The effect of azathioprine on gammaglobulin synthesis in man.

The effect of azathioprine therapy on gammaglobulin synthesis was evaluated in nine patients with rheumatic disorders. The rates of synthesis of IgG and IgM were calculated before and after 4 months of azathioprine treatment using turnover studies of radioiodinated gammaglobulins. The synthesis of IgG decreased 33.4% of the initial IgG synthetic rate. Seven of nine patients showed reductions of IgG synthesis ranging from 16.8 to 74.1%. IgM production decreased from 24.5 to 74.2% in eight of nine patients with a mean reduction of 40.9%. Studies before and after a control period of 4 months of placebo in six patients revealed a mean increase in IgG and IgM synthesis. Serum immunoglobulin concentrations after 4 months of azathioprine treatment were not consistently reduced and did not parallel changes in immunoglobulin synthesis. Reduced gammaglobulin synthesis may play a role in the therapeutic action of this and other "immunosuppressive" drugs.