Porcine aortic endothelial cells transfected with HLA-G are partially protected from xenogeneic human NK cytotoxicity

In this study we tested whether the expression of HLA-G protects porcine en dothelial cells (PEC) from the lysis mediated by human natural killer (NK) cells. Because HLA-E is nor: present in PEG, this model provides an ideal t ool to study the direct role of HLA-G in NK inhibition. Immortalized porcin e aortic endothelial cells (PED) were stably transfected with a vector codi ng for the HLA-G1 protein and surface expression was demonstrated by Row cy tometry analysis. Although the adhesion of human NK cells to FED was not co mpromised by HLA-G, the expression of HLA-G partially protected FED from th e lysis mediated by polyclonal NK lines derived from different donors. A de crease of the surface-expression of HLA-G on FED corresponded to a loss of the capacity of FED to inhibit NK cytotoxicity, indicating chat the surface density of HLA-G molecules must exceed a certain threshold to protect targ et cells. In summary, these data show that HLA-G, independent from the pres ence of HLA-E, can only partially and inefficiently protect FED from human NE; cell-mediated cytotoxicity. Because ILT-2/LIR-1 expression did not corr elate with HLA-G mediated inhibit ion, we hypothesize that other yet uniden tified receptors expressed by peripheral blood NK cells are involved in the recognition of HLA-G. (C) American Society for Histocompatibility and Immu nogenetics, 2000. Published by Elsevier Science Inc.