Circulating immune complexes in toxoplasmosis: detection and clinical correlates

The 125I-C1q binding test was employed to detect circulating immune complexes in serum of 27 subjects with acute toxoplasmosis. The subjects had no known underlying disease. Elevated C1q binding activity (C1q-BA) was found in the serum of each of three adults with the systemic febrile form of toxoplasmosis, seven of 19 patients with the lymphadenopathic form, and one of four infants with congenital infection. The patients with the systemic form of illness had significantly greater mean C1q-BA than did those with the lymphadenopathic form (P less than 0.001). In six episodes of symptomatic toxoplasmosis associated with elevated C1q-BA, follow-up sera were obtained after resolution of all signs and symptoms. Each of these sera showed normalization of C1q-BA. We conclude that immune complex like material is frequently present in the serum of patients with toxoplasmosis and parallels disease activity.