Identification of IL 2R+ T cells and macrophages within rejecting rat cardiac allografts, and comparison of the effects of treatment with anti-IL 2R monoclonal antibody or cyclosporin.

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Abstract
Monoclonal antibodies to lymphokine-induced activation antigens of lymphocytes and macrophages were used to analyze the intragraft events occurring during acute rejection of rat heterotopic cardiac allografts. The cells present during untreated rejection were then compared with those present in situ after immunosuppression with the mouse anti-rat IL 2 receptor (anti-IL 2R) monoclonal antibody ART-18 or cyclosporin (CsA). Untreated rats rejected their grafts within 7 days, whereas rats receiving 10 days of i.v. ART-18 antibody therapy showed graft prolongation to more than 21 days, and rats receiving CsA for 7 days maintained their grafts indefinitely. Untreated rejection was associated with an influx of T (W3/13+) cells and macrophages (ED-1+, ED-2+). Activated mononuclear cells (IL 2R+) were identified within rejecting grafts from day 2, and their numbers peaked on days 4 to 6 when 15 to 20% of infiltrating leukocytes were IL 2R+. Double labeling studies of IL 2R+ cells present at day 6 showed surprisingly that both T cells and macrophages expressed IL 2R. In particular, although 55.8 +/- 6.9% (mean +/- SD) of IL 2R+ cells expressed the pan-T cell antigen 3/13, a similar proportion of IL 2R+ cells (49.8 +/- 8.2%) expressed the macrophage antigen ED-2. Conversely, both T cells and macrophage populations showed heterogeneity in their expression of IL 2R, because 39.2 +/- 12.2% of T cells and 31.0 +/- 13.4% of macrophages were IL 2R+. In addition, inflammatory macrophages at day 6 expressed the A1-3 antigen. Expression of this antigen by macrophages has previously been linked with development of macrophage procoagulant activity, and in this model intragraft inflammatory macrophages were closely associated with widespread deposits of fibrin. By comparison with untreated animals, rats treated with either ART-18 or CsA both lacked detectable IL 2R+ cells during the first 14 days post-transplantation (post-Tx), and showed significantly less cellular infiltration. However, although grafts of CsA-treated animals continued to remain IL 2R- and failed to stain with the macrophage activation marker A1-3, ART-18-treated rats showed increasing infiltration by both IL 2R+ mononuclear cells and A1-3+ macrophages, as well as increasing perivascular and interstitial fibrin deposition, prior to rejection by day 22. These studies document the presence of small number of activated intragraft T cells and macrophages during rat cardiac rejection, and show how CsA, and to a lesser extent anti-IL 2R therapy, inhibit this in situ activation and prolong graft survival. (ABSTRACT TRUNCATED AT 400 WORDS)