Association of Early Interferon‐γ Production with Immunity to Clinical Malaria: A Longitudinal Study among Papua New Guinean Children

Abstract

Background. Elucidating the cellular and molecular basis of naturally acquired immunity to Plasmodium falciparum infection would assist in developing a rationally based malaria vaccine. Innate, intermediate, and adaptive immune mechanisms are all likely to contribute to immunity. Interferon-γ (IFN-γ) has been implicated in both protection against and the pathogenesis of malaria in humans. In addition, considerable heterogeneity exists among rapid IFN-γ responses to P. falciparum in malaria-naive donors. The question remains whether similar heterogeneity is observed in malaria-exposed individuals and whether high, medium, or low IFN-γ responsiveness is differentially associated with protective immunity or morbidity. Methods. A 6-month longitudinal cohort study involving 206 school-aged Papua New Guinean children was performed. Peripheral blood mononuclear cells collected at baseline were exposed to live P. falciparum–infected erythrocytes. Early IFN-γ responses were measured, and IFN-γ–expressing cells were characterized by flow cytometry. IFN-γ responsiveness was then tested for associations with parasitological and clinical outcome variables. Results. Malaria-specific heterogeneity in early IFN-γ responsiveness was observed among children. High-level early IFN-γ responses were associated with protection from high-density and clinical P. falciparum infections. Parasite-induced early IFN-γ was predominantly derived from γδ T cells (68% of which expressed the natural killer marker CD56) and αβ T cells, whereas natural killer cells and other cells made only minor contributions. The expression of CD56 in malaria-responsive, IFN-γ–expressing γδ T cells correlated with IFN-γ responsiveness. Conclusions. High, early IFN-γ production by live parasite–stimulated peripheral blood mononuclear cells is a correlate of immunity to symptomatic malaria in Papua New Guinean children, and natural killer–like γδ T cells may contribute to protection.