Macrophage Depletion Prior to Neospora caninum Infection Results in Severe Neosporosis in Mice

We observed that murine macrophages showed greater activation and increased interleukin 6 (IL-6), IL-12p40, and interferon gamma (IFN-) production duringNeospora caninum infection. Many macrophages migrated to the site of infection. Further-more, macrophage-depleted mice exhibited increased sensitivity toN. caninum infection. This study indicates that macrophages are required for achieving protective immunity againstN. caninum. Neospora caninum was first identified as a Toxoplasma gondii-like parasite that caused encephalomyelitis and myositis in dogs in Norway in 1984 (1). It was classified as a distinct species in 1988 (2). N. caninum is a cause of neosporosis, which leads to abortion, neonatal mortality, and congenital infection in cattle and neuromuscular pathology in dogs (3). The ability to survive infection is dependent upon interferon gamma (IFN-), the ma-jor mediator of resistance against N. caninum (4, 5). While IFN--producing CD4 and CD8 T cells are required for the acqui-sition of protective immunity against parasite infection (6), different types of innate cells may also exert distinct roles in achieving protective immunity. Generally, innate cells, such a