Induction of inducible NO synthase in bystander human T cells increases allogeneic responses in the vasculature

doi:10.1073/pnas.0607731104

Induction of inducible NO synthase in bystander human T cells increases allogeneic responses in the vasculature

*Interdepartmental Program in Vascular Biology and Transplantation,
^§Section of Immunobiology, and
Departments of ^†Pathology,
^¶Dermatology, and
^‡Surgery, Yale University School of Medicine, New Haven, CT 06510

Edited by Richard A. Flavell, Yale University School of Medicine, New Haven, CT, and approved December 1, 2006 (received for review September 6, 2006)

Abstract

Inducible NO synthase (iNOS) in human T cells is implicated in the pathogenesis of graft arteriosclerosis. Here we analyze the regulation and role of iNOS in human peripheral blood T cells. Allogeneic endothelial cells (EC) or dermal fibroblasts induce iNOS mRNA and protein expression, as well as enzymatic activity in primary human CD8 T cells. Although human EC activate T cells through the presentation of alloantigen, iNOS induction is confined to nonactivated T cells and does not depend on MHC molecules or costimulators. iNOS induction does involve new transcription and depends on NF-κB. JAK signaling, initiated during T cell activation, inhibits iNOS expression. Even though iNOS is confined to bystander T cells, inhibition of iNOS activity reduces T cell proliferation in response to allogeneic EC, and addition of low levels of a NO donor rescues T cell responses. Similarly, iNOS is preferentially expressed by nonproliferating T cells within allografted arteries in vivo, and inhibition of iNOS activity reduces the number of activated T cells in these artery segments. These data identify a previously undescribed mechanism for enhanced activation of alloreactive T cells, namely stromal cell-mediated induction of iNOS in bystander T cells.

Footnotes

^‖To whom correspondence should be addressed at:
Boyer Center for Molecular Medicine, 295 Congress Avenue, Room 454, New Haven, CT 06510.
E-mail: jordan.pober{at}yale.edu
Author contributions: J.C.C., G.T., and J.S.P. designed research; J.C.C. and Y.W. performed research; J.C.C. and J.S.P. analyzed data; and J.C.C. and J.S.P. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS direct submission.
This article contains supporting information online at www.pnas.org/cgi/content/full/0607731104/DC1.
Abbreviations:

CFSE,

carboxyfluorescein diacetate succinimidyl ester;

EC,

endothelial cells;

GA,

graft arteriosclerosis;

iNOS,

inducible NO synthase;

PCNA,

proliferating cell nuclear antigen;

PHA,

phytohemagglutinin;

TCR,

T cell receptor.