Transplantation immunobiology of the cornea

Transplantation of the cornea presents the immunologist with a set of conditions which are unique in transplant biology, with respect to both donor tissue and recipient bed. These include : (1) the normal avascularity of the cornea; (2) the simplified anatomy of its layered structure; (3) the ability to exclude from the graft certain tissue elements (endothelium from lamellar grafts and epithelium from all grafts); (4) the ability to transplant dead tissue successfully (the stroma); and (5) the special sensitivity of the penetrating graft to any embarrassment of its endothelium. These features are considered in a review of the experimental evidence for the survival of the separate cell layers of the cornea, their antigenicity, and the manner in which they may suffer rejection. The effects of these special features of corneal anatomy and physiology on the afferent arc of host sensitization as well as on the efferent arc of allograft rejection are also examined. Finally, it is pointed out that the typical patterns of epithelial, stromal or endothelial rejection constitute pathognomonic indicators of the specific allograft rejection process.