Monocytes mediate mucosal immunity to Toxoplasma gondii.

Toxoplasma gondii is a widespread protozoan parasite that causes water and foodborne infections in humans. The parasite not only infects intestinal enterocytes but also spreads by migration across the epithelial layer and entry into the submucosa. Within the lamina propria, innate immune responses lead to initial parasite control, although the infection disseminates widely and persists chronically despite adaptive immunity. Inflammatory monocytes exit the bone marrow and home to the lamina propria where they express antimicrobial effector functions that control infection. Ablation of the signals for recruitment of inflammatory monocytes in the mouse results in uncontrolled parasite replication, extensive infiltration of neutrophils, intestinal necrosis, and rapid death. Inflammatory monocytes play a pivotal role in mucosal immunity against T. gondii, and likely other enteric pathogens.