Interleukin-12p70 prolongs allograft survival by induction of interferon gamma and nitric oxide production.
BACKGROUND
Interleukin (IL)-12p70, a heterodimeric cytokine has been considered central to induction of Th1 responses with the assistance of IL-18 and IL-27. It was predicted IL-12p70 treatment would promote allograft rejection. In these studies, IL-12p70 delayed rejection.


METHODS
We compared Piebald Virol Glaxo (PVG) neonatal heart graft survival in fully allogeneic Dark Agoutti (DA) rats treated with IL-12p70 alone or in combination with other cytokines. The mechanism by which IL-12p70 induced delayed rejection was examined by reverse transcription polymerase chain reaction of cytokine mRNA and studying the role of interferon (IFN)-gamma and inducible nitric oxide synthase (iNOS) that were induced by IL-12.


RESULTS
IL-12p70 treatment significantly delayed PVG neonatal heart graft rejection compared to normal rejection control and other control groups treated with supernatant from Chinese hamster ovary (CHO)-K1 cells transfected with IL-12p35, IL-12p40, or no cytokine gene. IL-12p70 had no effect on alloantibody response. IFN-gamma and iNOS mRNA expression was increased in heart graft and regional lymph node compared to normal rejection and other treatment groups, consistent with Th1 response induction. IL-12p35 mRNA expression decreased in IL-12p70 treated rats but there was no difference in IL-12p40, Th2, or Tr1 cytokine mRNA expression. Coadministration of an iNOS inhibitor, L-NIL, or a monoclonal antibody (mAb) that blocks IFN-gamma, inhibited IL-12p70's ability to prolong allograft survival; as did co-treatment with IL-4 but not IL-13.


CONCLUSIONS
IL-12p70 treatment may inhibit rejection by hyperinduction of Th1 responses, especially production of IFN-gamma and nitric oxide. These effects may be by enhancing regulatory T-cell responses or by the activation of iNOS in macrophages to produce excessive nitric oxide that in turn inhibits alloimmune responses.
Verma
Nirupama D
ND
Department of Medicine, Immune Tolerance Group, University of New South Wales, New South Wales, Australia. n.verma@unsw.edu.au
Boyd
Rochelle
R
Robinson
Catherine
C
Plain
Karren M
KM
Tran
Giang T
GT
Hall
Bruce M
BM
D000818:Animals; D000831:Animals, Newborn; D003433:Crosses, Genetic; D016207:Cytokines / Q000235:genetics; D006085:Graft Survival / Q000187:drug effects / Q000276:immunology / Q000502:physiology*; D016027:Heart Transplantation / Q000276:immunology / Q000502:physiology*; D007371:Interferon-gamma / Q000096:biosynthesis*; D018664:Interleukin-12 / Q000627:therapeutic use*; D018793:Interleukin-13 / Q000627:therapeutic use; D015847:Interleukin-4 / Q000627:therapeutic use; D007518:Isoantibodies / Q000097:blood; D023421:Models, Animal; D009569:Nitric Oxide / Q000096:biosynthesis*; D012333:RNA, Messenger / Q000235:genetics; D051381:Rats; D011919:Rats, Inbred Strains; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014184:Transplantation, Homologous
D016207:Cytokines; D018793:Interleukin-13; D007518:Isoantibodies; D012333:RNA, Messenger; D018664:Interleukin-12; D015847:Interleukin-4; D009569:Nitric Oxide; D007371:Interferon-gamma