The role of mononuclear phagocytes in cardiac allograft rejection in the rat: I. Ultrastructural and cytochemical features

Abstract

Mononuclear phagocytes (MNP) have been identified in rejecting rat cardiac allografts by morphological and cytochemical criteria. Their accumulation has been quantitated and their distribution within the graft recorded. Lymphocytes were the major infiltrating cell type present 3 days after transplantation, but by Day 5 and Day 7 there were 2.5 to 3 times as many MNP as lymphocytes. In the later stages (Days 6 and 7) many MNP were closely adjacent to myocardial cells and frequently possessed pseudopodia which were indenting the myocardial cell membrane. Allograft recipients given 750 rads γ-irradiation and reconstituted with thoracic duct lymphocytes rapidly rejected the graft. As many MNP were present in such grafts as in unmodified recipients. A potent antimacrophage serum did not prolong graft survival or alter the numbers of MNP within rejecting grafts. We conclude that MNP must be considered strong candidates for effector cells in allograft rejection and that satisfactory depletion techniques for MNP are not yet available.