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MICA INHIBITS NK CELL RESPONSES TO PORCINE ENDOTHELIAL CELLS MEDIATED BY NKG2D.
S. Ramachandran Ph.D 1, N. Stewart M.S. 1, W. Chapman M.D. 1, N. Babinsky 1 and T. Mohanakumar Ph.D 1,2. 1 Surgery, Washington University School of Medicine and 2 Pathology & Immunology, Washington University, St Louis, MO, USA .
Xenotransplantation offers a potential alternative to donor organ shortage. NK cells play an important role in xenograft rejection. NK cells express both activating and inhibiting receptors. The aim of the study was to identify the activating receptor involved in activation of NK cells on exposure to porcine aortic endothelial cells and study the effect of MICA on NK cell activation.
Human NK cells were purified from PBMCs by Rossettesep NK cell enrichment kit. Expression profiles of activating receptors NKp46, NKp44, NKp30 and NKG2D on exposure to PAEC were analyzed by RT-PCR, western blot and FACS. Effect of MICA on NK cell responses were studied by adding purified human recombinant MICA protein to cultures.
Purified human NK cells were able to significantly lyse (44.4%) PAEC compared to HAEC. Incubation of NK cells with PAEC resulted in increased expression of NKG2D. FACS analysis of activated NK cells showed 3-fold increase in number of NKG2D+ NK cells. Treatment with soluble MICA, a ligand for the NKG2D receptor resulted in significant inhibition (79%) of PAEC cytotoxicity and cytokine secretion (Figure 1).
In conclusion, human NK cells recognize PAEC through NKG2D leading to cytotoxicity and cytokine secretion. Addition of MICA significantly inhibits NK cell cytotoxicity and IFN-
secretion, providing a potential avenue for inhibition NK cell mediated acute xenograft rejection.