REGULATION OF ENDOTHELIAL VCAM-1 EXPRESSION IN MURINE CARDIAC GRAFTS - ROLES FOR TNF AND IL4

The in vivo mechanisms of vascular endothelial activation and VCAM-1 e xpression were studied in murine heterotopic cardiac grafts. Prelimina ry studies demonstrated that cardiac allograft endothelia develop reac tivity with MECA-32 monoclonal antibody (MAb) and M/K-2 (anti-VCAM-1) MAb within 3 days of transplantation, whereas cardiac isografts develo p MECA-32 reactivity but no M/K-2 reactivity. Additional studies demon strated that a single treatment of cardiac isograft recipients with th e anti-CD3 MAb 145s-2C11 induces VCAM-1 expression on isograft microva scular endothelia within 24 hours. We have used this experimental syst em to identify the cytokines responsible for expression of VCAM-1 and MECA-32 MAb reactivity on graft vascular endothelia. We report that th e expression of VCAM-1 on isograft endothelia that was induced with an ti-CD3 MAb was blocked by simultaneous treatment with either pentoxify lline, soluble tumor necrosis factor (TNF) receptor (TNFR:Fc), anti-IL 4 MAb, or soluble IL4R, but not by anti-IFN-gamma MAb. Alternatively, a similar pattern of isograft endothelial VCAM-1 expression was stimul ated in the absence of anti-CD3 MAbs with a single injection of human recombinant TNF-alpha, or with recombinant murine IL4 provided as IL4/ anti-IL4 MAb complexes. In addition, the IL4-induced VCAM-1 expression was completely blocked by a single intravenous treatment of the isogr aft recipients with TNFR:Fc. This suggests that high concentrations of TNF-alpha can stimulate endothelial VCAM-1 expression, but these conc entrations are apparently not achieved in cardiac isografts, In the ab sence of an inducing agent such as anti-CD3 MAb, the stimulation of VC AM-1 expression with exogenous IL4 may reflect functional interaction between endogenous TNF and exogenous IL4, as suggested by the blocking experiments with TNFR:Fc. Although cardiac isograft endothelia normal ly develop reactivity with MECA-32 MAb within 3 days of transplantatio n, treatment of cardiac isograft recipients with anti-CD3 MAb accelera ted MECA-32 reactivity to within 24 hours of transplantation This acce lerated expression can be experimentally manipulated in the same way a s M/K-2 reactivity, suggesting that similar mechanisms may control the development of these two inflammatory endothelial phenotypical marker s, despite their differential expression in cardiac isografts and allo grafts.