CALPAIN SECRETED BY ACTIVATED HUMAN LYMPHOID-CELLS DEGRADES MYELIN

Calpain secreted by lymphoid (MOLT-3, M,R,) or monocytic (U-937, THP-1 ) cell lines activated with PMA and A23187 degraded myelin antigens, T he degradative effect of enzymes released in the extracellular medium was tested on purified myelin basic protein and rat central nervous sy stem myelin in vitro, The extent of protein degradation was determined by SDS-PAGE and densitometric analysis, Various proteinase inhibitors were used to determine to what extent protein degradation was mediate d by calpain and/or other enzymes, Lysosomal and serine proteinase inh ibitors inhibited 20-40 % of the myelin-degradative activity found in the incubation media of cell lines, whereas the calcium chelator (EGTA ), the calpain-specific inhibitor (calpastatin), and a monoclonal anti body to m calpain blocked myelin degradation by 60-80%, Since breakdow n products of MBP generated by calpain may include fragments with anti genic epitopes, this enzyme may play an important role in the initiati on of immune-mediated demyelination. (C) 1995 Wiley-Liss, Inc.