Immunological tolerance and tumour allografts in the brain

Abstract

THE brain has been considered to be an immunologically privileged site with regard to tissue transplantation. In addition, a loss of ‘tumour surveillance’ due to a weakening of the immune system in the brain has been postulated. The data on the brain as a privileged site are not unequivocal, however. The evidence for and against this thesis has been discussed by Woodruff¹ and Lance². Barker and Billingham³ also speculated that “reports that the brain can prevent implanted homografts from inciting sensitivity because it lacks a lymphatic drainage, thus having no afferent pathway of the immunological reflex, are more equivocal”. The need for a critical re-evaluation of the brain as a privileged site has been stressed. We report here a study of the possible action of immunological tolerance in the brain and of the sensitivity of normal rats and tolerant rats to inoculation of allogeneic tumour cells into the brain. We show that transplantation tolerance is involved even in the brain; thus demonstrating the presence of specific immunity following inoculation of tumour cells into the brain. This finding suggests that previously held views of the brain as a privileged site may not be entirely valid and that specific immune processes are accomplished in the central nervous system.