Macrophages Produce Nitric Oxide at Allograft Sites

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Abstract
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 = O on stimulation with alloantigen than syngeneic graft-infiltrating cells. Addition of NG-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 108 ACI splenocytes. On various days after grafting, graft-infiltrating cells were harvested for 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 cell populations with lipopolysaccharide or interferon-r resulted In enhanced •N = O synthesis by allograft infiltrating cells compared with syngeneic graft-infiltrating cells, early after grafting. Macrophages recovered from an atlograft site spontaneously produce more •N = O than macrophages recovered from syngeneic grafts (p ≤ 0.001). Significantly enhanced levels of •N = O were produced by allograft macrophages compared with syngeneic graft macrophages on stimulation with lipopolysaccharide or interferon-r (p ≤ 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.