Delayed Hypersensitivity to Toxoplasma and Unrelated Antigens in Toxoplasma -Infected Mice: Induction and Elicitation of Delayed-Type Hypersensitivity by Antigen-Pulsed Macrophages

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Abstract
Delayed-type hypersensitivity (DTH) to Toxoplasma and unrelated antigens in Toxoplasma-infected BALB/c mice was investigated by the radioisotopic uptake method of Vadas et al. DTH became positive on day 30 of infection and remained positive during chronic infection. The expression of DTH in mice infected with the relatively avirulent C37 strain of the parasite paralleled the Toxoplasma antibody response as detected by the Sabin-Feldman dye test. Mice sensitized with Toxoplasma, keyhole limpet hemocyanin or sheep erythrocytes during the acute or chronic phase of Toxoplasma infection showed a DTH reaction similar to that of uninfected sensitized controls. No parasite antigens [Ag] could be detected by immunofluorescence techniques on the surface of Toxoplasma-infected cells. When killed organisms were added to the cell cultures, specks of fluorescence appeared on cells containing intracellular parasites and on cells without intracellular organisms. The Ag may be present in or on macrophages in a form readily recognizable by T [thymus-derived] cells. Injection of uninfected normal macrophages pulsed with Toxoplasma-soluble Ag into the ears of chronically infected mice elicited a DTH reaction comparable to that observed when 106 formalin-fixed tachyzoites were used as the test Ag. When macrophages pulsed with Toxoplasma Ag were used to induce DTH in naive uninfected mice, the intensity of the reaction was similar to that observed in infected mice.