Modulation of the immune and inflammatory responses by Plasmodium falciparum schizont extracts: role of myeloid dendritic cells in effector and regulatory functions of CD4+ lymphocytes.

The optimal immune response to malaria infection comprises rapid induction of inflammatory responses promptly counteracted by regulatory mechanisms to prevent immunopathology. To evaluate the role of dendritic cells (DC) in the balance of parasite-induced inflammatory/anti-inflammatory mechanisms, we studied the activity of monocyte-derived dendritic cells (MDDC), previously exposed to soluble extracts of Plasmodium falciparum-infected red blood cells (PfSE), in the differentiation of CD4 cells isolated from donors never exposed to malaria infection. We show that MDDC exposed to PfSE are extremely efficient to induce a contemporary differentiation of TH1 effector cells and T regulatory (Treg) cells in CD4 T cells even when exposed to low concentrations of parasitic extracts. Treg cells induced by MDDC infected with PfSE (MDDC-PfSE) produce transforming growth factor beta (TGF-ß) and interleukin 10 (IL-10) and are endowed with strong suppressive properties. They also show phenotypical and functional peculiarities, such as the contemporary expression of markers of Treg and TH1 differentiation and higher sensitivity to TLR4 ligands both inducing an increasing production of suppressive cytokines. On the whole, our data indicate that MDDC exposed to PfSE orchestrate a well-balanced immune response with timely differentiation of TH1 and Treg cells in CD4 cells from nonimmune donors and suggest that, during the infection, the role of MDCC could be particularly relevant in low-parasitemia conditions.

Plasmodium falciparum soluble extracts potentiate the suppressive function of polyclonal T regulatory cells through activation of TGFß-mediated signals.

Increased numbers of T regulatory cells (Tregs), key mediators of immune homeostasis, were reported in human and murine malaria and it is current opinion that these cells play a role in balancing protective immunity and pathogenesis during infection. However, the mechanisms governing their expansion during malaria infection are not completely defined. In this article we show that soluble extracts of Plasmodium falciparum (PfSEs), but not equivalent preparation of uninfected erythrocytes, induce the differentiation of polyclonally activated CD4(+) cells in Tregs endowed with strong suppressive activity. PfSEs activate latent TGFß bound on the membrane of Treg cells, thus allowing the cytokine interaction with TGFß receptor, and inducing Foxp3 gene expression and TGFß production. The activation of membrane-bound latent TGFß by PfSEs is significantly reduced by a broad-spectrum metalloproteinases inhibitor with Zn(++) -chelating activity, and completely inhibited by the combined action of such inhibitor and antibodies to a P. falciparum thrombospondin-related adhesive protein (PfTRAP). We conclude that Pf-Zn(++) -dependent proteinases and, to a lesser extent, PfTRAP molecules are involved in the activation of latent TGFß bound on the membrane of activated Treg cells and suggest that, in malaria infection, this mechanism could contribute to the expansion of Tregs with different antigen specificity.

Sex differences in the response to viral infections: TLR8 and TLR9 ligand stimulation induce higher IL10 production in males.

BACKGROUND: Susceptibility to viral infections as well as their severity are higher in men than in women. Heightened antiviral responses typical of women are effective for rapid virus clearance, but if excessively high or prolonged, can result in chronic/inflammatory pathologies. We investigated whether this variability could be in part attributable to differences in the response to the Toll-Like Receptors (TLR) more involved in the virus recognition. METHODS: Cytokine production by peripheral blood mononuclear cells (PBMCs) from male and female healthy donors after stimulation with Toll-like receptors (TLR) 3, 7, 8, 9 ligands or with viruses (influenza and Herpes-simplex-1) was evaluated. RESULTS: Compared to females, PBMCs from males produced not only lower amounts of IFN-α in response to TLR7 ligands but also higher amounts of the immunosuppressive cytokine IL10 after stimulation with TLR8 and TLR9 ligands or viruses. IL10 production after TLR9 ligands or HSV-1 stimulation was significantly related with plasma levels of sex hormones in both groups, whereas no correlation was found in cytokines produced following TLR7 and TLR8 stimulation. CONCLUSIONS: Given the role of an early production of IL10 by cells of innate immunity in modulating innate and adaptive immune response to viruses, we suggest that sex-related difference in its production following viral nucleic acid stimulation of TLRs may be involved in the sex-related variability in response to viral infections.