Immunoglobulins in myasthenia gravis. Kinetic properties of the acetylcholine-receptor antibody studied during lymph drainage.

A specific immunoglobulin, the receptor antibody, can be found in most patients with myasthenia gravis. In order to study the kinetic properties of this antibody, serial determinations of receptor antibody, total IgG and IgG 3 were made during drainage of thoracic duct lymph in three patients. The values obtained were used in a mathematical model to calculate some kinetic parameters. Values for T 1/2 and fractional rates of synthesis and catabolism obtained for total IgG and IgG 3 by this method were shown to agree with those found with other techniques. Most of the receptor antibody activity was found in the IgG 3 fraction but the receptor antibody had a shorter T 1/2 and higher fractional rates of synthesis and catabolism than IgG 3. These kinetic characteristics are consistent with rapid variations in plasma concentration of the receptor antibody. The cause of this rapid turnover could be strong antigenic stimuli and rapid elimination by the antigen, the cholinergic receptor protein.