Long-Lived CD4+IFN-γ+ T Cells rather than Short-Lived CD4+IFN-γ+IL-10+ T Cells Initiate Rapid IL-10 Production To Suppress Anamnestic T Cell Responses during Secondary Malaria Infection.

CD4 ⁺ T cells that produce IFN-γ are the source of host-protective IL-10 during primary infection with a number of different pathogens, including Plasmodium spp. The fate of these CD4 ⁺ IFN-γ ⁺ IL-10 ⁺ T cells following clearance of primary infection and their subsequent influence on the course of repeated infections is, however, presently unknown. In this study, utilizing IFN-γ-yellow fluorescent protein (YFP) and IL-10-GFP dual reporter mice, we show that primary malaria infection-induced CD4 ⁺ YFP ⁺ GFP ⁺ T cells have limited memory potential, do not stably express IL-10, and are disproportionately lost from the Ag-experienced CD4 ⁺ T cell memory population during the maintenance phase postinfection. CD4 ⁺ YFP ⁺ GFP ⁺ T cells generally exhibited a short-lived effector rather than effector memory T cell phenotype postinfection and expressed high levels of PD-1, Lag-3, and TIGIT, indicative of cellular exhaustion. Consistently, the surviving CD4 ⁺ YFP ⁺ GFP ⁺ T cell-derived cells were unresponsive and failed to proliferate during the early phase of secondary infection. In contrast, CD4 ⁺ YFP ⁺ GFP ^- T cell-derived cells expanded rapidly and upregulated IL-10 expression during secondary infection. Correspondingly, CD4 ⁺ T cells were the major producers within an accelerated and amplified IL-10 response during the early stage of secondary malaria infection. Notably, IL-10 exerted quantitatively stronger regulatory effects on innate and CD4 ⁺ T cell responses during primary and secondary infections, respectively. The results in this study significantly improve our understanding of the durability of IL-10-producing CD4 ⁺ T cells postinfection and provide information on how IL-10 may contribute to optimized parasite control and prevention of immune-mediated pathology during repeated malaria infections.
(Copyright © 2016 The Authors.)