The regulation of macrophage activity in congenitally athymic mice.

It has been suggested that non-T cell-mediated cellular immune mechanisms might be elevated in nude mice, which could contribute to their partial resistance to intracellular infectious agents and to the development of spontaneous tumors. In this study we have examined macrophages (M phi) from athymic, euthymic and athymic T cell-reconstituted mice in terms of their phagocytic capacity, microbicidal and tumoricidal activity, and the production of hydrogen peroxidase and superoxide anions. These studies have demonstrated the presence of activated M phi in nude mice and suggest that this activation is associated with the absence of T cell-mediated suppression. We have also compared M phi activation levels in germ-free nude mice which have received a defined intestinal bacterial flora. We have found M phi activity to be significantly elevated in microbiologically defined nude mice when compared to germ-free nude mice, indicating that a resistant gut flora is capable of nonspecifically stimulating nude mouse M phi.