The sheep CD1 gene family contains at least four CD1B homologues

We identified four cDNA sequences encoding sheep homologues of the CD1 molecule. The sheep sequences were selected from lambdagt11 thymocyte cDNA libraries by hybridization with a human CD1C probe and a homologous sheep probe. The SCD1B-42 and SCD1A25 sequences encode complete CD1 molecules. The third sequence, SCD1B-52, which is closely related to SCD1B-42 and may be an allele, has the sequence encoding the alpha3 region precisely deleted. The fourth sequence, SCD1T10, is truncated at the 5' end. All four sequences are related to the human CD1B and domestic rabbit CD1B-like sequences at both nucleotide and amino acid level. Comparison of the derived CD1 amino acid sequences with the sequence of major histocompatibility complex class I molecules showed that the sheep CD1 molecules, like human CD1 molecules, lack most of the conserved class I residues known to be involved in interaction with beta2-microglobulin and the CD8 molecule. They do not contain the peptide docking residues involved in anchoring peptides in the peptide binding groove of class I molecules. Southern hybridization of sheep DNA with a sheep CD1 exon 4/alpha3 probe showed that the sheep genome encodes at least seven CD1 genes. The implications of these analyses for CD1 function are discussed.