Amplified Natural Killer Cell Activity and Attenuated Regulatory T-cell Function Are Determinants for Corneal Alloimmunity in Very Young Mice.

Background: Corneal transplantation outcomes are generally less favorable in young children compared with adults. The purpose of this study was to determine the immunological mechanisms underlying this difference.

Methods: A murine model of allogeneic corneal transplantation was used in the study, and graft survival was determined by evaluating opacity scores for 8 wk. Syngeneic transplantation in the very young host served as a surgical control. The frequencies of total and activated natural killer (NK) cells in cornea posttransplantation were kinetically evaluated using flow cytometry. The regulatory T cell (Treg) frequency and function in naive animals were assessed by flow cytometry and in vitro suppression assays, respectively. Finally, graft survival and immune responses were determined in NK cell-depleted, or adult naive Treg-transferred, young hosts.

Results: Corneal allograft survival in the very young recipients was significantly lower than in adult hosts. The frequencies of total NK cells and their interferon gamma-expressing subset in the cornea were significantly higher in the very young mice posttransplantation. In ungrafted mice, frequencies of Treg in draining lymph nodes as well as their capabilities to suppress NK-cell secretion of interferon gamma were lower in the very young compared with adults. In NK cell-depleted or adult Treg--transferred very young recipients, the allograft survival was significantly improved along with the suppressed NK-cell response.

Conclusions: Our data demonstrate that amplified activity of NK cells, together with lower suppressive function of Treg, contributes to early rejection of corneal allografts in very young graft recipients.