The smear+ TB patients in our cohort were older than in our LTBI cohort (Table 1) and we found a weak positive correlation between age and PD-1 expression on total CD4 T cells (p = 0.04, r = 0.24; data not shown); however, we found no significant correlation between age and PD-1 expression on Mtb-specific CD4 or CD8 T cells (data not shown). Here, PDCD1 is linked to tuberculosis.