The effect of limited fragmentation of porcine 19 S IgM on agglutination and complement fixation. Evidence that at least two intact subunits are required for complement fixation by IgM antibody.antigen complexes.
Limited fragmentation of pig IgM anti-Salmonella with pepsin gave a 12 S product which agglutinated Salmonella almost as efficiently as the original IgM but the complement fixing ability of the complexes was substantially lowered. The 12 S product was shown to consist of molecular entities having intact Fc regions with an average of 3 or 4 intact Fab arms still attached. Our results appeared to show that removal of Fab arms by pepsin was a random process and on this basis a mathematical model was set up. From this model it was possible to calculate the frequencies of molecular entities which would give rise to the observed average of 3 or 4 Fab arms. The most likely explanation of our results is that complexes need to be formed by molecules having at least two intact subunits before efficient complement fixation takes place.
D000818:Animals; D000907:Antibodies, Bacterial; D000936:Antigen-Antibody Complex; D001666:Binding Sites, Antibody; D003165:Complement System Proteins / Q000378:metabolism*; D007128:Immunoglobulin Fragments; D007075:Immunoglobulin M; D008970:Molecular Weight; D012475:Salmonella / Q000276:immunology; D013329:Structure-Activity Relationship; D013552:Swine
D000907:Antibodies, Bacterial; D000936:Antigen-Antibody Complex; D007128:Immunoglobulin Fragments; D007075:Immunoglobulin M; D003165:Complement System Proteins