Multi‐parametric flow cytometry can be used to define the populations of T cells responding to infection within a CHIM, identifying CD4+ and CD8+ T‐cell phenotypes: naïve versus memory subsets; activation markers (e.g., CD38, HLA‐DR and CD137); CD4+ T follicular helper cells (CXCR5, PD‐1); exhaustion/senescence (CD57, KLRG1, PD‐1, TIM‐3); cytotoxic activity (GrxB, CD107a); polyfunctional T cells (Th1/Th2 cytokine profiles); and proliferation. The gene discussed is CD4; the disease is infection.