Significance of endogenous heat shock protein in adjuvant arthritis

Objective. To investigate the role of endogenous heat shock protein (HSP) (rat 60 kDa HSP, rHSP 60) in adjuvant arthritis (AA), the expression of rHSP 60 in AA-susceptible Lewis rats and AA-resistant Fisher rats was studied. Methods. The extent of arthritis was assessed by measuring footpad thickness. The proliferative response of mononuclear cells (MNC) to mycobacterial 65 kDa HSP (mHSP 65) was measured by [³H] thymidine incorporation. The messenger RNA for rHSP 60 was quantified by dot blot hybridization in peripheral blood mononuclear cells (PBMNC), splenic MNC (SMNC), and ankle joint synovial membrane (SM). Results: In Lewis rats: AA developed on Day 14 after immunization with Freund's complete adjuvant. Proliferative responses of PBMNC and SMNC to mHSP 65 were observed on Day 14 and thereafter according to the development of AA. Messenger RNA levels of rHSP 60 in PBMNC, SMNC, and SM did not increase until Day 21. In Fisher rats: AA and proliferative response of MNC to mHSP 65 were not observed throughout the observation period. Messenger RNA levels of rHSP 60 were significantly higher in preimmune Fisher rats than those in preimmune Lewis rats. Messenger RNA levels of rHSP 60 in PBMNC and SMNC increased significantly on Day 7 and decreased to preimmune levels until Day 21. Conclusion. We propose that elevated levels and rapid elevation of endogenous HSP 60 levels relate to resistance to AA in Fisher rats; however, lower levels and delayed increase of endogenous HSP 60 levels relate to susceptibility to AA in Lewis rats.