HLA-E and HLA-G expression on porcine endothelial cells inhibit xenoreactive human NK cells through CD94/NKG2-dependent and -independent pathways.
Human NK cells contribute a significant role to host defense as well as xenogeneic cytotoxicity. Previous studies using human 721.221 cell line have shown that peptides derived from the leader sequence of the HLA-G binds and up-regulates the surface expression of HLA-E molecules, which was considered to consequently provide negative signals to human NK cells. However, the direct role of HLA-G in inhibiting human NK cells remains controversial. In this study, we showed that the expression of HLA-G or HLA-E in porcine endothelial cells directly protected sensitive porcine cells from human NK cell-mediated xenogeneic cytotoxicity. Ab blocking assays using F(ab')2 of the HLA class I-specific mAb PA2.6 indicated that the protection was directly mediated by the expression of HLA-G and HLA-E on the porcine cells. The HLA-E-mediated protection was blocked by anti-human CD94 Ab. In addition, the engagement of HLA-E lead to the phosphorylation of the CD94/NKG2 complex and the recruitment of SH2 domain-containing protein phosphatase 1 (SHP-1) to the complex. Therefore, HLA-E protected porcine cells from xenoreactive human NK cells through a CD94/NKG2-dependent pathway. In contrast, HLA-G inhibited human NK cells in the absence of CD94/NKG2 phosphorylation or SHP-1 recruitment, and the inhibition was not blocked by anti-CD94 Ab. Therefore, HLA-G protected porcine cells from human NK cells through a CD94/NKG2-independent pathway. These results demonstrated that both HLA-E and HLA-G could directly inhibit human NK cells in the absence of other endogenous HLA class I molecules. These results also have practical implications in preventing xenograft rejection mediated by human NK cells.
Sasaki
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Departments ofSurgery and Pathology, Washington University School of Medicine, St. Louis, MO 63110, USA.
Xu
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Mohanakumar
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D000818:Animals; D015478:Antigens, Heterophile / Q000276:immunology*; D001011:Aorta / Q000166:cytology / Q000276:immunology; D003601:Cytotoxicity Tests, Immunologic; D003602:Cytotoxicity, Immunologic; D004730:Endothelium, Vascular / Q000166:cytology / Q000276:immunology*; D006680:HLA Antigens / Q000235:genetics / Q000276:immunology*; D059951:HLA-G Antigens; D015395:Histocompatibility Antigens Class I / Q000235:genetics / Q000276:immunology*; D006801:Humans; D007694:Killer Cells, Natural / Q000276:immunology*; D011994:Recombinant Proteins / Q000276:immunology; D013552:Swine; D000097625:HLA-E Antigens
D015478:Antigens, Heterophile; D006680:HLA Antigens; D059951:HLA-G Antigens; D015395:Histocompatibility Antigens Class I; D011994:Recombinant Proteins; D000097625:HLA-E Antigens