THE ACTION OF SOLUBLE ANTIGEN--ANTIBODY COMPLEXES IN PERFUSED GUINEA-PIG LUNG.

When soluble antigen—antibody complexes, prepared in antigen excess, were injected into the perfused pulmonary artery of the unsensitized guinea-pig lung, they produced a bronchoconstrictor response which was associated with the appearance of histamine and a slow-reacting substance in the effluent. This activity was inhibited by the presence of normal rabbit serum or rabbit globulin; rabbit albumin and bovine γ-globulin produced no inhibition. Insoluble antigen—antibody complexes prepared at equivalence were at least 125 times less active than soluble complexes prepared in antigen excess. On comparing the activity of different solutions of soluble complex prepared in antigen excess ranging from 2½ to 160 times that required for equivalence, all were found to be equal. The properties of soluble antigen—antibody complexes are consistent with the possibility that circulating antibody may participate in in vivo anaphylaxis, if reached by an amount of antigen greater than that required for equivalence.