The effect of thymectomy, hemi-thymectomy and sham thymectomy on experimental myasthenia gravis in guinea-pigs.

Experimental thymitis and a partial neuromuscular block was produced in guinea-pigs by immunization with homologous thymus or skeletal muscle tissue in Freund's complete adjuvant. A boosting injection with the specific antigens 3 weeks after the initial immunization did not markedly increase the incidence of thymitis or of partial neuromuscular block. In animals with a partial neuromuscular block, thymectomy was followed by return of the muscle tetanus pattern to normal within 2–3 days. In contrast, the partial neuromuscular block persisted for 4 days after hemi-thymectomy and in some animals for as long as 10 days after sham thymectomy. These findings are in keeping with the hypothesis that experimentally induced thymitis may result in the release of a factor from the thymus which blocks neuromuscular transmission.