A study of sensitivity to Hemophilus pertussis in laboratory animals; the formation of antibodies and the development of sensitivity in laboratory animals injected with Hemophilus pertussis antigens.

The antigenic response of laboratory animals to injections of Hemophilus pertu8sis exotoxin, vaccine, and nucleoprotein (NPD)L was measured. For this purpose we prepared hyperimmune sera in rabbits against each of these antigens. Antitoxic serum was prepared by repeated injections into rabbits over a long period of time of filtrates of H. pertussis culture detoxified with formalin. During such a series of injections the rabbits develop antibodies that neutralize the toxic principle of H. pertussis filtrate. This toxin, it should be mentioned, is very unstable and of low titer. Owing to the fact that the filtrates of H. pertussis culture contain an abundance of somatic antigens, the serum of rabbits immunized with culture filtrates contains, in addition to antitoxin, high titers of precipitins, agglutinins, and other antibacterial antibodies. However, the integrity of H. pertussis toxin as an antigen is supported by the fact that antibacterial serum prepared by immunization of rabbits with H. pertussis vaccine does not contain an appreciable amount of antitoxic antibodies. The origin of the toxic principle in filtrates of H. pertussis culture is not clear. Strean and Grant (1940) extracted toxin from the bodies of H. pertussis organisms (endotoxin) and prepared immune serum against it in rabbits. Evans (1940) found that this antitoxin neutralized pertussis, parapertussis, and bronchiseptica toxins without differentiation. We were concerned only with the different effects observed following the injection of toxin-antitoxin mixtures into normal and sensitized mice. H. pertussis toxin, 0.1 ml, containing 2 MLD (as determined for normal mice) was incubated for 1 hour at room temperature with different amounts of antitoxin. The mixture in a volume of 0.2 ml was injected intravenously into both normal and sensitized mice. The results of some of our experiments are given in table 1. The amounts of antitoxin used in the mixtures, with the exception of the last one, were sufficient to make these injections harmless for normal mice. In contrast to this, we observed a high incidence of deaths in sensitized mice even after the injection of a mixture containing a large dose of antitoxin. As stated before, in these experiments we used toxin containing 2 MLD, the volume of toxin being not more than 0.1 ml. This volume of toxin did not