LYMPHOPAIN, A CYTOTOXIC T-CELL-ASSOCIATED AND NATURAL-KILLER CELL-ASSOCIATED CYSTEINE PROTEINASE

Through differential screening of established human leukaemia cell lin es, we have identified and molecularly cloned lymphopain, a novel cyst eine proteinase of the papain family. Lymphopain exhibits a remarkably restricted cellular pattern of expression, being predominantly expres sed in cytotoxic T-lymphocytes and natural killer cells. The human lym phopain locus maps to chromosome 11q13, encodes a polypeptide of 376 a mino acids and is conserved in the mouse. Both human and murine forms appear more closely related to protozoan papain like enzymes than to o ther mammalian members of the papain family. The cellular distribution of lymphopain expression, together with the functional demonstration of lymphopain-associated proteinase activity in vitro, is suggestive o f a role for lymphopain in immune cell-mediated, cell killing.