Background.

The relative contribution of pro-inflammatory and anti-inflammatory cytokines in promoting the rejection or acceptance of experimental cardiac allografts remains controversial. We hypothesized that the posttransplantation induction of a new immune response to graft alloantigens at a distant delayed-type hypersensitivity (DTH) site would force the immune system to reveal its current disposition toward graft alloantigen as it initiates the new immune response. Thus, we should be able to monitor the evolution of the immunologic relationship between allograft recipients and their grafts at any time posttransplantation by challenging the recipient for DTH responses to donor alloantigen and evaluating the cytokine profiles displayed at the DTH site.

Methods.

We have used the sensitive and quantitative technique of real-time polymerase chain reaction to evaluate the patterns of donor alloantigen-induced cytokine mRNA production for interleukin (IL)-2, interferon (IFN)-γ, IL-4, IL-10, and transforming growth factor (TGF)-β. We evaluated cytokine mRNA expression in cardiac allografts and in donor alloantigen-challenged DTH sites in mice that have either accepted or rejected cardiac allografts.

Results.

We observed the following.(1) Normal hearts and pinnae exhibited detectable baseline production of cytokine mRNAs: TGF-β> IFN-γ= IL-10> IL2-> IL-4.(2) Both the accepted and rejecting cardiac allografts produced increased amounts of all cytokine mRNAs tested and displayed few quantitative differences in cytokine mRNA production. Notably, accepted allografts displayed enhanced IL-10 mRNA production on day 7 posttransplantation, but not on day 60 posttransplantation and reduced IFN-γ mRNA production on day 60, but not day 7.(3) There was a high degree of variability in production levels among the various cytokine mRNAs, both for background levels and for allograft-stimulated levels.(4) Donor-reactive DTH sites of allograft rejector mice displayed a broad array of cytokine mRNAs, whereas the DTH sites of allograft acceptor mice displayed only IL-4 mRNA production.(5) Provision of exogenous TGF-β or IL-10 at a DTH challenge site of allograft rejector mice caused a shift in the cytokine mRNA profile that minimized IFN-γ and IL-2 mRNA production but spared IL-4, IL-10, and TGF-β mRNA production.

Conclusions.

A broad array of cytokine mRNAs may be stockpiled for future use in cardiac allografts, regardless of whether the grafts will be accepted or rejected. This stockpile is continuously replenished for as long as the graft survives, thereby obscuring any changes in immune disposition of the graft recipient toward graft alloantigens. However, such changes can be revealed by challenge with donor alloantigens at a distant site (DTH challenge). In allograft acceptor mice, this disposition evolves from pro-inflammatory to anti-inflammatory.