Alpha-gal-independent dual recognition and activation of xenogeneic endothelial cells and human naive natural killer cells

Background. Interaction between vascularized xenograft and host immune system is thought to occur via Galactose α (1,3) Galactose (Galα 1,3 gal) structures decorating the xenograft. Methods. We raised anti-Galα 1,3 gal-BSA polyclonal antibodies in baboons and investigated effect(s) of these antibodies as well as soluble Galα 1,3 gal-BSA on human naive natural killer (NK) cell interactions with porcine aortic endothelial cells. Results. We demonstrate that human naive (unstimulated) NK cells recognize xenogeneic endothelial cells under conditions where binding to the Galα 1,3 gal structures is minimized by the presence of blocking anti-Galα 1,3 gal IgG or soluble Galα 1-3 gal and in the absence of xenoreactive natural antibodies and complement. After xenogeneic encounter both endothelial cells and human NK cells are activated. Endothelial cell activation is rapid and is manifested initially by an intraendothelial calcium transient and subsequently by expression of P-selectin and vascular endothelial cell adhesion molecule-1 on the xenoendothelium surface. NK cell activation is manifested by increased expression of perforin and increased cytotoxicity towards the xenoendothelium. Neither recognition nor activation of the xenoendothelium was affected by the introduction of either anti-Galα 1,3 gal IgG or soluble Galα 1-3 gal. Conclusion. Our data provide evidence that innate immune cells, such as NK cells, recognize and activate xenoendothelial cells independently of Galα 1-3 gal structures and raise the possibility of novel interactive sites on both human naive NK cells and discordant xenogeneic endothelium.