Studies into the occurrence of soluble antigen-antibody complexes in disease. II. Criteria for distinguishing soluble complexes from other macromolecular histamine releasers.

We have defined criteria for distinguishing several macromolecular histamine releasers derived from serum. The agents characterized were aggregated γ-globulin (AGG), soluble antigen–antibody complexes (SC), antibody to γ-globulin (anti-CII) and anaphylatoxin. The criteria used included the solubility of these materials in ammonium sulphate, their behaviour on Sephadex G-200 both at pH 8·0 and at pH 3·0, their action on the guinea-pig ileum and the influence of both reduction and alkylation and of γ-globulin on their histamine-releasing activity. It was found that AGG differed from SC in being excluded from Sephadex G-200 at pH 3·0. Anti-CII could be distinguished from AGG and SC since it was partially and irreversibly inhibited by γ-globulin and was eluted in the Sephadex middle fraction at pH 8·0. Anaphylatoxin differed from AGG, SC and anti-CII in showing no inhibition by γ-globulin, in being partially soluble in 50% ammonium sulphate, in being labile on Sephadex G-200 and in producing a contraction of the guinea-pig ileum. These criteria provided a basis for identifying unknown macromolecular histamine releasers found in serum.