The mouse monoclonal antibody 51.1 recognizes an extracellular epitope of CD1d, a 38 kDa transmembrane glycoprotein expressed mainly on cortical thymocytes, marginal zone B cells and other antigen presenting cells, but also i e.g. hepatitis C virus-infected livers.
CD1d molecule,CD1d belongs to CD1 family of transmembrane glycoproteins, associated with beta2 microglobulin, similarly to MHC I molecules. Unlike other CD1 family members, however, CD1d can be also expressed in a non-glycosylated form, which is not associated with beta2 microglobulin. Hence it is not certain how much CD1d plays a role in the presentation of microbial lipid antigens during infection. On the other hand, it is expressed on various antigen presenting cell types. Besides it, CD1d+ thymocytes are involved in the positive selection of sublineage of NKT cells.