DC-SIGN1 is a type II protein C-type lectin that binds mannose-rich molecules such as ICAM-3 and ICAM-2 in a calcium dependent manner. DC-SIGN1, a 44kDa molecule, is identical to the HIV-1 binding protein. Analysis of various tissues and cell lines suggests that DC-SIGN1 expression is restricted to dendritic cells, although there is evidence of expression in placenta, resting monocytes, and monocytic cell lines. DC-SIGN2 (DC-SIGNR), located on human chromosome 19p13.3, shares 73-80% amino acid identity with DC-SIGN1. DC-SIGN2 is polymorphic and is primarily transcribed in the liver and lymph nodes but not in monocyte-derived DC. Expression of DC-SIGN2 is restricted to endothelial cells derived from liver sinusoids, lymph nodes sinuses, and capillaries. Membrane and soluble forms of the protein have also been found to be expressed in placenta and some monocytic cell lines.
DC-SIGN1 is involved in molecular interactions between dendritic cells and resting T-cells. DC-SIGN interacts with viruses such as X4, R5, X4R5 HIV-1 strains, HIV-2, and SIV. It captures HIV-1 through its interaction with the gp120 envelope glycoprotein and promotes efficient infection of CD4+ T cells that co-express chemokine receptors. DC-SIGN2 also binds mannose residues in a calcium dependent fashion, including ICAM-3 and HIV-1 gp120. It binds to human and simian immunodeficiency viruses and activates infection in trans.
