A Purified Complement-fixing Antigen from Mycobacterium johnei

THE antigen most commonly used in complement fixation tests for Johne's disease is a suspension of the specific organism, Mycobacterium johnei . This form of antigen is not entirely satisfactory for two reasons. Like many other particulate antigens it tends to fix complement non-specifically in the presence of cattle sera in which the proteins, particularly the globulins, have become unstable during delay in shipment. In the second place, marked cross-fixation occurs with sera of cattle sensitized to avian tubercle bacilli, because Johne's bacilli contain components common to acid-fast bacteria. Attempts have been made therefore to improve the Johne's bacillus antigen by various methods of fractionation and purification. The present communication describes the method which has proved the most satisfactory to date.