Molecular cloning and characterization of a novel CD1 gene from the pig

Much effort is underway to define the immunological functions of the CD1 mu ltigene family; which encodes a separate lineage of Ag presentation molecul es capable of presenting lipid and glycolipid Ags, To identify porcine CD1 homologues, a cosmid library was constructed and screened with a degenerate CD1 alpha 3 domain probe. One porcine CD1 gene (pCD1.1) was isolated and f ully characterized, The pCD1.1 gene is organized similarly to MHC class I a nd other CD1 genes and contains an open reading frame of 1020 bp encoding 3 39 amino acids. Expression of pCD1.1 mRNA was observed in CD3(-) thymocytes , B lymphocytes, and tissue macrophages and dendritic cells. The pCD1.1 cDN A was transfected into Chinese hamster ovary cells, and subsequent FAGS ana lysis demonstrated that mAb 76-7-4, previously suggested to be a pig CD1 mA b, recognizes cell surface pCD1.1. Structurally, the pCD1.1 alpha 1 and alp ha 2 domains are relatively dissimilar to those of other: CD1 molecules, wh ereas the alpha 3 domain is conserved. Overall, pCD1.1 bears the highest si milarity with human CD1a, and the ectodomain sequences characteristically e ncode a hydrophobic Ag-binding pocket. Distinct from other CD1 molecules, p CD1.1 contains a putative serine phosphorylation moth similar to that found in human, pig, and mouse MHC class Ia molecules and to that found in roden t, but not human, MHC class-I related (MR1) cytoplasmic tail sequences. Thu s, pCD1.1 encodes a molecule with a conventional. CD1 ectodomain and an MHC class I-like cytoplasmic tail. The unique features of pCD1.1 provoke intri guing questions about the immunologic functions of CD1 and the evolution of Ag presentation gene families.