Perforin

Identifies a cytolytic protein stored in the granules of cytotoxic T lymphocytes (CTLs), which enables these cells to destroy targets presenting foreign antigens. Perforin is highly expressed in CD8⁺ T cells and, to a lesser degree, in γ/δ T cells and NK cells. It can be useful for detecting activated CTLs in conditions such as severe graft-versus-host disease, chronic renal rejection, peripheral T-cell lymphomas, and in identifying NK-cell lymphomas.