Pathogenesis of Trypanosoma brucei infection in deer mice (Peromyscus maniculatus). V. Macrophage ultrastructure and function.

Macrophage numbers increased in the spleen, liver, testes, heart, and kidney of deer mice infected for seven to ten weeks with Trypanosoma brucei EATRO 110. The macrophages were activated as indicated by their increased size and significant increases in numbers of cell organelles including profiles of rough endoplasmic reticulum (which also increased in length), mitochondria, primary and secondary lysosomes, bundles of Golgi's apparatus, and free lysosomes compared to macrophages from control mice. Some macrophages representing epithelioid cells have even greater numbers of organelles than the activated macrophages and had interdigitation in some locations, such as the heart, but with minimal phagocytic activity. These epithelioid cells were present in the kidney, testes, and particularly in the heart of infected mice. Few cardiac macrophages had finely granular deposits on their nuclear membrane. The activated macrophages had enhanced phagocytosis of trypanosomes, red blood cells, neutrophils, eosinophils, lymphocytes, and plasma cells. In addition to phagocytosis, another probable consequence of macrophage activation may be depression of lymphocyte function. Phagocytosis of trypanosomes by neutrophils also was encountered occasionally.