T cells from patients acutely infected with malaria exhibit a disease-related stimulation of DNA synthesis in response to Plasmodium falciparum antigen in vitro. This response is weak and short-lived, suggestive of induction of suppressor mechanisms. Exogenous T cell growth factor (IL 2) that was added to antigen-stimulated T cell cultures enhanced proliferation in antigen-responsive cultures, indicating that the lymphocytes expressed IL 2 receptors. In contrast, the addition of IL 2 to cultures that did not respond to antigen had no effect. Antigen-responsive cultures contained endogenous IL 2 as well, and the antigen-induced lymphocyte proliferation was correlated with IL 2 production. However, the results suggested that IL 2 production by the patients' T cells was insufficient or actively shut off, and that this was responsible for the premature cessation of their DNA synthesis. Supernatants from 60% of the T cell cultures treated with malaria antigen and from 30% treated with RBC ghost antigen contained interferon-gamma (IFN-gamma), as determined by a cytopathic effect inhibition assay combined with acid treatment and antibody neutralization or by an IFN-gamma-specific ELISA. There was no obvious correlation between antigen-induced lymphocyte proliferation and the presence of IFN-gamma in the culture supernatants. A high IFN-gamma activity was also seen in antigen-treated cultures from P. falciparum-immune donors living in highly endemic malaria areas. In contrast, no IFN-gamma was found in supernatants of antigen-treated T cells from healthy donors or patients with Plasmodium vivax malaria. Thus, the IFN-gamma activity of these cultures appears to reflect the presence of antigen-reactive T cells and may be useful as a sensitive indicator of cellular immunity in P. falciparum malaria.

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