Channel catfish leukocyte immune-type receptors contain a putative MHC class I binding site.
The recent identification of a large and diverse family of leukocyte immune-type receptors (IpLITRs) in channel catfish (Ictalurus punctatus) indicates that immunoglobulin superfamily (IgSF) members related to both mammalian Fc receptors (FcRs) and leukocyte receptor complex (LRC)-encoded proteins exist in fish. In the present study, it was found that IpLITR messages were preferentially up regulated in catfish peripheral blood leukocytes (PBL) and clonal cytotoxic T cells (CTL) after alloantigen stimulation. Detailed sequence analyses of the expressed IpLITR cDNAs from two clonal CTL lines indicated an unexpectedly large array of putative activatory and inhibitory IpLITR-types containing variable numbers of extracellular immunoglobulin (Ig)-like domains. Importantly, all expressed IpLITRs shared similar membrane distal Ig domains (i.e., D1 and D2), suggesting that they may bind a common type of ligand. Sequence alignments and comparative homology modeling revealed that IpLITR domains, D1 and D2, have similar predicted 3-D structural properties with the corresponding domains of the human LRC-encoded leukocyte Ig-like receptor (LILR) family. Furthermore, conservation of key major histocompatibility class I (MHC I)-binding residues were located at similar positions within the membrane distal tip of D1 between representative IpLITRs and group 1 LILRs. Taken together, these results suggest that fish LITRs have an orthologous relationship to LRC-encoded receptors such as the human LILRs and could potentially function as a diverse family of MHC class I-binding receptors.
Stafford
James L
JL
Department of Microbiology, University of Mississippi Medical Center, 2500 North State Street, Jackson, MS, 39216-4505, USA.
Bengtén
Eva
E
Du Pasquier
Louis
L
Miller
Norman W
NW
Wilson
Melanie
M
D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D015395:Histocompatibility Antigens Class I / Q000276:immunology*; D007059:Ictaluridae / Q000235:genetics / Q000276:immunology*; D007962:Leukocytes / Q000187:drug effects / Q000276:immunology; D008024:Ligands; D008969:Molecular Sequence Data; D011487:Protein Conformation; D011971:Receptors, Immunologic / Q000737:chemistry / Q000235:genetics / Q000276:immunology*
D015395:Histocompatibility Antigens Class I; D008024:Ligands; D011971:Receptors, Immunologic