Adaptive Immune Responses Mediated Age-related Plasmodium yoelii 17XL and 17XNL Infections in 4 and 8-week-old BALB/c Mice

Background: As the quest to eradicate malaria continues, it is important to clarify the opposite clinical outcomes between childhood and adulthood. The relationship between adaptive immune response and age-related malaria infection remains unknown. Methods 4 and 8-week-old mice were used to mimic childhood and adulthood, respectively. Parasitemia and the survival rate were monitored. The proportion and function of Th1 and Th2 cells were detected by FACS. The levels of IFN-γ, IL-4, total IgG, IgG1, IgG2a and Plasmodium yoelii MSP-1-special IgG were measured by ELISA. Results Infant mice were more susceptible to P. yoelii 17XNL infection, with lower survival rate and higher parasitemia. The adult group showed greater resistance to P. yoelii 17XL infection, with lower parasitemia. Compared with 4-week-old mice, the percentage of CD4 + T-bet + IFN-γ + Th1 cells as well as IFN-γ production were significantly increased on day 5 p.i. in the 8-week-old mice after P. yoelii 17XNL infection. The percentage of CD4 + GATA3 + IL-4 + Th2 cells and CD4 + CXCR5 + Tfh cells, and IL-4 production in the 8-week-old mice obviously increased on day 5 and day 10 after P. yoelii 17XNL infection. Notably, the levels of total IgG, IgG1, IgG2a and P. yoelii MSP-1-special IgG were also significantly increased in the 8-week-old mice. PD-1, a marker of exhaustion, was up-regulated on CD4 + or activated CD4 + T cells in the 8-week-old mice as compared to the 4-week-old group. Conclusion We consider that enhanced cellular and humoral adaptive immunity might contribute to rapid clearance of malaria among adults, likely in a PD-1-dependent manner due to induction of CD4 + T cells exhaustion.