CD1D

CD1D is the is_associated_with::human is_associated_with::gene that encodes the is_associated_with::protein CD1d, a member of the is_associated_with::CD1 (cluster of differentiation 1) family of is_associated_with::glycoproteins expressed on the surface of various human is_associated_with::antigen-presenting cells. They are non-classical MHC proteins, related to the is_associated_with::class I MHC proteins, and are involved in the presentation of lipid is_associated_with::antigens to is_associated_with::T cells. CD1d is the only member of the group 2 CD1 molecules.

Biological significance
CD1d-presented lipid antigens activate a special class of T cells, known as natural killer T (NKT) cells, through the interaction with the is_associated_with::T-cell receptor present on NKT membranes. When activated, NKT cells rapidly produce Th1 and is_associated_with::Th2 is_associated_with::cytokines, typically represented by is_associated_with::interferon-gamma and is_associated_with::interleukin 4 production.

Nomenclature
CD1d is also known as R3G1

Ligands
Some of the known ligands for CD1d are:
 * α-is_associated_with::galactosylceramide (α-GalCer), a compound originally derived from the marine sponge is_associated_with::Agelas mauritanius with no physiological role but great research utility.
 * α-glucuronyl- and α-galacturonyl- is_associated_with::ceramides, a family of compounds of microbial origin which can be found, for example, on the is_associated_with::cell wall of is_associated_with::Sphingomonas, a ubiquitous is_associated_with::Gram-negative is_associated_with::bacterium. The related β-D-glucopyranosylceramide is accumulated in is_associated_with::antigen-presenting cells after infection, where it serves to activate is_associated_with::invariant NKTs (iNKTs), a special kind of NKT.
 * is_associated_with::iGb3, a self antigen which has been implied in iNKT selection.
 * HS44, a synthetic amino is_associated_with::cyclitolic ceramide analogue which has less contact with the TCR, activating iNKTs in a more constrained way than α-GalCer (specially in relation to Th2 cytokines production) and thus being more interesting for therapeutic use.

CD1d tetramers
CD1d is_associated_with::tetramers are protein constructs composed of four CD1d molecules joined together and usually fluorescently labelled, used to identify NKT cells or other CD1d-reactive cells. In particular, type I NKT cells and some type II NKT cells are stained by them. A differentiation of these two types can be obtained in human by using an antibody against the TCR Vα24 chain, which is specific of type I NKT cells.

Although they are the most widely used of CD1d oligomers, sometimes CD1d dimers (two units) or pentamers (five units) are used instead.