Phenotype and localization of macrophages expressing inducible nitric oxide synthase in rat hepatic allograft rejection.

BACKGROUND

We investigated the phenotype and localization of macrophages expressing inducible nitric oxide synthase (iNOS) in rat hepatic allografts, using double immunostaining with anti-macrophage iNOS (macNOS) and rat anti-macrophage (ED1 or ED2) monoclonal antibodies.

METHODS

The animals were divided into three experimental groups: group 1, isografts; group 2, untreated hepatic allografts; and group 3, hepatic allografts treated with FK506.

RESULTS

Plasma nitrite/nitrate concentrations in group 2 increased on day 3, peaked on day 5, and decreased thereafter. In contrast, the plasma nitrite/nitrate concentrations in group 1 increased slightly on day 3, but decreased gradually thereafter. The plasma concentrations of nitrite/nitrate did not vary in group 3. The peak nitrite/nitrate values in group 2 were significantly greater than those in groups 1 and 3. The number of macNOS+ cells peaked on day 5 in group 2. In contrast, a few macNOS+ cells were seen in the liver grafts of groups 1 and 3. Double immunostaining revealed that the macNOS+ cells consisted of macNOS+ ED1+ (80%) and macNOS+ ED2+ (40%) in the untreated hepatic allografts on day 5. In addition, a number of macNOS+ cells also were seen in the red pulp of the recipient spleen in the untreated hepatic allografts.

CONCLUSIONS

These results suggest that the intense iNOS expression by the monocyte/macrophage lineage among the hepatic infiltrates and by the splenic macrophages after transplantation supports a role for nitric oxide in the immunomodulation of allogeneic responses in local and remote organs, and possibly serves as a mediator of cytotoxic graft damage.