RAPAMYCIN TREATMENT DEPRESSES INTRAGRAFT EXPRESSION OF KC MIP-2, GRANZYME-B, AND IFN-GAMMA IN RAT RECIPIENTS OF CARDIAC ALLOGRAFTS

Rapamycin (RPM) treatment prevents accelerated rejection of cardiac al lografts in sensitized rats. The prominent feature of this brisk 24-h rejection, which includes a panoply of both cellular and humoral host immune responses, is a massive infiltration of rejecting grafts with n eutrophils. In this study we tested the hypothesis that RPM-mediated t herapeutic effects on accelerated rejection may be linked to decreased expression of protein encoded by gro/melanoma-growth stimulatory acti vity gene (KC) and macrophage inflammatory protein-2 (MIP-2) genes, th e operational rat homologues of the human intercrine-alpha cytokines w ith proinflammatory IL-8-like neutrophil activation/chemotactic proper ties. The induction of these genes was then correlated with mRNA profi les encoding for Th1-selective IFN-gamma and CTL-specific granzyme B p roteins. Northern blot analysis of RNA from cardiac allografts of sens itized untreated recipients, revealed maximal levels of KC and MIP-2 m RNA at 3 to 6 h after transplantation. In contrast, IFN-gamma mRNA, wh ich was at most very weakly expressed at 3 h, peaked between 6 to 12 h . As with IFN-gamma, granzyme B transcripts were undetectable at 3 h, but peaked around the time of actual graft rejection at 24 h. RPM ther apy abrogated accelerated rejection and prolonged cardiac allograft su rvival to ca. 46 days. This effect was associated with markedly reduce d expression of KC and MIP-2 mRNA in the first 24 h as well as at 7 an d 34 days after transplantation. Moreover, RPM completely blocked intr agraft appearance of granzyme B and IFN-gamma mRNA in long term cardia c allografts. Immunohistologic analysis has revealed that accelerated rejection was associated with extensive neutrophil infiltration, which peaked at 18 to 24 h. At this time, leukocytes and endothelium were i ntensely stained for IL-8 and IFN-gamma antibodies. In contrast, the a llografts from RPM-treated hosts showed essentially no neutrophil infi ltration and minor, focal staining for IL-8 and IFN-gamma. This study demonstrates an association between the early expression of genes for proinflammatory IL-8-dependent neutrophil chemotactic activity, and la ter expression of genes associated with activation/effector activity o f CTL and NK cells. It also documents a novel effect of RPM in vivo, w hich results in the suppression of intragraft IL-8-like and CTL-depend ent mRNA/protein production and diminished neutrophil infiltration; th ese may contribute to the striking efficacy of RPM therapy in sensitiz ed graft recipients.