A protein found in the cytoplasmic granules of both T cytotoxic lymphocytes and natural killer cells. This protein is implicated in target cell lysis by the above cells. [L. per-foro, to bore, pierce, + -in]
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per·for·in (purґfə-rin) a protein expressed by cytotoxic lymphocytes and forming a transmembrane pore at the site of target cell lysis.Medical dictionary. 2011.