Programmed cell death protein 1 was present on higher proportion of CD4highCD8low DP T cells than CD4lowCD8high DP T cells both in chronic (median 46.7% vs 19.3%; P < 0.0001) and past (median 44.2% vs 28.6%; P = 0.003) infection (Figure 4A). Here, PDCD1 is linked to infection.