The existence of a protective local immune system that seemed to function independently of systemic immunity, was initially proposed by Besredka (1919); he observed that rabbits, after oral immunization with killed Shiga bacillus, were protected against fatal dysentery irrespective of the serum antibody titer. Davies (1922) obtained evidence in soldiers stationed around Jerusalem, to suggest for the first time the presence of local immunity in humans; his observations indicated that bacterial agglutinins could appear in dysentery stools several days earlier than in the blood. The molecular basis for local immunity was established when Tomasi et al. (1965) confirmed that external secretions contained a unique immunoglobulin (Ig) subsequently called secretory IgA (SIgA).