Morphological studies on avian spinal cord chimeras.

Spinal cord chimeras were constructed by orthotopic grafting of quail embryonal neutral folds, neural crest and neural tube into chicken embryos. The spinal cord xenografts were accepted for varying lengths of time, but most chimeras eventually rejected the quail transplant. This was associated with perivenular cuffing and demyelination with preservation of most neurons, as well as clinical neurological symptoms. Twenty-four chimeras were studied to delineate the time of first appearance of glial deposits of immunoglobulin and to identify the subpopulations of T cells in spinal cord infiltrates. The results suggested that deposits of immunoglobulins on glial elements preceded inflammatory cell infiltration. The perivenular cuffs consisted predominantly of T cells and showed a preponderance of CD8- over CD4-positive cells (CD4/CD8 ratios around 0.6). Further, CD4+ cells were found almost exclusively in the central portions of the infiltrate, with the periphery consisting almost only of CD8+ cells. The diffuse cellular infiltrate of the parenchyme contained T and plasma cells. The T cells were almost exclusively CD8+. Plasma cells were seen only at the outer borders of the cuffs and dispersed throughout the quail-derived spinal cord tissue. It seemed that rejection of quail-derived melanocytes in feathers ('quail-like feathers'), described by us earlier, often preceded neurological symptoms and showed a histopathological pattern comparable to spinal cord lesions, i.e., predominantly perivascular cuffing. In preliminary studies, enhancement of disease by immunization with quail organ suspension and decreased intensity of disease by combined immunosuppressive treatment with FK 506 and cycylophosphamide were suggested. The data presented here are compatible with the hypothesis that rejection of CNS quail tissue by chimeras is preceded in the periphery by rejection of melanocytes in segments of skin and in feathers, and that the spinal cord rejection relies on xenoantibodies and on cytotoxic as well as delayed hypersensitivity-type T cells. Finally, these data strengthen the analogy between the histopathologic presentation and immune effector composition of the xenograft rejection lesions in the chimeras and the plaques seen in patients with multiple sclerosis.