split into two populations: IL-2+ cells enriched for Bcl6 mRNA expression and IL-2– T cells expressing higher mRNA levels of Prdm1, S1pr1, and Klf258.