IA antigen-positive epithelioid cells in experimentally induced granulomatous inflammation

Abstract

IA antigens on the cell membrane of inflammatory macrophages and epithelioid cells were investigated with immunoelectron microscopic method during development of granulomas induced by subcutaneous inoculation of 10 7 Mycobacterium lepraemurium into mice with and without hypersensitivity. In C57BL 6N (H-2 b immunogenetic high responder mice 6 weeks after infection majority (87%) of infiltrated cells were IA-positive. Two types of the staining reaction, strong and weak reactivity, were recognized among the positive cells. Strongly IA-positive cells showed lower phagocytosis (0.9/cell section) of mycobacteria than the weakly reacted cells (4.9/cell section). The strongly positive cells underwent morphological differentiation into large epithelioid cells during development of the hypersensitivity-type murine lepromas after 10 or more weeks of infection. Types of granulomas and IA-positive cells in C57BL 6N (nu/+) mice were identical to those found in C57BL 6N . In C57BL 6N ( nu nu ) athymic nude mice initial infiltrating cells contained 38% of weakly IA-positive macrophages and a small number (7%) of strongly IA-positive macrophages. But the reactivity was lost later and only 4% of IA-positive cells remained in the granulomas without hypersensitivity. CBA J (H-2 k) low responder mice did not show IA-positive cells in either initial or late stage during the development of nonhypersensitivity-type murine lepromas. We suggest that the presence of IA-positive cells, particularly IA-positive epithelioid cells, in the lesions modulates the course of granulomatous tissue reaction in murine lepromas.