Different clinical forms of Plasmodium vivax infection result in unique T cell epitope-specific immune responses.

Malaria remains a significant public health concern despite a steady decline in symptomatic cases. In Brazil, endemic regions are primarily concentrated in the Amazon region, where most cases are attributed to Plasmodium vivax. Although malaria does not confer long-term sterilizing immunity, clinical immunity is achieved, leading to asymptomatic (ASY) infections. Assessing cellular immunity against P. vivax is challenging due to the lack of well-defined antigens. Hence, we developed a library of 310 P. vivax peptides (MPv310) to evaluate antigen-specific responses of CD4+ T cells and their memory subpopulations. The specific cytokine response, IFN-γ and TNF, and upregulation of activation markers, CD69 and CD154, were assessed in P. vivax-infected individuals, including symptomatic before treatment (SY-I) patients, symptomatic after treatment (SY-T) patients, ASY individuals, and uninfected individuals. CD4+ T cells were stimulated with peptides and analyzed by flow cytometry or ELISpot. MPv310 stimulation led to increased frequencies of CD154+ and CD69+CD154+ cells in symptomatic before treatment and SY-T patients and IFN-γ+TNF+ cells in SY-T patients. Cytokine response was also associated with ASY status, with higher frequencies of IFN-γ+TNF+ among CD4+ T cells and of IFN-γ+ in the effector memory subset. Distinct antigen-specific activation patterns were also observed among symptomatic and ASY individuals when the peptide pool was divided into smaller pools representing specific antigens. This study reveals that MPv310 and different sets of minipools stimulate CD4+ T cells in symptomatic and ASY infections, having potential to be used as a new tool to assess immune mechanisms associated with different clinical presentations of the disease and protection against malaria.