Evidence that T-Helper Type 2 Cell-Derived Cytokines and Eosinophils Contribute to Acute Rejection of Orthotopic Corneal Xenografts in Mice

BACKGROUND: Because guinea pig corneal xenografts are rejected acutely (within 16 days) in mouse eyes by a T-cell-dependent mechanism, the authors wished to determine the functional phenotype of CD4+ effector T cells. METHODS: Orthotopic corneal xenotransplantation was performed from strain 13 guinea pigs to BALB/c mice. Grafted eyes were removed at specified times and examined histologically or subjected to cytokine and chemokine mRNA analysis using a multi-probe ribonuclease protection assay. Draining cervical lymph node cells were harvested at specified times and stimulated in vitro with x-irradiated strain 13 guinea pig spleen cells. Supernatants were assayed by enzyme-linked immunosorbent assay for content of interleukin (IL)-2, interferon (IFN)-gamma, IL-4, IL-5, and IL-10 and cells were used for mRNA analysis. RESULTS: Rejected corneal xenografts were heavily infiltrated with polymorphonuclear leukocytes, the majority of which were eosinophils. These eyes contained mRNA for IL-4, IL-6, IL-10, IL-13, IL-15, and IFN-gamma. When stimulated with guinea pig spleen cells, T cells from draining cervical lymph nodes secreted primarily IL-4, IL-5, IL-10, and IFN-gamma. Eotaxin was overexpressed in eyes with rejected corneal xenografts. CONCLUSIONS: Acute rejection of corneal xenografts in mice is mediated by T cells that display a mixed T-helper (Th) type 2/Th1 phenotype and secrete eotaxin, an eosinophil chemoattractant. Eosinophil-dependent xenograft rejection bears similarities to immune elimination of parasites.