, Volume 59, Issue 1, pp 77-91
Date: 06 Dec 2006

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

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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.

GenBank Submissions: The sequences presented in this article have been submitted to GenBank under the following accession numbers: TS32.15 L1.1a (DQ858227); TS32.15 L1.1b (DQ858228); TS32.15 L1.1c (DQ858229); TS32.15 L1.2a1 (DQ858230); TS32.15 L1.2a2 (DQ858231); TS32.15 L1.2a3 (DQ858232); TS32.15 L1.2a4 (DQ858233); TS32.15 L1.2b1 (DQ858234); TS32.15 L1.2b2 (DQ858235); TS32.15 L1.2b3 (DQ858236); TS32.15 L1.2c1 (DQ858237); TS32.15 L1.2c2 (DQ858238); TS32.15 L1.2c3 (DQ858239); TS32.17 L1.1a (DQ858240); TS32.17 L1.1b (DQ858241); TS32.17 L1.2a (DQ858242); TS32.17 L1.2b (DQ858243); TS32.15 L2.1a (DQ860158); TS32.15 L2.2a (DQ860159); TS32.15 L2.2b (DQ860160); TS32.15 L2.2c (DQ860161); TS32.15 L2.3a (DQ860162); TS32.15 L2.3b (DQ860163); TS32.15 L2.3c (DQ860164); TS32.15 L2.4a (DQ860165); TS32.15 L2.4b (DQ860166); TS32.15 L2.4c (DQ860167); TS32.15 L2.5a (DQ860168); TS32.15 L2.5b (DQ860169); TS32.15 L2.6a (DQ860170); TS32.15 L2.6b (DQ860171); TS32.17 L2.1a (DQ860172); TS32.17 L2.1b (DQ860173); TS32.17 L2.2a (DQ860174); TS32.17 L2.2b (DQ860175); TS32.17 L2.3a (DQ860176); TS32.17 L2.3b (DQ860177).