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 (By similarity). Essential for cytotoxic degranulation of natural killer (NK) cells and CD8(+) T-cells and for the activation of CD4(+) T-cells following infection (By similarity). 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 (By similarity). Contributes to NK cell-mediated control of cancer metastasis (By similarity). Expressed in activated T-cells, in kidney, liver, lung and pancreas. Not expressed in brain, heart, or skeletal muscle. Expressed at high levels in TCR gamma delta-expressing CTL clones, and in some TCR alpha beta-expressing CTL clones (both CD4+ and CD8+), but is not expressed in other TCR alpha beta-expressing CTL clones and in cell lines representing B-cells, monocytes, and myeloid cells. By CSF3/G-CSF (PubMed:7510105). Up-regulated in CD4(+) T-cells from peripheral blood mononuclear cells of patients with visceral leishmaniasis (PubMed:32839608). Belongs to the PMP-22/EMP/MP20 family.