Invasion of the guinea pig conjunctiva by Toxoplasma gondii

Although interactions of Toxoplasma gondii with host cells have been studied extensively in vitro, relatively little is known about the initial interactions of Toxoplasma with mucosal surfaces in vivo. We therefore studied the onset of a Toxoplasma infection in guinea pig conjunctiva. Toxoplasma were inoculated onto the conjunctival epithelium. The tissue was fixed 15 min to 48 hr after inoculation and examined by electron microscopy. Guinea pigs similarly inoculated were maintained in the laboratory for 2 to 8 weeks and tested for antibody by the Toxoplasma dye test. We found that parasites invaded both epithelial and goblet cells within minutes of inoculation. Replication occurred within 4 hr of inoculation and took place mainly in epithelial cells. Within 48 hr, the organisms were found beneath the basal lamina of the epithelium. The host developed an inflammatory response consisting first largely of polymorphonuclear leukocytes and later largely of macrophages. The parasites also replicated in macrophages, showing their ability to evade host defenses in nonimmune animals. Inoculated guinea pigs kept in the laboratory for 8 weeks survived and developed elevated antibody titers against Toxoplasma. The guinea pig conjunctiva is a suitable tissue for studying the pathogenesis of toxoplasmosis.