IgG subclass distributions in anti‐hapten and anti‐polysaccharide antibodies induced by haptenated polysaccharides

Mice were immunized with hapten [NIP, (4-hydroxy-5-iodo-3-nitrophenyl)acetyl or TNP (2,4,6-trinitrophenyl)] conjugates of Ficoll or pneumococcal polysaccharide type 14 (S14), and they were bled on days 10 or 14. Anti-hapten and anti-polysaccharide antibodies were determined from the sera or from fractions (IgM + IgA). IgG1, IgG2a, IgG3 or IgG2b separated by a gradual acid elution from protein A. Approximately one-half of both anti-hapten and anti-polysaccharide antibodies was found in the IgM + IgA fraction. The subclass distribution of the IgG antibodies was dependent on the antigenic determinants. Polysaccharide antibodies were mostly in the IgG3 fraction (36-62%) and in the IgG1 fraction (18-36%). Hapten IgG antibodies were mostly in the IgG1 fraction (38-74%): each of the other three subclasses contributed the average of 13%. These results provide the first evidence that antibodies to different determinants of one antigen have grossly different isotype distributions.