Regulates cytotoxic granule exocytosis in effector lymphocytes, thus acting as a critical mediator of inflammation in a broad range of infectious and non-infectious diseases (PubMed:32839608). Essential for cytotoxic degranulation of natural killer (NK) cells and CD8(+) T-cells and for the activation of CD4(+) T-cells following infection (PubMed:32839608). Plays a critical role in CD8(+) T-cell and NK cell-mediated cytolysis of target cells and contributes to the cytolytic activity via the perforin/granzyme pathway by enhancing exocytosis of LAMP1-carrying lytic granules (PubMed:32839608, PubMed:33911019). Contributes to NK cell-mediated control of cancer metastasis (PubMed:32839608). Predominantly expressed by leukocytes with cytotoxic activity such as CD8(+) T-cells and natural killer cells. Up-regulated in CD4(+)T-cells in the liver and spleen upon infection with Leishmania donovani. Cytotoxic activity of natural killer cells and CD8(+) T-cells are defective in knockout mice (PubMed:32839608, PubMed:33911019). Mice fail to resolve Leishmania donovani infection, which is accompanied by a sustained reduction in the production of pro-inflammatory cytokines and a defective CD4(+) T-cell response (PubMed:32839608). Mice infected with Plasmodium berghei ANKA show a significant reduction in the recruitment of parasite-specific cytotoxic CD8(+) T cells to the brain, along with lower levels of inflammation (PubMed:32839608). Mice injected intravenously with B16F10 and LWT1 melanoma cell lines show a significant increase in the number of lung metastases compared with wild-type mice and an vitro impairment of natural killer cells to lyse susceptible tumor cells (PubMed:32839608). Belongs to the PMP-22/EMP/MP20 family.