DIFFERENTIAL DISTRIBUTION OF CALPAIN IN HUMAN LYMPHOID-CELLS

Calpain, a calcium-activated neutral proteinase, is ubiquitously prese nt in human tissues. To determine if lymphoid cells implicated in path ogenesis of demyelination may harbor calpain in a functionally active form, we determined both muCalpain and mCalpain activities in human ly mphoid cell lines. DEAE-cellulose and phenylsepharose column chromatog raphy were used to isolate the enzyme from the natural inhibitor, calp astatin. Lymphocytic lines (CCRF-CEM, MOLT-3, MOLT-4, M.R.) showed pre dominance of muCalpain (55-80%) whereas the monocytic line (U-937) sho wed predominance of mCalpain (77%). Proportion and subcellular distrib ution of both isoforms varied among cell lines. Calpains isolated from U-937 cells degraded myelin basic protein. These results indicate tha t human lymphoid cells harbor functionally active calpain that can deg rade myelin components in vitro. The study suggests a degradative role for calpain in demyelinating diseases.