AUTOANTIBODIES AGAINST HEAT-SHOCK-PROTEIN-60 MEDIATE ENDOTHELIAL CYTOTOXICITY

Stress or heat shock proteins (hsp) are a family of approximately two dozen proteins with a high degree of amino acid sequence homology betw een different species, ranging from prokaryotes to humans, and are rep resentative of a generalized response to environmental and metabolic s tressors, Our previous studies showed increased expression of human hs p60 on endothelial cells of arterial intima with atherosclerotic lesio ns, and elevated levels of serum antibodies (Ab) against hsp65/60 in s ubjects with carotid atherosclerosis, To investigate the possible invo lvement of anti-hsp65/60 Ab in endothelial injury, specific hsp-Ab wer e isolated from human high titer sera by affinity chromatography and p robed on heat-shocked human umbilical vein endothelial cells, Purified human anti-hsp65/60 Ab reacted specifically with mycobacterial hsp65, human hsp60, and a 60-kD protein band of heat-shocked endothelial cel ls, High levels of hsp60 mRNA expression in endothelial cells were fou nd between 4 and 12 h after 30 min treatment at 42 degrees C, In immun ofluorescence tests, positive staining of heat-stressed endothelial ce lls was observed not only in the cytoplasm but also on the cell surfac e, Furthermore, only heat-stressed, but not untreated, Cr-51-labeled e ndothelial cells were lysed by antih-sp65/60 Ab in the presence of com plement (complement-mediated cytotoxicity) or peripheral blood mononuc lear cells (antibody-dependent cellular cytotoxicity), Control Abs, in cluding human anti-hsp65/60 low titer antiserum, human Ig fraction dep rived of hsp65/60 Ab, and mAbs to Factor VIII, alpha-actin, hsp70, and CD3 showed no cytotoxic effect, In conclusion, human serum anti-hsp65 antibodies act as autoantibodies reacting with hsp60 on stressed endo thelial cells and are able to mediate endothelial cytotoxicity, Thus, a humoral immune reaction to hsp60 may play an important role in the p athogenesis of atherosclerosis.