Background: Allogeneic rejection is the most common cause of corneal graft failure. The aim of this work was to establish the kinetics of cytokine and chemokine mRNA expression before and after onset of corneal graft rejection.

Methods: Intracorneal cytokine and chemokine mRNA levels were investigated in the Brown Norway-->Lewis inbred rat model in which rejection onset is observed at 8/9 days after grafting in all animals. Nongrafted corneas and syngeneic (Lewis-->Lewis) corneal transplants were used as controls. Donor and recipient cornea was examined by quantitative competitive reverse transcription-polymerase chain reaction (RT-PCR) for hypoxyanthine phosphoribosyltransferase (HPRT), CD3, CD25, interleukin (IL)-1beta, IL-1RA, IL2, IL-6, IL-10, interferon-gamma (IFN-gamma), tumor necrosis factor (TNF), transforming growth factor (TGF)-beta1, and macrophage inflammatory protein (MIP)-II and by nonquantitative RT-PCR for IL4, IL-5, IL-12 p40, IL-13, TGF-beta2, monocyte chemotactic protein-1 (MCP-1), MIP-1alpha, MIP-1beta, and RANTES (for regulated upon activation normal T cell expressed and secreted).

Results: A biphasic expression of cytokine and chemokine mRNA was found after transplantation. During the early phase (days 3-9), there was an elevation of the majority of the cytokines examined, including IL-1beta, IL-6, IL-10, IL-12 p40, and MIP-II. There was no difference in cytokine expression patterns between allogeneic or syngeneic recipients at this time. In syngeneic recipients, cytokine levels reduced to pretransplant levels by day 13, whereas levels of all cytokines rose after observed rejection onset in the allografts, including TGF-beta1, TGF-beta2, and IL-1RA. The T cell-derived cytokines IL-4, IL-13, and IFN-gamma were detected only during the rejection phase in allogeneic recipients.

Conclusions: There is an early cytokine and chemokine response to the transplantation process, evident in syngeneic and allogeneic grafts, that probably drives angiogenesis, leukocyte recruitment, and affects leukocyte functions. After an immune response has been generated, allogeneic rejection results in the expression of Th1 cytokines (IL-2, IL-12 p40, IFN-gamma), Th2 cytokines (IL-4, IL-6, IL-10, and IL-13), and antiinflammatory/Th3 cytokines (TGF-beta1/2 and IL-1RA).