Regulating the adaptive immune response to blood-stage malaria: role of dendritic cells and CD4⁺Foxp3⁺ regulatory T cells.

Although a clearer understanding of the underlying mechanisms involved in protection and immunopathology during blood-stage malaria has emerged, the mechanisms involved in regulating the adaptive immune response especially those required to maintain a balance between beneficial and deleterious responses remain unclear. Recent evidence suggests the importance of CD11c⁺ dendritic cells (DC) and CD4⁺Foxp3⁺ regulatory T cells in regulating immune responses during infection and autoimmune disease, but information concerning the contribution of these cells to regulating immunity to malaria is limited. Here, we review recent findings from our laboratory and others in experimental models of malaria in mice and in Plasmodium-infected humans on the roles of DC and natural regulatory T cells in regulating adaptive immunity to blood-stage malaria.

Dendritic cell and NK cell reciprocal cross talk promotes gamma interferon-dependent immunity to blood-stage Plasmodium chabaudi AS infection in mice.

Dendritic cells (DCs) are important accessory cells for promoting NK cell gamma interferon (IFN-gamma) production in vitro in response to Plasmodium falciparum-infected red blood cells (iRBC). We investigated the requirements for reciprocal activation of DCs and NK cells leading to Th1-type innate and adaptive immunity to P. chabaudi AS infection.

Interaction of mouse dendritic cells and malaria-infected erythrocytes: uptake, maturation, and antigen presentation.

Consistent with their seminal role in detecting infection, both mouse bone marrow-derived and splenic CD11c+ dendritic cells (DCs) exhibited higher levels of uptake of Plasmodium chabaudi-parasitized RBCs (pRBCs) than of noninfected RBCs (nRBCs) as determined by our newly developed flow cytometric technique using the dye CFSE to label RBCs before coculture with DCs. To confirm that expression of CFSE by CD11c+ cells following coculture with CFSE-labeled pRBCs represents internalization of pRBC by DCs, we showed colocalization of CFSE-labeled pRBCs and PE-labeled CD11c+ DCs by confocal fluorescence microscopy. Treatment of DCs with cytochalasin D significantly inhibited the uptake of pRBCs, demonstrating that uptake is an actin-dependent phagocytic process.

Interleukin-15 enhances innate and adaptive immune responses to blood-stage malaria infection in mice.

Compared to C57BL/6 wild-type mice, interleukin-15(-/-) (IL-15(-/-)) mice showed delayed clearance of Plasmodium chabaudi AS infection, lower type 1 cytokine production, impaired dendritic cell and NK cell functions, and lower titers of malaria-specific antibodies. Thus, IL-15 supports early control and timely resolution of blood-stage malaria through promotion of Th1-dependent innate and adaptive immune responses.