Cyclosporine and anti-interleukin 2 receptor monoclonal antibody therapy suppress accelerated rejection of rat cardiac allografts through different effector mechanisms.

Increasing numbers of sensitized patients are either precluded from receiving an allograft or experience accelerated rejection which may be refractory to conventional therapy. Using a rat model, we have shown that accelerated (24 hr) rejection of LBN cardiac Tx in LEW rats sensitized with BN skin grafts 7 days earlier, could be prevented by treatment with cyclosporine (15 mg/kg/day x7 days, Tx survival about 42 days) or ART-18, an anti-IL-2R mAb (300 micrograms/kg/day x10 days i.v., Tx survival about 16 days). In this study, we evaluated intragraft mechanisms responsible for these effects by immunoperoxidase localization of relevant humoral mediators (IgG, IgM, C3, cross-linked fibrin), graft infiltrating cells (GIC), and associated cytokines (IL-2, IFN-g, tumor necrosis factor [TNF], or cytokine receptors (IL-2R). Tx rejected in fulminating fashion by 24 hr in sensitized hosts showed extensive and progressive endothelial deposition of IgG, C3, and fibrin from 2 hr, followed by an influx of neutrophils at 3 hr, and peak numbers of GIC by 18 hr (88.8 +/- 20.3 leukocytes/field). At 18 hr, GIC consisted of neutrophils (26%), T cells (20%, greater than 90% of which were OX-8+), and monocytes/macrophages (53%), whereas B cells were absent. By 18 hr, up to 20% of GIC were IFN-g+, 10% were IL-2R+, and 10% were IL-2+, consistent with labeling of 20% of cells with OX-22. Widespread endothelial and mononuclear cell labeling for TNF and the procoagulant molecular tissue factor (TF) were also noted. In contrast to untreated grafts, CsA treatment essentially abolished intragraft Ig, C3, and fibrin deposition. Moreover, despite dense cell infiltration at 24 hr (total GIC 55.3 +/- 13.4/field), analysis of CsA-treated Tx showed markedly decreased neutrophils (0.5%), with increased T cells (35%) and similar proportions of macrophages (66%). In addition to the reduction in neutrophils, Ig and C3, fewer IL-2R+ (6%) and OX-22+ (3%) cells, considerably less TNF and TF, and almost no IL-2+ or IFN-g+ GIC (less than 1%) were detected. Surprisingly, ART-18 treatment also greatly decreased but did not abolish endothelial deposition of C3, IgG, or IgM, whereas widespread endothelial and mononuclear labeling for fibrin, TNF, and TF remained. In addition, GIC (about 54.8 +/- 16.1/field) contained only moderately reduced numbers of neutrophils (31%) and the proportions of T cells (27%) and macrophages (49%) were generally comparable to those of rejecting Tx in untreated rats.(ABSTRACT TRUNCATED AT 400 WORDS)