Retinal vasculitis in ocular toxoplasmosis in nonhuman primates

Six monkeys had prior systemic immunization followed by intraretinal challenge to each eye with Toxoplasma antigens. All eyes developed iridocyclitis, vitritis, and retinal edema, but no necrotizing retinochoroiditis. One-half of the eyes were then challenged with living organisms and the other one-half with Toxoplasma antigens. All eyes developed iridocyclitis, vitritis, and retinal edema, but no necrotizing retinochoroiditis. Four months later, the right eye of each monkey was challenged with living Toxoplasma organisms injected intraretinally. Each injected eye developed iridocyclitis, vitritis, and retinal edema 24 hours after injection, and all developed a retinal vasculitis 6 days after injection. One injected eye developed a papillitis. A subcutaneous booster of living Toxoplasma organisms in four of the monkeys failed to produce a reactivation of the iridocyclitis, vitritis, and vasculitis. These findings suggest that hyperimmunization provides protection against the development of a necrotizing toxoplasmic retinochoroiditis in nonhuman primates and that it may lead to retinal vasculitis and iridocyclitis. This study also serves as an animal model of retinal vasculitis in ocular toxoplasmosis.