Evidence for heat shock protein immunity in a rat cardiac allograft model of chronic rejection

Background The stress response to injury concept has been proposed as a mec hanism of chronic rejection. This hypothesis has been tested with a rat car diac allograft model in recipients pretreated with donor bone marrow (BM) c ells. Chronic rejection is manifested in this BM group by obliterative arte riopathy and the epicardium and endocardium contains lymphocytic infiltrate s resembling Quilty lesions. Pretreatment with a liver allograft (the ortho topic liver transplant [OLTx] group) is associated with an absence of chron ic rejection in the transplanted heart. Methods and Results. Stress responses in the allograft were assessed by det ermining heat shock protein (hsp) expression by immunohistology of graft ti ssues and immunoblot analysis of stromal tissue lysates with monoclonal ant ibodies (mAb) to mammalian hsp60, the inducible hsp72, the constitutively e xpressed hsc73, and the grp78 C-terminal sequence KSEKDEL (grp78seq), Immun ostaining showed clusters of grp78seq-positive cells in the inflammatory in filtrates of obliterated blood vessels and Quilty lesions in the BM group o f cardiac allografts. Such grp78seq-positive cells were not seen in the OLT x group of heart allografts nor in syngrafts, Neither group showed signific antly different graft myocyte staining of grp78 or hsp72, whereas hsp60 and hsc73 showed higher expression in the BM group and, Do a lesser extent, th e OLTx group. The increased expression of hsc73 was seen especially in the obliterated arteries and in myocytes nearby cellular infiltrates. Immunoblo t analysis of graft stromal tissue lysates showed additional bands with mAb to hsp60 and hsc73 for the OLTx and especially the BM group. No significan t bands were seen for hsp72 and grp78. Lymphocytes isolated from chronically rejecting allografts reacted with irr adiated autologous spleen cells in the presence of mycobacterial hsp65 and interleukin-2, Culturing of graft-infiltrating cells with mycobacterial hsp 71 and interleukin-a yielded lymphocyte clones without alloreactivity, but with strong proliferative responsiveness to self-antigen-presenting cells a nd, only in the presence of mycobacterial hsp71 or murine grp78, This T-cel l reactivity seemed to require intact hsp molecules because treatment of hs p71 with proteolytic enzymes, polymyxin, or ATP abrogated this induction of the stimulatory effect of self-antigen-presenting cells. These T cells are similar to the hsp-dependent, autoreactive lymphocytes cloned from acutely rejecting rat allografts, Conclusions. These findings support the concept that the pathogenesis of ch ronic rejection involves a stress response and the participation of graft-i nfiltrating autoreactive T cells that operate under hsp-dependent mechanism s.