Characterization of the Chicken C-Type Lectin-Like Receptors B-NK and B-lec Suggests That the NK Complex and the MHC Share a Common Ancestral Region

• Published in: The Journal of immunology (1950) 2005-03, Vol.174 (6), p.3475-3483
• Main Authors: Rogers, Sally L, Gobel, Thomas W, Viertlboeck, Birgit C, Milne, Sarah, Beck, Stephan, Kaufman, Jim
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Animals; Base Sequence; Chickens - genetics; Chickens - immunology; DNA, Complementary - genetics; Evolution, Molecular; Humans; Killer Cells, Natural - immunology; Lectins, C-Type - genetics; Lymphoid Tissue - immunology; Major Histocompatibility Complex; Models, Genetic; Models, Immunological; Molecular Sequence Data; Phylogeny; Receptors, Immunologic - genetics; Sequence Homology, Amino Acid
• ISSN: 0022-1767; 1550-6606
• DOI: 10.4049/jimmunol.174.6.3475

The sequencing of the chicken MHC led to the identification of two open reading frames, designated B-NK and B-lec, that were predicted to encode C-type lectin domains. C-type lectin domains are not encoded in the MHC of any animal described to date; therefore, this observation was completely unexpected, particularly given that the chicken has a "minimal essential MHC." In this study, we describe the initial characterization of the B-NK and B-lec genes, and show that they share greatest homology with C-type lectin-like receptors encoded in the human NK complex (NKC), in particular NKR-P1 and lectin-like transcript 1 (LLT1), respectively. In common with NKR-P1 and LLT1, B-NK and B-lec are located next to each other and transcribed in opposite orientation. Like human NKR-P1, B-NK has a functional inhibitory signaling motif in the cytoplasmic tail and is expressed in NK cells. In contrast, B-lec contains an endocytosis motif in the cytoplasmic tail, and like LLT1, is an early activation Ag. Further analysis leads us to propose that there are four subgroups of C-type lectin-like receptors in the NKC, which arose as a result of duplication events. Moreover, this analysis suggests that the NKC may be considered a fifth paralogous region, and therefore shares an ancient common origin with the MHC. This provides evidence that C-type lectin-like receptors were present in the preduplication, primordial MHC region, and suggests that an original function of MHC molecules was for recognition by NK cell receptors encoded nearby.