Fate of orthotopic corneal allografts in eyes that cannot support anterior chamber-associated immune deviation induction.

PURPOSE Corneal allografts placed in human eyes at high risk often fail, and immune rejection is thought to be a major pathogenic factor. To understand the immunologic factors responsible for rejection in this instance, the authors have created "high-risk" eyes in mice by inducing corneal neovascularization. The authors then examined the fate of orthotopic corneal grafts placed in these beds and assessed the development of donor-specific delayed hypersensitivity (DH) in recipient mice. METHODS Three interrupted sutures were placed in the central cornea of recipient BALB/c mice to induce corneal neovascularization. Two weeks later, when corneal vessels occupied more than two quadrants of the cornea, mice received orthotopic corneal grafts from donor mice expressing alloantigens encoded by major and minor histocompatibility loci. Corneal allografts were evaluated by slit-lamp examination after grafting, and recipient mice were examined at the time of the rejection to determine whether they had acquired DH to alloantigens expressed on the corneal grafts. RESULTS Compared to grafts placed in normal eyes, a much higher incidence of rejection was observed among corneal allografts placed in neovascularized eyes (96.7% versus 46.7%). Moreover, grafts in neovascularized beds were rejected much more swiftly (2 weeks versus > 3 to 4 weeks). Rejection of corneal allografts in high-risk eyes coincided temporally with development of intense donor-specific DH, and the specificity of this immune response was directed solely at minor H antigens (not major histocompatibility complex-encoded antigens) on the graft. CONCLUSIONS These results indicate that eyes rendered high risk by virtue of corneal neovascularization fail to provide immune privilege for orthotopic corneal allografts. In this circumstance, the grafts rapidly induce intense donor-specific DH that is readily detectable within 2 weeks of engraftment, at which time the grafts are acutely and universally rejected. The recipient DH response is directed exclusively at minor H antigens on the graft, which is consistent with the view that neovascularization creates graft beds in which recipient antigen-presenting cells infiltrate the graft and carry antigenic information by lymphatics to draining lymph nodes. In this manner, anterior chamber-associated immune deviation is avoided, and potentially allodestructive DH is promoted.