Properdin and factor H production by human dendritic cells modulates their T‐cell stimulatory capacity and is regulated by IFN‐γ

Dendritic cells (DCs) and complement are both key members of the innate and adaptive immune response. Recent experimental mouse models have shown that production of alternative pathway (AP) components by DCs strongly affects their ability to activate and regulate T‐cell responses. In this study we investigated the production and regulation of properdin (fP) and factor H (fH) both integral regulators of the AP, by DCs and tolerogenic DCs (tolDCs). Both fP and fH were produced by DCs, with significantly higher levels of both AP components produced by tolDCs. Upon activation with IFN‐γ both cells increased fH production, while simultaneously decreasing production of fP. IL‐27, a member of the IL‐12 family, increased fH, but production of fP remained unaffected. The functional capacity of fP and fH produced by DCs and tolDCs was confirmed by their ability to bind C3b. Inhibition of fH production by DCs resulted in a greater ability to induce allogenic CD4+ T‐cell proliferation. In contrast, inhibition of fP production led to a significantly reduced allostimulatory capacity. In summary, this study shows that production of fP and fH by DCs, differentially regulates their immunogenicity, and that the local cytokine environment can profoundly affect the production of fP and fH. Dendritic cells produce properdin and factor H, key opposing regulators of the alternative pathway of complement. IFN‐γ stimulation decreased DC derived properdin while simultaneously increasing factor H production. siRNA inhibition of DC derived properdin reduced T cell proliferation, while silencing DC factor H promoted T cell expansion and IFN‐γ production.