Experimental myasthenia gravis, myositis and myocarditis in guinea-pigs immunized with subcellular fractions of calf thymus or calf skeletal muscle in Freund's complete adjuvant.

Experimental thymitis and a partial neuromuscular block was produced in guinea-pigs by immunization with the subcellular fractions of calf thymus and skeletal muscle homogenates. A significant incidence of thymitis was observed in guinea-pigs immunized with the soluble or with the microsomal fractions of thymus or of skeletal muscle. The mitochondrial fraction of thymus or skeletal muscle was less effective in producing thymitis. In guinea-pigs immunized with the subcellular fractions of skeletal muscle additional evidence of experimental myositis (60%) and myocarditis (40%) was shown. All three skeletal muscle fractions were equally effective in the production of experimental muscle lesions. A close correlation was found between the presence of thymitis and the evidence of a partial neuromuscular block. In contrast, a partial neuromuscular block was not observed in animals with experimental myositis but without thymitis. This finding gives further support to the hypothesis that the inflamed thymus is a source of a factor which blocks neuromuscular transmission in experimental myasthenia gravis.