MHC class I genes of the channel catfish: sequence analysis and expression

Four cDNAs encoding the major histocompatibility complex (MHC) class I alph a chain were isolated from a channel catfish clonal B-cell cDNA library. Se quence analysis suggests these cDNAs represent three different MHC class I loci. All cDNAs encoded conserved residues characteristic of the MHC class I alpha chain: namely, those involved in peptide binding, salt bridges, dis ulfide bond formation, and glycosylation. Southern blot analyses of individ ual outbred and second-generation gynogenetic fish indicated the existence of both polygenic and polymorphic loci. Northern blot studies demonstrated that catfish B, T, and macrophage cell lines transcribed markedly higher le vels of class I cu and beta(2)-microglobulin (beta(2)m) mRNA than fibroblas t cell lines. In addition, immunoprecipitation data showed that a 41 000 M- r glycoprotein (presumably class I alpha) was associated with beta(2)m on t he surface of catfish B cells. This latter finding is the first direct evid ence for the cell surface association of beta(2)m with the MHC class I alph a chain on teleost cells and supports the notion that functional MHC class I proteins exist in teleosts.