Characteristics of Complement Fixation by Aggregated IgE

Abstract

Abstract Aggregated IgE fixed late components of complement (C), i.e., C3–C9, through an alternate pathway, bypassing C1, 4, and 2 whereas monomeric IgE did not. The aggregate, however, did not fix purified C3, suggesting that C3 activator system is involved in the reaction. On a weight basis, aggregated Fc had higher C-fixing activity than aggregated IgE, and aggregated F(ab′)2 was less active. The results indicated that structures essential for C fixation are present in the Fc portion of IgE molecules. A mild reduction and alkylation of IgE, which degraded structures involved in passive sensitization of monkey skin, did not affect the C-fixing properties of the protein.