MACROPHAGES PRODUCE NITRIC-OXIDE AT ALLOGRAFT SITES

Objective The current study was designed to determine which cytokines produced during an alloimmune response stimulate macrophage nitric oxide (.N = O) production at allograft sites. Summary Background Data Previous work has demonstrated that rat sponge matrix allograft infiltrating cells produce more .N = 0 on stimulation with alloantigen than syngeneic graft infiltrating cells Addition of N(G)-monomethyl-L-arginine (NMA), an inhibitor of .N = O synthesis, promotes allospecific cytolytic T-lymphocyte effector function. Methods Polyurethane sponges were implanted subcutaneously in recipient Lewis rats and injected with 10 X 10(6) ACI splenocytes, On various days after grafting, graft-infiltrating cells were harvested tor in vitro study. Adherent macrophages from the graft infiltrating cell population were obtained by a 2- to 3-hour incubation to plastic dishes with subsequent washing to remove nonadherent cells. Results Stimulation of unseparated graft-infiltrating cel) populations with lipopolysaccharide or interferon-tau resulted in enhanced .N = 0 synthesis by allograft infiltrating cells compared with syngeneic graft-infiltrating cells, early after grafting. Macrophages recovered from an allograft site spontaneously produce more .N = 0 than macrophages recovered from syngeneic grafts (p < 0.001). Significantly enhanced levels of .N = 0 were produced by allograft macrophages compared with syngeneic graft macrophages on stimulation with lipopolysaccharide or interferon-tau (p less-than-or-equal-to 0.025). Conclusions Nitric oxide appears to be produced in response to the local cytokines secreted by an ongoing rejection reaction. Nitric oxide serves under these circumstances to modulate the alloimmune response.