Granzyme B is a serine protease most commonly found in the granules of cytotoxic lymphocytes (CTLs) and natural killer cells (NK cells). It is secreted by these cells along with the pore forming protein perforin to mediate apoptosis in target cells. Granzyme B has also more recently found to be produced by a wide range of non-cytotoxic cells ranging from basophils and mast cells to smooth muscle cells. Granzyme B has shown to be involved in inducing inflammation by stimulating cytokine release and is also involved in extracellular matrix remodelling. Elevated levels of granzyme B are also implicated in a number of autoimmune diseases, several skin diseases, and type 1 diabetes.