Immunologic memory to phosphorylcholine III. IgM includes a fine specificity population distinct from TEPC 15

Area of Science:

• Immunology
• Molecular Biology
• Genetics

Background:

• The origin of antibody diversity is crucial for adaptive immunity.
• Somatic mutation and germ-line gene rearrangement are key mechanisms.
• The role of class switch recombination in somatic mutation is debated.

Purpose of the Study:

• To investigate the origin of distinct antibody variable regions (Group I and Group II) in the PC-KLH memory response.
• To test the hypothesis that Group II antibodies arise from somatic mutation activated by class switching from IgM to IgG or IgA.

Main Methods:

• Antibody separation using affinity chromatography (PC-Sepharose).
• Characterization of fine specificity and idiotype using ELISA.
• Detection of IgM components in purified antibody populations.

Main Results:

• Group I antibodies were T15 idiotype-positive and inhibited by PC and NPPC.
• Group II antibodies were T15 idiotype-negative, inhibited mainly by NPPC, and contained a significant IgM component.
• High levels of Group II IgM were detected during the early secondary response.

Conclusions:

• The presence of Group II IgM antibodies contradicts the hypothesis of somatic mutation occurring post-class switching.
• Results strongly suggest that Group I and Group II antibodies originate from distinct germ-line genes (V, D, or J).
• Alternatively, if somatic mutation occurs, it must precede class switching for Group II antibody generation.