Cytokine expression during orthotopic corneal allograft rejection in mice.

PURPOSE The acquisition of cell-mediated immunity against donor antigens has been shown to be associated with rejection of orthotopic corneal allografts, but the mechanisms that cause corneal allograft destruction in grafted tissue remain obscure. To determine which T-cell subsets infiltrate graft tissue and cause graft rejection, cytokine expression was examined in corneal tissue after orthotopic corneal allograft. METHODS BALB/c mice received orthotopic corneal allografts from either syngeneic BALB/c or allogeneic C57BL/6 donors. At 1 or 4 weeks after grafting, the mice were euthanatized, and their corneas were removed. Corneal tissue was frozen, homogenized, and placed in phosphate-buffered saline (PBS). Each sample consisted of five corneas in 500 ml PBS. After centrifugation, the supernatant was collected, and the concentration of the following cytokines was measured by enzyme-linked immunosorbent assay: interleukin (IL)-1alpha, IL-2, IL-4, IL-10, interferon (IFN)-gamma, and tumor necrosis factor (TNF)-alpha. RESULTS Significantly increased amounts of proinflammatory cytokines (IL-1alpha and TNF-alpha) were detected in supernatants from all grafted corneas (both syngeneic and allogeneic) at 1 week after grafting. At 4 weeks after grafting, supernatants from normal corneas, corneas with syngeneic grafts, and corneas with accepted corneal allografts contained undetectable amounts of IL-2 and IFN-gamma, whereas supernatants from corneas with rejected corneal allografts contained significant amounts of IL-2 and IFN-gamma. There were no significant differences in the amounts of IL-4 or IL-10 among all samples. Histologic examination confirmed the expression of IL-2 and IFN-gamma in rejected corneal allografts. CONCLUSIONS Because IL-2 and IFN-gamma are secreted primarily by T-helper type 1 (Th 1) cells, whereas IL-4 and IL-10 are secreted by T-helper type 2 (Th 2) cells, these results indicate that Th 1-type cytokines, rather than Th 2-type cytokines, contribute to the rejection of orthotopic corneal allografts in graft tissue.