Immunologic studies of anthrax. IV. Evaluation of the immunogenicity of three components of anthrax toxin.

Three components of anthrax toxin (edema factor, protective antigen, and lethal factor) were separated and tested singly at three dose levels and in factorial combination (27 treatments) to determine their efficacy ao immunogens in a resistant host (rat) and in a susceptible host (gulnea pig). The efficacy of each component used as an immunogen was determined by its ability to (i) protect against the establishment of the disease, (ii) influence the number of bacilli-ml of blood at death, (iti) chlnge the units of toxin/ml of blood at death, (iv) affect the antibody titer (Ouchterlony), and (v) alter the units of toxin neutralizad/iml of blood. Lethal factor was the only immunogenic component against both B. anthracis spore and toxin challenge in each of the hosts tested. Protective antigen was protective in the guinea pig as both a primary and interactive response. In both animals the edema factor was nonimmunogenic by the methods of evaluation and gave poor protection against both the spore and toxin challenge; however, certain interactions were noted. The interaction of antibody and the i",'' Jefense mechanisms in resistant and susceptible hosts are discussed.