Molecular Genetic Analysis of Class Ib MHC-related Genes : Identification of Rat Homologues of Tla and CD1 Genes.

The class Ib antigens are a group of molecules structurally related to classical class I molecules (H-2K, -D, HLA-A, -B, -C) non-covalently associated with β2-microglobulim. The function of class Ib is still uncertain. No class Ib homologous genes have been extensively investigated besides mice and humans. If these class Ib molecules have an indispensable integrated function, they would be conserved in evolution. We investigated the conservation of two class Ib molecules, TL and CD1 antigens, which had been thought to be homologous products. The following results were obtained. (1) Tla genes are conserved in mouse-like rodents (mouse, rat and hamster), but not in other mammals (human, rabbit, guinea-pig and mongolian-gerbil). (2) A partial DNA sequence of the rat Tla homologues have a high DNA similarity to mouse T18dgene encoding TL antigen. (3) Transcription of rat Tla genes has not been detected. (4) At least two CD1 genes have been found in rat and expressed in thymus. These results imply a possible functional complementation between TL and CD1