Evidence that gC1qR and DC-SIGN associate on the surface of immature dendritic cells (136.24)

Complement protein C1q is involved in many immunoregulatory functions, such as modulating T-cell proliferation and regulating dendritic cell (DC) differentiation and maturation. C1q has at least two multi-functional cell surface receptors, cC1qR and gC1qR. While these receptors ostensibly lack a direct conduit into intracellular elements, they are known to form docking/signaling complexes with transmembrane partners. DC-SIGN (dendritic cell-specific-ICAM-grabbing-non integrin) is a C-type lectin expressed on the surface of DCs and involved in T-cell activation and endocytosis. Because SIGN-R1, a C-type lectin related to DC-SIGN has been shown to bind directly to C1q, we investigated whether DC-SIGN also binds to C1q and if DC-SIGN may act as a transmembrane partner for gC1qR and/or cC1qR. Using flow cytometry, we found that DC-SIGN, gC1qR and cC1qR are all present on the surface of human immature DCs (iDC) grown in culture. While antigen-capture ELISA experiments using iDC lysates showed that C1q, gC1qR and cC1qR directly or indirectly associate with DC-SIGN, immunofluorescence microscopy revealed that C1q and gC1qR, but not cC1qR co-localize with DC-SIGN on the surface of iDCs. The data suggest that DC-SIGN and gC1qR may directly associate on the surface of iDCs and regulate DC differentiation in a stage specific manner. Since both gC1qR and DC-SIGN have been shown to bind HIV, it is possible that the two receptors may play a role in the pathogenesis of HIV-AIDS.