BackgroundFor a long time, the role of CD8+ T cells in blood-stage malaria was not considered important because erythrocytes do not express major histocompatibility complex (MHC) class I proteins. While recent evidences suggest that CD8+ T cells may play an important role during the erythrocytic phase of infection by eliminating parasites, CD8+ T cells might also contribute to modulate the host response through production of regulatory cytokines. Thus, the role of CD8+ T cells during blood-stage malaria is unclear. Here, we report the phenotypic profiling of CD8+ T cells subsets from patients with uncomplicated symptomatic P. vivax malaria.MethodsBlood samples were collected from 20 Plasmodium vivax-infected individuals and 12 healthy individuals. Immunophenotyping was conducted by flow cytometry. Plasma levels of IFN-¿, TNF-¿ and IL-10 were determined by ELISA/CBA. Unpaired t-test or Mann¿Whitney test was used depending on the data distribution.Results P. vivax-infected subjects had lower percentages and absolute numbers of CD8+CD45RA+ and CD8+CD45RO+ T cells when compared to uninfected individuals (p¿¿¿0.0002). A significantly lower absolute number of circulating CD8+CD45+CCR7+ cells (p¿=¿0.002) was observed in P. vivax-infected individuals indicating that infection reduces the number of central memory T cells. Cytokine expression was significantly reduced in the naïve T cells from infected individuals compared with negative controls, as shown by lower numbers of IFN-¿+ (p¿=¿0.001), TNF-¿+ (p¿<¿0.0001) and IL-10+ (p¿<¿0.0001) CD8+ T cells. Despite the reduction in the number of CD8+ memory T cells producing IFN-¿ (p¿<¿0.0001), P. vivax-infected individuals demonstrated a significant increase in memory CD8+TNF-¿+ (p¿=¿0.016) and CD8+IL-10+ (p¿=¿0.004) cells. Positive correlations were observed between absolute numbers of CD8+IL-10+ and numbers of CD8+IFN-¿+ (p¿<¿0.001) and CD8+TNF-¿+ T cells (p¿¿¿0.0001). Finally, an increase in the plasma levels of TNF-¿ (p¿=¿0.017) and IL-10 (p¿=¿0.006) and a decrease in the IFN-¿ plasma level (p <0.0001) were observed in the P. vivax-infected individuals.Conclusions P. vivax infection reduces the numbers of different subsets of CD8+ T cells, particularly the memory cells, during blood-stage of infection and enhances the number of CD8+ memory T cells expressing IL-10, which positively correlates with the number of cells expressing TNF-¿ and IFN-¿.