Seven major T and natural killer (NK) cell clusters were identified (Fig. 3 a and Fig. S1 j), including a population resembling naïve, circulating CD4+ T cells (T cell CD4 Ccr7; Fig. S1 n) that decreased in frequency as infection progressed in both mouse strains, albeit earlier in C57BL/6 mice (Fig. 3 d; and Fig. S1, j and k). The gene discussed is CCR7; the disease is infection.