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= CD1b = CD1b belongs to group 1 of CD1 family of transmembrane glycoproteins. CD1 molecules are expressed on the surface of numerous different human antigen presenting cells (DCs, monocytes and some thymocytes). This specialised group of glycoproteins present self and non-self lipid-based antigens to specific αβ T-cells. CD1 molecules are structurally related to major histocopatibility complex (MHC), they belongs to MHC class I-like genes. The human CD1 locus is lokalizate on chromosome 1 and contains five nonpolymorphic genes (CD1a, CD1b, CD1c, CD1d and CD1e).

Structure and function
CD1b molecules (as well as other CD1 and classical MHC I molecules) are formed by membrane-bound glycoprotein composed of three extracellular domains (α1,α2,α3). These extracellular domains are non-covalently associated with β2 microglobulin (which has the function of stabilising protein). This organization forms a narrow hydrophobic binding groove that accommodates lipid-based antigens. Binding groove is made up of four broadly interconnected pockets that are occupied by the alkyl chains of glycolipid and two detergent molecules. Compared to others CD1 molecules this unique arrangement of CD1b provides a possibility to bind a wide spectrum of antigens with various lenght of alkyl chains. Alkyl components of antigens are attached in hydrophobic groove and a hydrophilic part stands out from CD1b molecule and thus provides to the TCR a place to bind.

CD1b molecule has the largest antigen binding cleft within the CD1 family. Whereas the microbial lipids tend to have longer alkyl chains than self endogeneous lipids it seems that CD1b is specifically adapted to present microbial lipids (rather than endogeneous) to T cells.

Diseases
In case when immune system doesn't distinguish self and non-self structures it leads to autoreactive T-cell response. Autoreactive CD1b can recognize for example phospatidylglycerol, which is common for mammalian mitochodria and also bacteria. This autoantigen is released during a bacterial infection or mitochondrial stress. CD1b also presents endogenous gangliosides to specific T cells so they can commence autoimmune diseases such as multiple sclerosis.

Because CD1 molecules in contrast with major histocompatibility complex have restricted diversity, it could be an interesting marker for imunotherapy and target for development of new drugs.

Literature
MURPHY, Kenneth a Casey WEAVER. Janeway's immunobiology. 9th edition. New York, NY: Garland Science/Taylor & Francis Group, [2016]. ISBN 978-0-8153-4551-0