Serum interferon activity of patients with leishmaniasis.

Serum from a significant proportion of 29 cutaneous and 12 mucocutaneous leishmaniasis patients exhibited interferon activity in a cytopathic assay: positive tests were obtained for 24.1% and 41.7% of the patients, respectively. Similar positive frequencies were observed in other parasitic diseases (schistosomiasis, 12.5%; toxoplasmosis, 20%; Chagas' disease, 16%; leprosy, 12.5%; tuberculosis, 30%). In contrast, none of the 44 serum samples from American visceral leishmaniasis (AVL) patients had interferon activity during the active stage of the disease. However, 13% of the samples obtained from patients recovered from AVL were positive.