Embryonic rabbit retinal transplants survive and differentiate in the choroid

Retinal allotransplants to intraocular locations usually survive well, partly because of the relative immune privilege provided by the blood-ocular barriers. The choroid, however, is located outside the barriers, and is therefore usually considered not to be immunologically privileged. This study was performed to investigate if transplants could survive in the choroid, and, if so, if they develop some sort of blood transplant barrier. Embryonic retinas from pigmented rabbits at stage E 15 (embryonic day 15) or E 22 were dissected and transplanted into the choroid of 29 adult animals of the same strain. As controls, a similar retinal transplant was placed in the subretinal space in six animals and in the subconjunctival space in another six animals. The animals were killed at intervals up to 8 weeks and the eyes were analysed by light microscopy, immunohistochemistry and morphometry. Some of the animals received Evan's Blue intravenously before termination. Eighty-three per cent of the choroidal transplants survived until termination. All six subretinal but none of the six subconjunctival transplants survived. Both choroidal and subretinal grafts developed rosettes, i.e. rounded formations of retinal cells organized in layers. The different retinal cells developed normal reactivity for the intracellular markers rhodopsin, neurofilament 160 kDa, vimentin and GFAP. Evan's Blue and endogenous serum albumin were used as markers for the patency of the blood-ocular barriers. Evan's Blue was not excluded from the transplants in the early phase up to day 8 after the transplantation. The Evan's Blue content diminished with longer survival times, and after 40 days almost no Evan's Blue was present in the transplants.(ABSTRACT TRUNCATED AT 250 WORDS)