DC-SIGN (Dendritic Cell-Specific Intercellular adhesion molecule-3-Grabbing Non-integrin) also known as CD209 ( Cluster of Differentiation 209) is a

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, res ...

which in humans is encoded by the ''CD209'' gene. DC-SIGN is a

C-type lectin A C-type lectin (CLEC) is a type of carbohydrate-binding protein known as a lectin. The C-type designation is from their requirement for calcium for binding. Proteins that contain C-type lectin domains have a diverse range of functions including c ...

receptor present on the surface of both

macrophages Macrophages (abbreviated as M φ, MΦ or MP) ( el, large eaters, from Greek ''μακρός'' (') = large, ''φαγεῖν'' (') = to eat) are a type of white blood cell of the immune system that engulfs and digests pathogens, such as cancer ce ...

and

dendritic cells Dendritic cells (DCs) are antigen-presenting cells (also known as ''accessory cells'') of the mammalian immune system. Their main function is to process antigen material and present it on the cell surface to the T cells of the immune system. The ...

. DC-SIGN on macrophages recognises and binds with high affinity to high-mannose type N-glycans, a class of PAMPs (pathogen associated molecular patterns) commonly found on viruses, bacteria and fungi. This binding interaction activates

phagocytosis Phagocytosis () is the process by which a cell uses its plasma membrane to engulf a large particle (≥ 0.5 μm), giving rise to an internal compartment called the phagosome. It is one type of endocytosis. A cell that performs phagocytosis is ...

. On myeloid and pre-plasmacytoid

dendritic cell Dendritic cells (DCs) are antigen-presenting cells (also known as ''accessory cells'') of the mammalian immune system. Their main function is to process antigen material and present it on the cell surface to the T cells of the immune system. Th ...

s DC-SIGN mediates dendritic cell rolling interactions with blood

endothelium The endothelium is a single layer of squamous endothelial cells that line the interior surface of blood vessels and lymphatic vessels. The endothelium forms an interface between circulating blood or lymph in the lumen and the rest of the ve ...

and activation of

CD4 In molecular biology, CD4 (cluster of differentiation 4) is a glycoprotein that serves as a co-receptor for the T-cell receptor (TCR). CD4 is found on the surface of immune cells such as T helper cells, monocytes, macrophages, and dendritic ce ...

T cell A T cell is a type of lymphocyte. T cells are one of the important white blood cells of the immune system and play a central role in the adaptive immune response. T cells can be distinguished from other lymphocytes by the presence of a T-cell r ...

s, as well as recognition of

pathogen In biology, a pathogen ( el, πάθος, "suffering", "passion" and , "producer of") in the oldest and broadest sense, is any organism or agent that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a g ...

haptens.

Function

DC-SIGN is a C-type lectin and has a high affinity for the ICAM3 molecule. It binds various microorganisms by recognizing high-

mannose Mannose is a sugar monomer of the aldohexose series of carbohydrates. It is a C-2 epimer of glucose. Mannose is important in human metabolism, especially in the glycosylation of certain proteins. Several congenital disorders of glycosylat ...

-containing

glycoprotein Glycoproteins are proteins which contain oligosaccharide chains covalently attached to amino acid side-chains. The carbohydrate is attached to the protein in a cotranslational or posttranslational modification. This process is known as glyco ...

s on their surface, and can function as a co-receptor for several viruses such as HIV and

Hepatitis C Hepatitis C is an infectious disease caused by the hepatitis C virus (HCV) that primarily affects the liver; it is a type of viral hepatitis. During the initial infection people often have mild or no symptoms. Occasionally a fever, dark urine, ...

. Binding to DC-SIGN can promote HIV and Hepatitis C virus to infect target cells (T-cells and hepatocytes, respectively). Besides functioning as an

adhesion Adhesion is the tendency of dissimilar particles or surfaces to cling to one another ( cohesion refers to the tendency of similar or identical particles/surfaces to cling to one another). The forces that cause adhesion and cohesion can ...

molecule, recent studies have also shown that DC-SIGN can initiate innate immunity by modulating

toll-like receptor Toll-like receptors (TLRs) are a class of proteins that play a key role in the innate immune system. They are single-pass membrane-spanning receptors usually expressed on sentinel cells such as macrophages and dendritic cells, that recognize ...

s, though the detailed mechanism is not yet known. DC-SIGN together with other C-type lectins is involved in recognition of tumors by dendritic cells. DC-SIGN is also a potential engineering target for dendritic cell based cancer vaccine.

