DC-Sign (dendritic cell specific intracellular adhesion molecule-grabbing nonintegrin; CD209) is a receptor primarily expressed by dendritic cells (DCs). Invading pathogens are defeated by immune cells of the innate and adaptive immune systems. The invaders are recognized by pattern recognition receptors, like TLRs and C-type lectin receptors. C-type lectins recognize carbohydrate structures on e.g. viruses and bacteria. This leads to the expression of specific cytokine which induce an adaptive Th immune response. A key C-type lectin expressed on DCs is DC-Sign. DC-Sign captures and internalizes antigen for presentation to T cells. After capturing of a pathogen via DC-Sign this leads to maturation of the DC resulting in migration from the peripheral tissue to the draining lymph node. To mediate its function in DC migration, DC-Sign is also a receptor for the recognition of self-glycoproteins, such as ICAM-3/2 as expressed by T-cells or endothelium. DC-Sign is a prototype II transmembrane receptor. DC-Sign recognizes many viruses via viral envelope glycoproteins. In some cases the virus uses this interaction to evade initiation of an adequate immune response, as known for HIV-1 infections. DC-Sign was originally discovered as HIV gp120 receptor in placenta. DC-Sign is expressed by immature DCs in peripheral tissue and mature DCs in lymphoid tissues and expression is regulated by IL-4. Besides DCs it is expressed on M2 macrophages, but not plasmacytoid DC and Langerhans cells. DC-Sign has in important role in the primary function of DCs, that is superior antigen-presenting capacity. Gene expression of DC-Sign is subjected to complex alternative splicing leading to several membrane-associated as well as soluble DC-Sign isoforms. There is little known about the expression and contribution in function of these isoforms. sDC-Sign can be found in blood, joint fluid and BAL. Expression of sDC-Sign is enhanced after CMV infection and seems to be regulated by IFN-γ and CXCL8/IL8. Although its precise function is unknown, it seems that the concentration of sDC-Sign is going down after virus infection or in cancer patients in comparison to healthy controls.