CD4(+)CD25(+)Foxp3(+) regulatory T cells prevent the development of Th1 immune response by inhibition of dendritic cell function during the early stage of Plasmodium yoelii infection in susceptible BALB/c mice

Protective immunity against murine malaria infection depends largely on the establishment of effective Th1 immune response during the early stages of infection. Experimental data suggest that the death of Plasmodium yoelii 17XL (P.y 17XL) susceptible BALB/c mice results from the suppression of Th1 immune response mediated by CD4(+)CD25(+)Foxp3(+) regulatory T cells (Tregs). However, the mechanism by which Tregs regulate Th1 immune response is poorly understood. Since immunity is initiated by dendritic cells (DCs), we analysed DC responses to P.y 17XL in control and Treg-depleted BALB/c mice. Myeloid DC proliferation, phenotypic maturation and interleukin-12 (IL-12) production were strongly inhibited in control BALB/c mice. In contrast, plasmacytoid DC proliferation and IL-10 production were strongly enhanced in control BALB/c mice. In-vivo depletion of Tregs resulted in significantly reversed inhibition of DC response, which may contribute to the establishment of Th1 immune response, indicating that Tregs contribute to the suppression of Th1 immune response during malaria. These findings suggest Tregs contribute to prevent Th1 immune response establishment during the early stage of P.y 17XL infection by inhibiting DC response.