Ia-bearing macrophages in athymic mice: antigen presentation and regulation.

Ia-bearing macrophages from spleens and peritoneal cavities of athymic (nu/nu) and euthymic (nu/+) were compared. Macrophages from both strains of mice had equal antigen-presenting ability. The basal numbers of unstimulated Ia-bearing peritoneal macrophages were equal, but only euthymic mice recruited large numbers of Ia-bearing macrophages after Listeria infection. The i.p. injections of a "macrophage Ia-recruiting factor" induced exudates rich in Ia-bearing macrophages in both athymic and euthymic mice. These data suggest 2 levels of control of Ia-bearing macrophages: a basal T cell-independent level and a stimulated level dependent on mature T cells.