Interleukin-12 (IL-12)-driven alloimmune responses in vitro and in vivo: requirement for beta1 subunit of the IL-12 receptor.
BACKGROUND
Interleukin-12 (IL-12) mediates its biologic activities via binding high-affinity receptors on T and natural killer cells. Although emphasis has been placed on the requirement for IL-12Rbeta2 in IL-12 bioactivity, the role of IL-12Rbeta1 is less well defined. The current study evaluated the effects of exogenous IL-12 on alloantigen-specific immune responses and determined the requirement for IL-12Rbeta1 in IL-12-mediated alloimmunity.


METHODS
The mouse heterotopic cardiac transplant model was employed to evaluate the effects of IL-12 on alloantigen-specific immune responses in vivo. In addition, IFN-gamma production in mixed lymphocyte cultures (MLC) supplemented with IL-12 was measured to assess the effects of IL-12 on Th1 function in vitro. Mice deficient in IL-12Rbeta1 (IL-12Rbeta1-/-) were used to determine the requirement for this receptor component in IL-12-driven alloimmune responses.


RESULTS
Addition of IL-12 to MLC consisting of wild-type splenocytes enhanced alloantigen-specific proliferative responses and Th1 development. In contrast, IL-12 did not alter these in vitro immune parameters in IL-12Rbeta1-/- MLC. Treatment of wild-type cardiac allograft recipients with IL-12 resulted in high concentrations of serum interferon-gamma (IFN-gamma) and a 10-fold increase in IFN-gamma production by recipient splenocytes after restimulation in vitro. However, this fulminate Th1 response did not accelerate allograft rejection. Importantly, IL-12 had no effect on serum IFN-gamma or in vivo priming of Thl in IL-12Rbeta1-/- recipients. Finally, administration of IL-12 to WT allograft recipients resulted in a bimodal alloantibody response: antibody production was suppressed at high doses of IL-12, and enhanced at lower doses.


CONCLUSIONS
IL-12 markedly enhances alloantigen-specific immune function; however, these exaggerated Th1-driven responses do not culminate in accelerated allograft rejection. Further, these data indicate that IL-12Rbeta1 is essential for the enhancement of both in vitro and in vivo alloimmune responses by exogenous IL-12.
Piccotti
J R
JR
Department of Surgery, University of Michigan School of Medicine, Ann Arbor 48109-0654, USA.
Li
K
K
Chan
S Y
SY
Eichwald
E J
EJ
Bishop
D K
DK
D000818:Animals; D000917:Antibody Formation / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D000939:Epitopes / Q000276:immunology; D005260:Female; D006084:Graft Rejection / Q000188:drug therapy; D016027:Heart Transplantation / Q000276:immunology; D018664:Interleukin-12 / Q000378:metabolism / Q000494:pharmacology*; D007519:Isoantigens / Q000235:genetics / Q000276:immunology*; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D010641:Phenotype; D018123:Receptors, Interleukin / Q000378:metabolism*; D011994:Recombinant Proteins / Q000494:pharmacology; D018417:Th1 Cells / Q000502:physiology; D014184:Transplantation, Homologous / Q000502:physiology
D000939:Epitopes; D007519:Isoantigens; D018123:Receptors, Interleukin; D011994:Recombinant Proteins; D018664:Interleukin-12