| Summary: | 碩士 === 國立清華大學 === 分子與細胞生物研究所 === 100 === 因申請專利緣故，資料延後公開Novel immune type receptors (NITRs) are a family of Ig like receptors found in zebrafish and other bony fish species. The NITRs resemble the human killer-cell immunoglobulin-like receptors (KIRs) both functionally and structurally. Both receptor families contain Ig like structures on their extracellular domain and ITIM-containing cytoplasmic tail or positively charged transmembrane domain in inhibiting or activating receptors, respectively. NITR9 is the only known activating member of the NITRs found in zebrafish thus far, but its physiological ligand was unknown. In this study, we showed that the binding of NITR9-Fc probe increased in zebrafish kidney and spleen cell populations post-infection along with increased zMHC class I mRNA and protein expression in zebrafish tissue homogenates. These findings in conjunction with the known HLA-KIR relationships prompted us to test whether zMHC class I served as the ligands for NITR9. This interaction was revealed by the direct association of NITR9-hFc with three zMHC class I UFA, UXA2 and UDA-L over-expressed in HEK293 cells in immunoprecipitation experiments. Structure-based modeling and alignment using HLA-A2*2402 as a template identified a FKNNIXXA motif shared by the 3 NITR9- associating zMHC class I, but not by the non-associating zMHC class I UDA. This motif is situated in close proximity with the HLA-Cw4-KIR2DL1contact site, suggesting its evolutionary conservation. The functional significance of zMHC class I-NITR9 interaction was indicated by the binding of purified recombinant UXA2 to NITR9/DAP10 or /DAP12 co-transfected HEK293 cells, but this binding may not be sufficient to initiate signaling in the autologous NITR9/DAP12 co-transfected zebrafish liver epithelial cells ZLE, suggesting insufficient avidity. UXA2-NITR9 association is the first identified zebrafish immune ligand-receptor system, which may play an important role in zebrafish immune defense against infection, a strategy probably conserved throughout the evolution of vertebrate immune system.
|
|---|
