CXCR3 and infection: First, the duration and intensity of antigen receptor signaling depends on the: (1) nature and duration of infection; (2) expression of chemokine receptors (CXCR3 and CCR5) that regulate T cell/antigen-presenting cell (APC) interactions and the anatomical localization of the responding cells (Hu et al., 2011; Kohlmeier et al., 2011; Kurachi et al., 2011); (3) the stage of infection at which naïve T cells are recruited to the response (early responders versus latecomer cells; Badovinac et al., 2004; D’Souza and Hedrick, 2006).