Original Paper

Immunogenetics

, Volume 59, Issue 1, pp 77-91

Channel catfish leukocyte immune-type receptors contain a putative MHC class I binding site

  • James L. StaffordAffiliated withDepartment of Microbiology, University of Mississippi Medical Center
  • , Eva BengténAffiliated withDepartment of Microbiology, University of Mississippi Medical Center
  • , Louis Du PasquierAffiliated withInstitute of Zoology and Evolutionary Biology, University of Basel
  • , Norman W. MillerAffiliated withDepartment of Microbiology, University of Mississippi Medical Center
  • , Melanie WilsonAffiliated withDepartment of Microbiology, University of Mississippi Medical Center Email author 

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Abstract

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.

Keywords

Leukocyte receptor complex (LRC) Immunoglobulin superfamily (IgSF) MHC class I Leukocyte Ig-like receptors (LILRs) Teleosts Evolution