CD1b

CD1b is a group 1 CD1 antigen-presenting molecule that displays self and microbial lipid antigens to αβ and γδ T cells, thereby extending immune surveillance beyond peptide-based antigen recognition systems^[1][2]. Mechanistically, CD1b contains the largest antigen-binding groove within the CD1 family, including interconnected A′, C′, F′, and T′ pockets that accommodate lipids with long alkyl chains and support presentation of structurally diverse mycobacterial and endogenous lipids^[3][4]. Following intracellular trafficking through endosomal and lysosomal compartments, CD1b loads lipid antigens and forms complexes that activate CD1b-restricted T-cell responses^[5][6]. In disease-relevant settings, CD1b participates in immune recognition of microbial lipids, particularly those derived from Mycobacterium tuberculosis, and also presents self phospholipids and gangliosides that have been linked to autoreactive T-cell responses^[3][4]. Compared with related isoforms, CD1a and CD1c more closely reflect the overall cellular lipidome, whereas CD1b shows preferential association with sphingolipids and possesses a substantially larger antigen-binding cleft that enables presentation of longer lipid antigens^[3][4]. This structural specialization distinguishes CD1b from CD1a, CD1c, and CD1d and supports its role in studying lipid antigen presentation, host-pathogen interactions, and CD1-restricted T-cell biology^[1][3][6].