MHC expression in fragment and full-thickness allogeneic embryonic retinaltransplants

Background: The study was carried out to evaluate the expression of major h istocompatibility complex (MHC) molecules in retinal transplants with diffe rent tissue integrity. Methods: Twelve adult rabbits received an allogeneic subretinal neuroretinal transplant, in the form of either fragmented embry onic cells or a complete full-thickness embryonic retina. A controlled tran svitreal approach was used for both transplantation types. The grafts were examined histologically after 31 or 49 days with hematoxylin and eosin stai ning and immunohistochemical analysis of MHC class I and class II expressio n. Results: All five fragment transplants developed into rosettes. Two of t hem displayed MHC class I-labeled cells, and four MHC class II-labeled cell s. The cells were concentrated on the scleral side of the graft, and there was also a marked increase of labeled cells in the choroid. MHC labeling wa s often associated with defects in the retinal pigment epithelium. Six of t he seven full-thickness grafts displayed a laminated morphology with well-d eveloped retinal layers. The seventh consisted of rosettes. None of these g rafts displayed MHC class I- or class II-labeled cells Conclusions: The fin dings suggest that host immune response against fragmented and intact neuro retinal grafts is different, indicating tissue integrity as one factor affe cting graft-host immune interactions. The absence of immune response in ful l-thickness grafts is encouraging and important in the struggle to find the rapies for retinal degenerative disease.