Survival and MHC-expression of embryonic retinal transplants in the choroid

To study the survival of syngenic versus allogenic embryonic retinal transplants in the choroid, and try to correlate the survival to the expression of MHC-expression and the presence of activated microglia.

Fetal neural retinas of Sprague-Dawley (SD) rats were implanted in the choroid of adult Lewis and SD rats. After 3 weeks the retina, the choroid and the transplants were examined by light microscope and evaluated with antibodies against MHC class I and II.

Retinal transplants were found in all eyes. The transplants had one subretinal and one choroidal component. The syngenic transplants thrived in the subretinal space and formed rosettes and the choroidal components had to some extent rosette formation, though not as distinct as in the subretinal part. Almost no upregulation of MHC class I and II was seen. The allogenic transplants were totally deranged in the subretinal space as well as in the choroid. There was a marked upregulation of MHC class I, most pronounced in the transplants, but also in the host retina. Numerous MHC class II positive cells were seen in the transplants, but also in the host retina. All of these cells were dendritic and had the typical appearance of microglia.

Syngenic choroidal transplants were seen to grow and thrive, whereas the allogenic transplants were rejected. There is a considerable upregulation of MHC expression in the allogenic transplants, but not in the syngenic.