We have been studying selected immunohistological staining patterns of intraventricular tissue grafts in host brains and adrenal medullae in situ and in vitro. We have attempted to determine the essential factors involved in the development and survival of these tissues. Results indicate that the expression of cell adhesion molecules (CAMS) in transplanted cerebella is relatively undisturbed, and that genetically normal cerebellar grafts can survive in a mutant host environment defective in CAMs and myelination. We have also found that intraventricular grafts, as compared to intraparenchymal rats are not as well integrated with host brains, and that CAMs are present in rat adrenal medullae in situ. In tissue cultures, the outgrowth of fibers on chromaffin cells is associated with an enhancement of L1 and N-CAM on their neurites. Transplanted, surviving adrenal medulla fragments within the lateral ventricle of the host rat demonstrated an enhancement of L1 expression which was accompanied by a reorganization of the closely associated extracellular matrix. Other data suggest that only in xenografts does an intense host reaction occur that is capable of destroying transplanted tissue. MHC class II immunoreactivity is enhanced in host parenchyma on microglial cells, but not on GFAP positive astrocytes after iso, allo and xenografting. Genetic disparity does not seem to be the only factor affecting the survival of allogenic neural grafts, with or without systemic sensitization, and, in fact, plays only a relatively limited role. Susceptibility to neural graft rejection may depend on immunogenicity of the donor, Ir gene, host allele, and host susceptibility to autoimmune disease.
