INDUCTION OF TOLERANCE VIA THE RESPIRATORY MUCOSA

Immunological tolerance is defined as a state of specific non-responsi veness to a particular antigen induced by previous exposure to that sa me antigen. The mucosal surfaces comprise the upper and lower respirat ory tracts, the gastrointestinal tract and the urogenitary tract, and are a major site of antigenic challenge. The immune system associated with the mucosa has the extraordinary potential to discriminate betwee n antigens that are harmless (e.g. inhaled and dietary antigens) and t hose that are associated with pathogens. Normally soluble proteins del ivered through the mucosal surfaces do not elicit a strong systemic im mune response but instead induce a transient local immune response tha t is replaced by long-term peripheral unresponsiveness - this is terme d mucosal tolerance. The phenomenon of oral tolerance is well establis hed and considerable attention has focussed on defining the underlying mechanisms. However, only comparatively recently was the induction of tolerance via the respiratory mucosa described, and it is this form o f mucosal tolerance which forms the basis of this review.