Lysis of pig endothelium by IL-2 activated human natural killer cells is inhibited by swine and human major histocompatibility complex (MHC) class I gene products.
We have previously described a form of xenograft rejection, mediated by natural killer (NK) cells, occurring in pig-to-primate organ transplants beyond the period of antibody-mediated hyperacute rejection. In this study, two distinct NK activation pathways were identified as mechanisms of pig aortic endotheliual cell (PAEC) lysis by human NK cells. Using an antibody-dependent cellular cytotoxicity (ADCC) assay, a progressive increase in human NK lysis of PAEC was observed following incubation with human IgG at increasing serum titer. In the absence of IgG, a second mechanism of PAEC lysis by human NK cells was observed following activation with IL-2. IL-2 activation of human NK cells increased lysis of PAEC by over 3-fold compared with ADCC. These results indicate that IL-2 activation of human NK cells induces significantly higher levels of lytic activity than does conventional ADCC involving IgG and FcRIII. We next investigated the role of MHC class I molecules in the regulation of NK lysis following IL-2 activation. PAEC expression of SLA class I molecules was increased by up to 75% by treatment with human TNFa. Following treatment with TNFa at 1 u/ml, IL-2 activated human NK lysis of PAEC was inhibited at every effector:target (E:T) ratio tested. Maximal effect occurred at an E:T ratio of 10:1, with TNFa inhibiting specific lysis by 59% (p < 0.01). Incubation with an anti-SLA class I Mab, but not IgG isotype control, abrogated the protective effects of TNFa on NK lysis of PAEC, suggesting direct inhibitory effects of SLA class I molecules on human NK function. To investigate whether human MHC class I molecules might have similar effects on human NK lysis of PAEC, further experiments were performed using a soluble peptide derived from the alpha-helical region of HLA-B7. Incubation with the HLA-B7 derived peptide significantly reduced the IL-2 activated NK lytic activity against PAEC in a dose-dependent fashion. Maximal effect occurred at a concentration of 10 mg/ml, where an 8-fold reduction in IL-2 augmented NK lysis was observed (p < 0.01). These results suggest that IL-2 activated human NK lysis of porcine xenografts may be inhibited by strategies which increase PAEC expression of SLA class I molecules, introduce HLA class I genes into PAEC, or use soluble HLA class I peptides.
Itescu
S
S
Columbia University College of Physicians and Surgeons, New York, NY, USA.
Artrip
J H
JH
Kwiatkowski
P A
PA
Wang
S F
SF
Minanov
O P
OP
Morgenthau
A S
AS
Michler
R E
RE
D000818:Animals; D000920:Antibody-Dependent Cell Cytotoxicity / Q000187:drug effects / Q000276:immunology; D001011:Aorta / Q000276:immunology; D002478:Cells, Cultured; D003602:Cytotoxicity, Immunologic / Q000187:drug effects*; D004730:Endothelium, Vascular / Q000276:immunology*; D006084:Graft Rejection / Q000276:immunology; D015793:HLA-B7 Antigen / Q000276:immunology; D015395:Histocompatibility Antigens Class I / Q000276:immunology*; D006801:Humans; D007376:Interleukin-2 / Q000494:pharmacology*; D007694:Killer Cells, Natural / Q000187:drug effects / Q000276:immunology*; D007963:Leukocytes, Mononuclear / Q000276:immunology; D008213:Lymphocyte Activation / Q000187:drug effects; D013552:Swine; D014183:Transplantation, Heterologous / Q000276:immunology; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology
D015793:HLA-B7 Antigen; D015395:Histocompatibility Antigens Class I; D007376:Interleukin-2; D014409:Tumor Necrosis Factor-alpha