Longitudinal analysis of gamma delta T cell subsets during malaria infections in Malian adults

BACKGROUND: Immunity that limits malarial disease is acquired over time, but adults living in endemic areas continue to become infected and can require treatment for clinical illness. Gamma delta (γδ) T cells, particularly the Vδ2+ subset, have been associated with development of clinical malaria in children. In this study, the dynamics of total γδ T cells, Vδ2+ and Vδ2- T cells were measured during a malaria transmission season in Malian adults. METHODS: This study explored γδ T cell dynamics and Plasmodium falciparum infection outcomes over the course of the malaria transmission season in Malian adults enrolled in the placebo arm of a double-blind randomized vaccine trial. All volunteers were treated with anti-malarial drugs prior to the start of the transmission season and blood smears were assessed for P. falciparum infection every 2 weeks from July 2014 to January 2015. The study participants were stratified as either asymptomatic infections or clinical malaria cases. Vδ2+ and Vδ2- γδ T cell frequencies and activation (as measured by CD38 expression) were measured in all study participants at baseline and then every 2 months using a whole blood flow cytometry assay. RESULTS: Forty of the forty-three subjects became infected with P. falciparum and, of those, 21 individuals were diagnosed with clinical malaria at least once during the season. The γδ T cell percentage and activation increased over the duration of the transmission season. Both the Vδ2+ and Vδ2- γδ T cells were activated by P. falciparum infection. CONCLUSION: γδ T cells increased during a malaria transmission season and this expansion was noted in both the Vδ2+ and Vδ2- γδ T cells. However, neither expansion or activation of either γδ T cell subsets discriminated study participants that had asymptomatic infections from those that had clinical malaria cases.