HEAT SHOCK PROTEIN EXPRESSION AND T-CELL REACTIVITY IN RAT CARDIAC ALLOGRAFTS UNDERGOING CHRONIC REJECTION

Abstract

155 Chronic rejection reflects a continuous, low-grade inflammatory response to tissue injury initiated by alloimmune mechanisms. During this process, the allograft undergoes a stress response which alters the expression of heat shock proteins (hsp) and activates immune mechanisms involving hsp. This concept has been studied with a rat cardiac allograft model in recipients pretreated with donor bone marrow cells. Chronic rejection is manifested by obliterative arteriopathy and endocardial infiltrates of lymphocytes. Pretreatment with a liver allograft is associated with an absence of these lesions in the transplanted heart. Hsp expression was determined by immunohistology with monoclonal antibodies to mammalian hsp60, the inducible hsp72, the constitutively expressed hsc73, and the grp78 C-terminal sequence KSEKDEL (grp78seq) (all from StressGen, Victoria, BC). Myocyte expression of hsp60 and hsc73 was higher in allografts with chronic rejection especially in areas of lymphoid infiltration. The inflammatory infiltrates of obliterated blood vessels contained clusters of grp78seq-positive cells resembling dendritic cells rather than lymphocytes. Many grp78seq-positive cells were also seen between the mural surface and the endocardial and epicardial lymphocytic infiltrates. Grafts without chronic rejection contained very few grp78 seq-positive cells. During chronic rejection, the spleen showed increased numbers of grp78seq-positive cells in the marginal zones of the periarterial lymphatic sheaths in spleens. The marginal zones contain dendritic macrophages and lymphocytes and represent a major site for antigen uptake and processing. In lymph nodes, many grp78seq-positive cells were present in the subcortical areas and the medullary cords but not in the cortical regions of the lymphoid follicles and germinal centers. Culturing of graft-infiltrating cells with mycobacterial hsp71 and IL-2 yielded lymphocyte lines without alloreactivity, but with strong proliferative responsiveness to self-APC, but only in the presence of mycobacterial hsp71 or murine grp78. These data show the presence of grp78-dependent, autoreactive T-lymphocytes and grp78seq-positive dendritic like cells in the cellular infiltrates of chronically rejecting allografts. They provide further support the concept that the pathogenesis of chronic rejection involves a stress response and the participation of autoreactive lymphocytes that operate under mechanisms involving heat shock proteins.