By contrast with Mtb-induced PD-1 expression on CD4 T cells, PD-1 expression was relatively low on CD8 T cells cultured for 6 days with CFP-10/ESAT-6 peptide pool and did not differ between individuals with LTBI and smear+ TB, with the majority of proliferating CFP-10/ESAT-6-specific CD8 T cells lacking PD-1 expression (data not shown). Here, PDCD1 is linked to tuberculosis.