Role in HIV infection

This

molecule A molecule is a group of two or more atoms held together by attractive forces known as chemical bonds; depending on context, the term may or may not include ions which satisfy this criterion. In quantum physics, organic chemistry, and b ...

is involved in the initial stages of the

human immunodeficiency virus The human immunodeficiency viruses (HIV) are two species of ''Lentivirus'' (a subgroup of retrovirus) that infect humans. Over time, they cause acquired immunodeficiency syndrome (AIDS), a condition in which progressive failure of the immun ...

infection, as the HIV

gp120 Envelope glycoprotein GP120 (or gp120) is a glycoprotein exposed on the surface of the HIV envelope. It was discovered by Professors Tun-Hou Lee and Myron "Max" Essex of the Harvard School of Public Health in 1988. The 120 in its name comes from ...

molecule causes co-internalization of the DC-SIGN molecule and HIV virus particle (virion). The dendritic cell then migrates to the cognate lymphoid organ, whereupon recycling of the DC-SIGN/HIV virion complex to the cell periphery facilitates HIV infection of CD4⁺ T cells by interaction between DC-SIGN and ICAM-3.

Role in Ebola Virus infection/inhibition

Different studies have demonstrated that the ebola virus infection process starts when the virus reaches the cellular DC-SIGN receptor to infect the dendritic cells (of the immune system). In 2015 European researchers designed a “giant” molecule formed by thirteen fullerenes covered by carbohydrates which, by blocking DC-SIGN receptor, are able to inhibit the cell infection by an artificial ebola virus model. These antiviral molecules decorated with specific carbohydrates (sugars) present affinity by the receptor used as an entry point to infect the cell and act blocking it, thus inhibiting the infection in a sub-nanomolar range.

Gene family

DC-SIGN/CD209 is an animal "C-lectin", a large and diverse family of proteins found in both

prokaryote A prokaryote () is a single-celled organism that lacks a nucleus and other membrane-bound organelles. The word ''prokaryote'' comes from the Greek πρό (, 'before') and κάρυον (, 'nut' or 'kernel').Campbell, N. "Biology:Concepts & Con ...

s and

eukaryote Eukaryotes () are organisms whose cells have a nucleus. All animals, plants, fungi, and many unicellular organisms, are Eukaryotes. They belong to the group of organisms Eukaryota or Eukarya, which is one of the three domains of life. Bacter ...

s most of which are functional

lectins Lectins are carbohydrate-binding proteins that are highly specific for sugar groups that are part of other molecules, so cause agglutination of particular cells or precipitation of glycoconjugates and polysaccharides. Lectins have a role in rec ...

, meaning they bind carbohydrate

ligands In coordination chemistry, a ligand is an ion or molecule (functional group) that binds to a central metal atom to form a coordination complex. The bonding with the metal generally involves formal donation of one or more of the ligand's electr ...

, and whose ligand-binding affinity requires calcium (hence "C-lectin"). Among the animal C-lectins, a subfamily known as the ASGR ( asialoglycoprotein receptors) group contains several sub-sub-families, many of which are important to

innate immunity The innate, or nonspecific, immune system is one of the two main immunity strategies (the other being the adaptive immune system) in vertebrates. The innate immune system is an older evolutionary defense strategy, relatively speaking, and is the ...

. A cluster of genes in both humans and mice contains three related members of the "DC Receptor" class, so named because of their homology to DC-SIGN. Of these,

CD23 CD23, also known as Fc epsilon RII, or FcεRII, is the "low-affinity" receptor for IgE, an antibody isotype involved in allergy and resistance to parasites, and is important in regulation of IgE levels. Unlike many of the antibody receptors, CD23 ...

is, however, not expressed on dendritic cells but is a characteristic surface molecule of

B lymphocyte B cells, also known as B lymphocytes, are a type of white blood cell of the lymphocyte subtype. They function in the humoral immunity component of the adaptive immune system. B cells produce antibody molecules which may be either secreted or ...

s, and LSectin (CLEC4G) is expressed on the sinusoidal endothelium of the liver. The third gene group consists of multiple

paralogues Sequence homology is the biological homology between DNA, RNA, or protein sequences, defined in terms of shared ancestry in the evolutionary history of life. Two segments of DNA can have shared ancestry because of three phenomena: either a spec ...

of CD209. Thus, both primates and mice have multiple paralogues of CD209 more closely related to each other within the species than to their orthologous counterparts in the other species. Higher primates have at least three DC-SIGN genes, DC-SIGN, DC-SIGNL1 and DC-SIGNL2, although not all three are present in every species; DC-SIGNL2 has not been detected in humans. Eight paralogous of DC-SIGN have been reported in the laboratory mouse strain C57BL/6; these go by the names DC-SIGN, DC-SIGNR2...DC-SIGNR8. DC-SIGNR6 is a pseudogene. The genes labeled "DC-SIGN" in the human and mouse are thus not unique orthologues, although they resemble each other functionally and by being expressed on dendritic cells. Other members of the mouse CD209 gene group are differentially expressed on different cell types. For example, DC-SIGNR1 is expressed largely on macrophages in the marginal zones of the spleen and in the medulla of lymph nodes.

References

External links