Macrophage activation in murine African trypanosomiasis

African trypanosomiasis is accompanied by a profound general immunosuppression in which both suppressive T cells and macrophages (MΦ) have been implicated. The present studies define changes in the MΦ surface, endocytic and secretory properties, during the infection of mice by Trypanosoma brucei. Peritoneal MΦ obtained after the control of the first wave of parasitemia displayed characteristics similar to those activated by intracellular pathogens, such as Mycobacterium bovis bacillus Calmette-Guerin, e.g., the enhanced expression of Ia antigen, decreased MΦ-specific antigens, receptors mediating the pinocytosis of mannose-terminal glycoproteins, and an increased ability to secrete plasminogen activator, superoxide anion, and H₂O₂. Some markers of macrophage activation persisted during the subpatent period before the recurrence of parasitemia, whereas others reverted to normal. Mature T cell function appears not to be essential for MΦ activation by T. brucei since the infection of athymic nude mice also induced Ia antigens and plasminogen activator. These studies show that MΦ activated by different pathways express common features which may contribute to immune dysfunction observed in trypanosomiasis, as well as in other infections.