Do immunologically privileged sites require a functioning spleen?

Abstract

WHEN solid tissue allografts are transplanted orthotopically to alien hosts they are rejected with a characteristic tempo and vigour that depends primarily on the immunogenetic disparity between donor and host. There are, however, several anatomical sites in which prolonged graft survivals have been documented. These so-called immunologically privileged sites include the brain1,2, anterior chamber (AC) of the eye3–5, cheek pouch of the Syrian hamster6 and artificially created skin pedicle flaps in guinea pigs and rats7,8. There is considerable experimental evidence that these sites share at least one common feature—absence of a demonstrable lymphatic drainage7–9. As a consequence, it has been assumed that the putative immunological privilege of these diverse sites results from the anatomical aberration which interrupts the afferent limb of the immunological reflex arc (which is composed of an afferent limb, a central mechanism and an efferent limb). We have now found that allogeneic cells placed within the AC of the eye are not isolated from the immunological apparatus of the host, but instead induce a primary immune response within the spleen which alters the systemic immunological response of the intact animal.