Cytokine mRNA expression during experimental corneal allograft rejection

Allograft rejection is the main cause of corneal graft failure. T lymphocytes and macrophages have been implied to be involved in corneal rejection, but little is known about the molecular mechanism in this process. In this study, cytokine mRNA expression in the cornea was analysed during experimental corneal transplantation. The donor and acceptor corneas of two groups of rats were studied after receiving an allo- (PVG to AO rat) or autograft (AO rat). For controls, central buttons and peripheral corneal rings of the non-transplanted contralateral eyes were used. At different post-operative days (1, 3, 7, 12 and 19), the corneas were removed and subjected to mRNA isolation. All corneal samples underwent semi-quantitative reverse transcriptase-polymerase chain reaction analysis for interleukin-1 beta, interleukin-1, receptor antagonist, interleukin-2, interleukin-4, interleukin-6, interleukin-10, tumor necrosis factor-alpha, interferon-gamma, monocyte chemotactic protein-1 and macrophage inflammatory protein-2 mRNA expression. Corneal rejection, characterized by opaque corneas with prominent neovascularization, was always diagnosed around day 12. Contralateral, non-grafted corneas showed constitutive mRNA expression for interleukin-1 receptor antagonist and in a few samples also monocyte chemotactic protein-1 and macrophage inflammatory protein-2 mRNA was found. Both allo- and autografts expressed mRNA for the cytokines found in contralateral, non-grafted tissue, as well as for interleukin-1 beta, interleukin-6, interleukin-10 and tumor necrosis factor-alpha. In allografts, the mRNA levels for these cytokines remained constant throughout all post-operative days, with increased interleukin-6 mRNA expression after post-operative day 12. The analysis of the autografts revealed high cytokine mRNA levels until post-operative day 3 or 7, which decreased from then on, except for interleukin-1 receptor antagonist. mRNA for interleukin-2, interleukin-4 and interferon-gamma was not observed in autografts at any time point and in allografts, until post-operative day 12. Interleukin-2 and interferon-gamma mRNA showed maximal expression on POD 12, while in autografts, a marked decrease was observed after POD 3. IL-10 mRNA levels decreased immediately after POD 1 in autografted eyes. For TNF-alpha, an increased mRNA expression starting on POD 7 was found in recipient rings of allografted eyes, while in autografts a weak expression was seen in some samples. MIP-2 transcription increased on PAD 12, while in autografts, its expression was not markedly different from that detected in the contralateral, non-grafted peripheral cornea.