Antiacetylcholine receptor antibody (anti-AChR) was spontaneously synthesized by cultured thymic tissue from 19 of 35 patients with myasthenia gravis. Two other thymus cultures produced antibody after stimulation by pokeweed mitogen. Antibody production correlated with histologic evidence of thymitis, long duration of symptoms, or high serum anti-AChR values. None of seven thymomas synthesized antibody in culture, but evidence suggested that there had been in vivo synthesis or trapping of anti-AChR.

Clinical improvement after thymectomy, during the short period of study, did not correlate with synthesis rates of anti-AChR production by the removed thymus. The rates of anti-AChR production in culture were too low to suggest that the thymus is the major source of this antibody. Although we did not find a clear relationship between anti-AChR antibody and clinical state within 3 months of thymectomy, in a study of 25 nonimmunosuppressed, nonthymoma patients followed for 1 to 4 years, we found a significant correlation (p <0.05, Spearman Rank correlation) between fall in anti-AChR antibody and clinical improvement after thymectomy (unpublished observations).