Nitric oxide production by pig endothelial cells in response to human-derived injury

Background. The hyperacute rejection induced by natural antibodies is the f irst; barrier to the success of pig to human organ xenotransplantation, Whe n this barrier is overcome, an infiltrate of mainly monocytes and natural k iller cells can be observed. Nitric oxide (NO) has been described to be inv olved in allo- and xenorejection, and to participate in tbe regulation of m onocyte infiltration in other models. Methods, We have studied the capacity of human monocytes and natural antibo dies to induce the production of NO by pig endothelial cells, by measuring NO2, a stable end product of NO. Results. Human monocytes can induce HuProVim (HUP), a pig endothelial line, and "in situ, ex vive" pig endothelial cells to produce NO2. This NO2 prod uction was inhibited by N-G-nitro-L-arginine-methylester and N-G-monomethyl -L-arginine, inhibitors of NO production. This induction can be observed ev en if cells are separated by a semipermeable membrane, which indicates that it is a result of soluble factors. Activated cells continue producing NO a fter triggering for 1 hr. No NO2 production was observed after activation o f HUP cells with recombinant human interleukin (IL)-1 alpha, IL-1 beta, IL- 6, IL-10, transforming growth factor-beta 1, IL-2, IL-4, interferon-gamma, or recombinant human tumor necrosis factor-alpha (rhTNF-alpha) alone. Only the combination of rhTNF-alpha+rIL-1 alpha or rIL-1 beta, and rhTNF-alpha+r IL-1 alpha+IFN-gamma induces some NO production, Human natural anti-pig ant ibodies, which had been described to induce cytoskeleton changes on endothe lial cells, do not induce NO production. Conclusions. Our data show that human monocytes induce the production of NO by gig endothelial cells. The inducing signal is soluble and cannot be pro vided by human anti-pig natural antibodies.