Chapter 15 - Immunologic Privilege and the Brain

Abstract

This chapter describes the immunologic privilege and the brain. The central nervous system (CNS) is one of several anatomic sites considered to be immunologically privileged. Perhaps the best-defined immunologically privileged site is the placenta. Since the discovery of histocompatibility, scientists have puzzled over the factors that underlie a fetus' ability to survive in a histo-incompatible environment. Other immunologically privileged sites include the anterior chamber and cornea of the eye, the testis, and the hamster cheek pouch. With the exception of the placenta, this designation derives from observations dating to the early twentieth century regarding the behavior of foreign tissues transplanted to these sites. The properties that contribute to immunologic privilege are complex. It is important to bear in mind that such privilege is relative and not absolute. As such, immunologic privilege should be thought of as dynamic rather than static in nature. For example, although immune responses in the brain are limited by a variety of factors, continuous immune surveillance is essential to the general health of the CNS.