Inducible nitric oxide synthase inhibitors prolonged the survival of skin xenografts through selective down-regulation of pro-inflammatory cytokine and CC-chemokine expressions
Introduction
Nitric oxide (NO) produced by inducible NO synthase (iNOS) is involved in diverse physiologic and pathophysiologic processes which include vasodilation, neurotransmission and immune defense [1], [2]. In the immune system NO displays various effects including antimicrobial [3], [4], anti-tumor [5], [6], [7], immunosuppressive [8], [9], [10], tissue-damaging [11], [12], regulatory effects on cytokine and chemokine expressions [13], [14], [15], [16] and T helper cell deviation [17], [18].
Studies regarding transplantation immunology have demonstrated abundant NO production [19], [20], [21] and significant iNOS induction [22], [23], [24], [25], [26], [27], [28], [29] during allograft rejection. Moreover, iNOS inhibition by potent inhibitors prolongs allograft survival [30], [31], [32] and iNOS activity is attenuated by conventional immunosuppressants [33], [29]. These studies suggest that NO has an immunoregulatory property in allotransplantation. However, the possible immunoregulatory role of NO in the xenotransplant rejection process, where innate immunity may play a more potent role than in the allotransplant rejection process has not been elucidated. Therefore, we examined the effects of iNOS inhibitors on the immune cell infiltration and the expressions of cytokines and chemokines in rat-to-mouse xenogeneic skingraft rejection.
Section snippets
Animals
Four- to six-week-old female C57BL/6J (B6) mice and 6-week-old Lewis female rats were purchased from Jackson Laboratory (Bar Harbor, ME) and bred in a specific pathogen-free facility in Seoul National University College of Medicine Animal facilities. In vivo experimental protocols were approved by the Animal Ethics Committee and were performed according to institutional guidelines.
Skingrafting
Donor tail skin was grafted as previously described [34]. In brief, mice anesthetized with avertin were grafted
Expressions of iNOS protein and mRNA in skin xenografts
B6 mice were grafted with B6, BALB/c or rat tail skin onto the lateral thoracic region and the grafts were harvested on days 3, 5, 7 and 9 after grafting and subjected to Western-blot and real-time RT-PCR analysis for iNOS. As shown in Fig. 1, iNOS in the xenograft was found to be significantly induced in terms of protein (a) and mRNA (b) synthesis 7 and 9 days after grafting, whereas in iso- and allograft their inductions were negligible throughout the transplantation period.
Effects of iNOS inhibitors on the survival of skin xenograft
To elucidate the
Discussion
In previous reports, modulation of NO production after organ transplantation by administration of iNOS inhibitor produced different outcome; in cardiac and aortic allotransplantation, iNOS plays a protective role by suppressing the development of arteriosclerosis [29], while in the case of renal allografts, the inhibition of iNOS attenuates tubulointerstitial injury and improves graft function and survival [35]. These reports reflect that NO can play an opposite role under given circumstances.
Acknowledgements
This study was supported by a grant (01-PJ1-PG3-21200-0044) of the Good Health R & D Project. Ministry of Health and Welfare, Republic of Korea.
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