Modulation of experimental blood stage malaria through blockade of the B7/CD28 T-cell costimulatory pathway

Recent studies have implicated cytokines associated with CD4+ T lymphocytes of both T helper (Th)1 and Th2 subsets in resistance to experimental blood stage malaria. As the B7/CD28 costimulatory pathway has been shown to influence the differentiation of Th cell subsets, we investigated the contribution of the B7 molecules CD80 and CD86 to Th1/Th2 cytokine and immunoglobulin isotype profiles and to the development of a protective immune response to malaria in NIH mice infected with Plasmodium chabaudi. Effective blockade of CD86/CD28 interaction was demonstrated by elimination of interleukin (IL)-4 and up-regulation of interferon (IFN)-gamma responses by P. chabaudi-specific T cells and by reduction of P. chabaudi-specific immunoglobulin G1 (IgG1). The shift towards a Th1 cytokine pattern corresponded with efficient control of acute parasitaemia but an inability to resolve chronic infection. Moreover, combined CD80/CD86 blockade by using anti-CD80 and anti-CD86 monoclonal antibodies raised IFN-gamma production over that seen with CD86 blockade alone, with augmentation of this Th1-associated cytokine reducing levels of peak primary parasitaemia. These results demonstrate that IL-4 production by T cells in P. chabaudi-infected NIH mice is dependent upon CD86/CD28 interaction and that IL-4 and IFN-gamma contribute significantly, at different times of infection, to host resistance to blood stage malaria. In addition, combined CD80/CD86 blockade resulted in preferential expansion of IFN-gamma-producing T cells during P. chabaudi infection, suggesting that costimulatory pathways other than B7/CD28 may contribute to T-cell activation during continuous antigen stimulation. This study indicates a role for B7/CD28 costimulation in modulating the CD4+ T-cell response during malaria, and further suggests involvement of this pathway in other infectious and autoimmune diseases in which the Th cell immune response is also skewed.