Inducible nitric oxide synthase promotes cytokine expression in cardiac allografts but is not required for efficient rejection.
BACKGROUND
Inducible nitric oxide synthase (iNOS) is enhanced during acute rejection. Pharmacologic inhibition of nitric oxide synthase (NOS) activity has had variable effects on graft survival in a number of animal models. To further characterize the requirement and effects of iNOS during acute allograft rejection, we examined rejection responses of mice completely deficient of iNOS.


METHODS
Heterotopic cardiac allografts were performed using wild-type and iNOS deficient mice (iNOS[-/-]) as recipients. Graft survival was determined by abdominal palpation. At days 3 and 7 following transplantation, grafts were harvested and analyzed histologically. Cytokine messenger RNA (mRNA) expression was measured by ribonuclease protection assay.


RESULTS
Mean survival time of cardiac allografts did not differ between wild-type (18 +/- 3 days) and iNOS(-/-) recipients (16 +/- 2 days). At 3 days, findings of moderate acute rejection were seen in both recipients groups, although modestly reduced in iNOS(-/ -) mice. By 7 days, allografts in both groups demonstrated severe rejection. Within grafts at day 3, there was a 3-fold reduction in IL-1beta expression and a 4-fold reduction in IL-1RA in iNOS(-/-) recipients (p = 0.03 andp = 0.04, respectively) compared to wild-type recipients. Expression of other proinflammatory cytokines was detected in the grafts from both recipients, but was not significantly different. Finally, rejection responses to iNOS(-/-) cardiac allografts were nearly identical to wild-type allografts.


CONCLUSIONS
Rejection of cardiac allografts by iNOS(-/-) mice occurs in a similar fashion to wild-type recipients, with extensive inflammation and proinflammatory cytokine production. While iNOS may play a role in cytokine induction by macrophages, these studies suggest that iNOS is not required for efficient cardiac graft rejection.
Mannon
R B
RB
Department of Medicine, Duke University Medical Center, Durham, North Carolina 27710, USA. roslyn.mannon@acpub.duke.edu
Roberts
K
K
Ruiz
P
P
Laubach
V
V
Coffman
T M
TM
D000208:Acute Disease; D000818:Animals; D016207:Cytokines / Q000378:metabolism*; D006084:Graft Rejection / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology*; D016027:Heart Transplantation; D053590:Interleukin 1 Receptor Antagonist Protein; D007375:Interleukin-1 / Q000378:metabolism; D051379:Mice; D008815:Mice, Inbred Strains; D009206:Myocardium / Q000473:pathology; D019001:Nitric Oxide Synthase / Q000172:deficiency / Q000502:physiology*; D052247:Nitric Oxide Synthase Type II; D012333:RNA, Messenger / Q000032:analysis; D017472:Receptors, Interleukin-1 / Q000037:antagonists & inhibitors; D012795:Sialoglycoproteins / Q000378:metabolism
D016207:Cytokines; C507764:Il1rn protein, mouse; D053590:Interleukin 1 Receptor Antagonist Protein; D007375:Interleukin-1; D012333:RNA, Messenger; D017472:Receptors, Interleukin-1; D012795:Sialoglycoproteins; D019001:Nitric Oxide Synthase; D052247:Nitric Oxide Synthase Type II; C496317:Nos2 protein, mouse