Immunologic protection against the Legionnaires' disease bacterium in the AKR/J mouse

Female AKR/J mice were challenged with the Washington strain of Legionnaires' disease (LD) bacteria. Nonimmunized mice inoculate intraperitoneally with 2 x 10(8) colony forming units became ill within 4 h and died within 24 h. Progressive histopathologic changes initiated as early as 2 h after inoculation involved the lymphoid organs, the crypts of the small intestine, and the liver. Necrosis with minimal inflammatory cell reaction was the primary lesion. Immunization with a soluble LD bacterial antigen failed to prevent illness but protected against death and development of abnormal histologic changes.