PDCD1 (Programmed cell death 1), also called PD1, encodes a cell surface receptor that is a member of the B7 superfamily involved in immunomodulation. This gene is mapped to 2q37.3. PDCD1 acts as an inhibitory molecule on T cells after interacting with its ligands PDL1 and PDL2. The PDCD1 gene contains 5 exons. This protein is expressed in pro-B-cells and is thought to play a role in their differentiation. Using flow cytometric analysis, It has been found that expression of PDCD1 was upregulated on CD16-positive and CD16-negative monocytes, but not on dendritic cells, in viremic HIV-positive patients, but not in highly active antiretroviral therapy (HAART)-treated HIV-positive patients. PDCD1 upregulation in monocytes was induced by microbial Toll-like receptor ligands and inflammatory cytokines.