PDCD1 and infection: A previous study showed that a variety of bacterial-derived TLR ligands could induce PD-1 expression on human macrophages, suggesting that TLR signaling pathways played an important role in regulating PD-1.23 Although no ‘exhausted'-like phenotype has been observed in PD-1+ macrophages, the induced anti-inflammatory cytokine profile in PD-1+ macrophages has ramifications for the proper functioning of the immune system during infection.24