Experimental myasthenia in mice. The role of the thymus and lymphoid cells.

A possible function of the thymus gland with regard to developing neuromuscular block after immunization with thymus extract is discussed. Inbred female C57BL/6 mice were immunized with thymus extract from female C57BL/6 (syngeneic), male C57BL/6 mice, AKR mice (allogeneic) and guinea-pigs and calves (xenogeneic). Two weeks later, the waning phenomenon was observed from the electromyography (EMG) in xenogeneically, allogeneically and syngeneically immunized mice. The waning reverted to a normal pattern following an intraperitoneal injection of neostigmine methylsulphate. EMG tracings revealed a decrease in the incidence of the waning phenomenon in those mice which were immunized after adult thymectomy. The passive transfer of the waning phenomenon to non-thymectomized recipients could be achieved by the intravenous administration of lymph node cells obtained from the mice that had developed a myasthenic neuromuscular block after immunization. This finding was also observed in the recipients when the donors of lymph node cells had not developed the block. On the other hand, administration of sera from mice with the waning phenomenon after immunization resulted in a neuromuscular block in both normal and adult-thymectomized mice. However, sera obtained from mice without waning did not have this feature.