[Effect of topical dexamethasone treatment on antigen-presenting cells in murine corneas]

To determine the influence of dexamethasone treatment on APCs and the time of graft survival of MHC-disparate grafts.

Flatmounts of the ocular surface prepared with EDTA and tangential frozen sections of the remaining corneal stroma from untreated eyes of normal mice (n=6) and from eyes treated for 7 days with dexamethasone ( n=6) were immunohistologically examined for content of F4/80+ and MHC II+ cells.Furthermore, corneas of C(3)H mice without and with 7-day dexamethasone eye drop treatment (n=8) were grafted into BALB/c mice receiving the same treatment.

The number of positive cells within the epithelial flatmounts showed a dramatic reduction in the dexamethasone-pretreated group (p<0.01 compared to the untreated control group). The number of positive cells in the corneal stroma remained unchanged. The grafts of untreated control mice survived 16+/-4 days, the treated grafts 16+/-3 days.

Most investigators assume that normal murine corneas contain no APCs such as macrophages and Langerhans cells. For the first time we were able to detect APCs in flatmounts of the ocular surface and frozen sections of corneal stroma. Our investigations show that, in contrast to the ocular surface, the number of F4/80+ cells in the corneal stroma is not influenced by dexamethasone treatment. Transplantation of corneas containing donor-derived APCs promotes acute rejection (direct pathway of allorecognition).Thus,dexamethasone treatment did not prolong the time of allograft survival.