Researchers have observed a decline in symptomatic malaria with age and exposure to mosquitoes in a malaria endemic country. In spite of this individuals are still susceptible to asymptomatic Plasmodium falciparum (Pf) infection. CD4 T cells have been shown to be one of the major mediator of immunity to naturally acquired Pf infection and malaria vaccination. However, the exact role CD4 T cell mediated cytokine production and its association with malaria pathology remains poorly understood. Boyle et al. aimed to determine the cytokine profile Pf-specific CD4 T cell and determine what factors are associated with their function in children between the ages of 6 months to 10 years from highly malaria-endemic region.
Boyle et al. observed that children who were uninfected with no parasitemia had significantly higher frequencies of Pf-specific CD4 T cells with increased proportion of multifunctional (IFNg±IL-10±) cells than asymptomatic Pf infected children. This cytokine co-expression profile is postulated to reduce immunopathology at the expense of reduced parasite clearance. Boyle et al. observed that IL-10 producing CD4+ T cells had significantly higher levels of T-bet and BLIMP-1 (transcription factor responsible for IL-10 production) than classical IFNg and TNFa producing Th1 cells. Illustrating that IL-10 producing cells are not T-regs and are of Th1 origin.
Additionally, Boyle et al. also observed age related differences in T cell function, where an in increase in the frequency of IFN-g+ Pf-specific CD4 T cells and a decrease in IL-10+ Pf-specific CD4 T cells with an increase in children’s age. This was observed with concurrent decrease in parasite density with age. Suggesting a role of T cells in restricting parasite growth in these children, and preventing symptomatic disease.
In summary, Boyle et al. showed that CD4+ IL-10 producing Pf-specific T cells of Th1 origin are associated with reduced parasitemia in children from high malaria endemic countries. This suggests a role of IL-10+ Th1 T cells in natural immunity against symptomatic malaria infection.
Journal Article: Boyle, M.J. et al., 2017. The Development of Plasmodium falciparum-Specific IL10 CD4 T Cells and Protection from Malaria in Children in an Area of High Malaria Transmission. Frontiers in Immunology, 8, p.1. DOI: 10.3389/fimmu.2017.01329.
Article by Cheleka AM Mpande