A transient monoclonal human IgG1 kappa protein with anti-thyroglobulin activity: lack of cross-idiotypy with polyclonal anti-thyroglobulin antibodies.

A female patient in her early sixties had for a period of at least 4 months a monoclonal IgG1 kappa protein in her serum and at the same time a very high level of anti-thyroglobulin antibodies. Different isolation procedures showed that the M component was responsible for the high anti-thyroglobulin activity. Anti-idiotypic antibodies raised in a rabbit against the monoclonal protein inhibited the M component's anti-thyroglobulin activity, and purified thyroglobulin blocked the reaction between the M component and the anti-idiotypic antiserum. After the M component had disappeared, no cross-idiotypic immunoglobulins could be detected in the patient's serum, nor could the anti-idiotypic antiserum inhibit the residual anti-thyroglobulin activity present in the serum at this time. No reaction could be detected between the antiserum and the anti-thyroglobulin antibodies of sera of other patients. Idiotypic autoantibodies against the M component, which might have caused its disappearance, could not be demonstrated.