Measurement of antibody-producing capacity in man. V. Immunoglobulin classes of antibodies to flagellin.

The immunoglobulin classes of antibody to flagellin were determined in twenty-eight persons injected with flagellin from . Sera were examined from non-immunized persons and from persons given primary and secondary immunization. Results obtained by titration before and after treatment of whole serum with 2-mercaptoethanol (ME) were compared with those obtained after fractionation of serum by gel filtration on Sephadex G-200 and by radio-immunoelectrophoresis (RIEP). The ME procedure, whilst not fully reliable for determining class of specific antibody in individual sera, is suitable for routine analyses of many sera. After gel filtration, ME-sensitive antibodies were mostly contained in the IgM protein peak whereas ME-resistant antibodies were mainly associated with the IgG protein peak. Using RIEP, specific antigen binding to the IgM, IgG and IgA precipitin lines was demonstrated. Binding of flagellin to the IgM precipitin line correlated with the presence in whole serum of ME-sensitive antibody and binding to the IgG line with ME-resistant antibody. Antigen binding to the IgA line did not correlate with results from ME-sensitivity studies using whole sera. Natural antibody in serum before immunization was entirely IgM. The antibody after primary immunization was mainly IgM but varying amounts of IgG were also produced; a change to the synthesis of entirely IgG antibody during the primary response was rare. The antibody after secondary immunization was mostly IgG; there was no evidence of increased IgM synthesis. IgA antibodies to flagellin were detected during both primary and secondary responses in about half of the subjects tested, but were not quantified.