Inducible nitric oxide synthase in innate immune cells is important for restricting cyst formation of Toxoplasma gondii in the brain but not required for the protective immune process to remove the cysts.

Significantly larger numbers of Toxoplasma gondii cysts were detected in the brains of RAG1-/-NOS2-/- than RAG1-/- mice following infection. In contrast, the cyst numbers markedly decreased in a same manner in both strains of mice after receiving CD8+ immune T cells. Thus, NOS2-mediated innate immunity is important for inhibiting formation of cysts in the brain but not required for the T cell-initiated cyst removal, which is associated with phagocyte accumulation. Treatment with chloroquine, an inhibitor of endolysosomal acidification, partially but significantly inhibited the T cell-mediated cyst removal, suggesting that phagosome-lysosome fusion could be involved in the T. gondii cyst elimination.