Type I IFNs differentially modulate IL-12p70 production by human dendritic cells depending on the maturation status of the cells and counteract IFN-gamma-mediated signaling.

Type I IFNs (IFNalpha/beta) are approved for the treatment of a variety of diseases, including the autoimmune disease multiple sclerosis (MS). The proinflammatory cytokines IL-12 and IFN-gamma have been proposed to contribute to the pathogenesis of MS. Since dendritic cells (DCs) are recognized as major producers of IL-12p70 and promote the development of IFN-gamma-producing Th1 cells, we investigated the direct effect of IFNalpha/beta on monocyte-derived DCs at different stages of development. We demonstrate that IFNalpha/beta enhance IL-12p70 production by immature DCs but inhibit IL-12p70 production by mature DCs. Importantly, IFNalpha/beta strongly counteracted the IL-12-enhancing effect of IFN-gamma on DCs irrespective of their maturation status. Exposure of DCs to IFNalpha/beta during maturation does not affect their maturation or cytokine profile upon CD40 ligation. The differential modulatory effect of IFNalpha/beta on the IL-12-producing capacity of DCs and their cross-regulatory effect on IFN-gamma may reduce inflammatory processes and therefore be therapeutically effective in MS.

IgE production after antigen-specific and cognate activation of HLA-DPw4-restricted T-cell clones, by 78% of randomly selected B-cell donors.

The frequency of expression of the MHC class II antigen, HLA-DPw4, in the caucasoid population is approximately 78%, and is unmatched by phenotypic frequencies of other HLA class II molecules. Here we describe three human Der-P1-specific T-cell clones (TCC), restricted by the HLA-DPw4-variant HLA-DPB1*0401, of which two TCC also responded to antigen, presented on HLA-DPB1*0402. Thus, randomly selected caucasoid donors present a 78% chance for a correct match with these HLA-DPw4-restricted TCC. This allows comparative in vitro antigen presentation studies with various antigen presenting cells (APC) from different (healthy or diseased) donors without the variable influence of responding T cells. It was subsequently demonstrated that the TCC can be used to study antigen-induced IgE production in randomly selected primary B cells. Cognate HLA-DPw4-restricted antigen presentation caused enhanced immunoglobulin production of IgE, IgG1, IgA and IgM, of which only IgE induction was reversed by addition of anti-IL-4 antibodies.

Granulocyte-macrophage colony-stimulating factor (GM-CSF) has opposing effects on the capacity of monocytes versus monocyte-derived dendritic cells to stimulate the antigen-specific proliferation of a human T cell clone.

GM-CSF is widely used in combination with IL-4 to differentiate monocytes into potent T cell stimulatory cells, referred to as monocyte-derived dendritic cells (MoDC). These cytokines further increased the stimulatory function of MoDC when present during their incubation with antigen, as determined by the proliferative response of an allergen-specific T cell clone. Conversely, the incubation of freshly isolated monocytes with antigen in the presence of GM-CSF or GM-CSF and IL-4 strongly inhibited the specific stimulation of the T cells, compared with monocytes pulsed in the absence of cytokines. This suppression was partly due to the secretion of prostaglandin E2 (PGE2) and IL-10 by GM-CSF-treated monocytes, since the combined use of indomethacin and anti-IL-10 antibodies during GM-CSF incubation and antigen pulsing restored T cell growth to about 65% of control levels. As confirmed by culture supernatant transfer experiments, maximal inhibition of T cell stimulation was also dependent on the direct contact between the T cells and GM-CSF-treated monocytes during antigen presentation. Collectively, these results imply that GM-CSF can either inhibit or enhance the re-stimulation of primed T cells by antigen-presenting monocytes or MoDC, respectively.