Is the Brain "An Immunologically Privileged Site?"

THE CONCEPT of the as an immunologically privileged site has come about as a result of the investigations of Medawar 1 and Greene. 2-4 Medawar 1 showed that the does not respond with the typical primary or secondary set reaction histologically when homologous skin is implanted in the cerebrum. Greene 2-4 demonstrated that the will accept tumor homotransplants or heterotransplants which were rejected when transplanted to other sites under ordinary circumstances. These phenomena and the failure to demonstrate lymphatic channels in the have led to the concept that the is an immunologically privileged site. Scheinberg et al 5,6 have subsequently demonstrated that this immunologic privilege of the brain appears to be far from perfect. In their initial studies 5 they demonstrated a variable acceptance of tumor homotransplants by the with rejection of all tumor homotransplants by the subcutaneous tissues. Tumor isotransplants were almost