Experimental myositis in rats. I. Histological and creatine phosphokinase changes, and passive transfer to normal syngeneic rats.

An allergic myositis was produced in an inbred strain of rats by giving repeated injections of heterologous muscle with complete Freund's adjuvant. Histological lesions developed after two or more injections. The activity in the serum of the enzyme creatine phosphokinase (CPK) was found to be elevated after two injections and reached maximum levels after three to six injections. Transfer of lymphoid cells from spleen, lymph node or thoracic duct, after five immunizing injections resulted in the development of lesions in syngeneic recipients 5–10 days later. The lesions were milder than in the donors, but did result in elevation of the serum CPK activity in the recipients. It is concluded that measurement of the serum CPK activity is a convenient and objective reflection of the histological lesions produced in experimental allergic myositis.