Involvement of macrophages in genetic resistance to bone marrow grafts. Studies with two specific antimacrophage agents, carrageenan and silica.

Carrageenans and silica, agents toxic for macrophages, were used in this study to examine the role of macrophages in resistance of irradiated mice to inbred parental and rat bone marrow grafts. Administration of 2.5 mg of carrageenans or 2.5-5 mg of silica particles intravenously to prospective graft recipients resulted in a prompt abrogation of hybrid and xenogeneic resistance. The macrophage stabilizer poly-2-vinylpyridine N-oxide (PVNO) injected subcutaneously in the dose of 150 mg/kg, 24 hr before silica prevented or reduced the suppression of resistance. PVNO, however, did not antagonize the suppression of resistance by carrageenen, horse anti-mouse thymocyte serum and cyclophosphamide. These results suggest that a) a subpopulation is involved in marrow graft rejection by irradiated mice; b) carrageenan and silica apparently act on macrophages by different mechanisms c) horse anti-mouse thymocyte serum and cyclophosphamide may act on cells other than macrophages or they act on macrophages by a different mechanism than silica, to resistance to bone marrow transplantation.