Nitric oxide synthesis in the in vivo allograft response: a possible regulatory mechanism.
Activated macrophages are known to oxidatively metabolize L-arginine to nitric oxide and citrulline. We have recently shown that nitric oxide is a potent inhibitory molecule in the in vitro rat mixed-splenocyte culture, resulting in inhibition of proliferation and cytolytic T-cell induction. We undertook this study using the sponge matrix allograft model in the rat to determine whether nitric oxide plays a role in an in vivo allograft response. Our experiments showed that on day 6 after grafting, when cytolytic activity of allograft-infiltrating cells is first detected, allogeneic graft fluid contains higher levels of NO2-/NO3- (the stable endproducts of nitric oxide metabolism) than syngeneic graft fluid. Furthermore, evaluation of the supernatants of cultured graft-infiltrating cells revealed that allogeneic graft-infiltrating cells spontaneously produce higher amounts of nitric oxide than syngeneic graft-infiltrating cells. The nitric oxide production was inhibited in the presence of NG-monomethyl-L-arginine (NMA), the competitive inhibitor of nitric oxide production. Most of the nitric oxide production was observed in the adherent macrophage fraction of the allograft-infiltrating cells. When allograft-infiltrating cells were cultured in the presence of NMA, donor-specific cytolytic activity was observed, whereas allograft-infiltrating cells cultured in the absence of NMA showed no cytolytic activity. These data show that nitric oxide production may play an important regulatory role in the allograft response.
Langrehr
J M
JM
Department of Surgery, University of Pittsburgh, PA 15261.
Hoffman
R A
RA
Billiar
T R
TR
Lee
K K
KK
Schraut
W H
WH
Simmons
R L
RL
D000818:Animals; D001120:Arginine / Q000031:analogs & derivatives / Q000378:metabolism* / Q000494:pharmacology; D002465:Cell Movement / Q000502:physiology; D003602:Cytotoxicity, Immunologic / Q000502:physiology; D008297:Male; D009569:Nitric Oxide / Q000378:metabolism*; D009609:Nitrous Oxide / Q000378:metabolism; D019736:Prostheses and Implants; D051381:Rats; D011912:Rats, Inbred ACI; D011917:Rats, Inbred Lew; D013154:Spleen / Q000166:cytology; D014184:Transplantation, Homologous / Q000276:immunology / Q000502:physiology*; D019323:omega-N-Methylarginine
D019323:omega-N-Methylarginine; D009569:Nitric Oxide; D001120:Arginine; D009609:Nitrous Oxide