Cross-Immunization

CROSS-IMMUNIZATION, a method of immunization aimed at elucidating the immunobiological relationships of two or more microbes. If cross-immunization is performed with microbes A and B, one group of animals is immunized with a culture of microbe A, and another group with a culture of microbe B. Note: The OCR text contains a garbled intrusion regarding genetic crossing-over and chromosome interference which belongs to a different article. Ignoring the garbled fragment, the method proceeds as follows: upon completion of immunization, the animals immunized with microbe A are tested for the acquired immunity by administering a lethal dose of microbe B, and conversely, the animals immunized with microbe B receive a culture of microbe A. In addition to testing immunity, cross-immunization may also pursue the goal of determining in immunized animals the state of antibodies to the antigens participating in the experiment, i.e., studying antigenic properties. Consequently, upon completion of immunization, agglutination, complement fixation, and other tests are performed using sera from animals of group A and microbe B, and vice versa. The agglutination reaction and other immune reactions with the specific microbe (A) are also set up using the serum of group A animals, and the titer is compared with the titer of reactions with microbe B. With the serum of group B animals, immune reactions are likewise set up with microbe B. From the difference in titers, conclusions can be drawn about the degree of closeness of the studied microbes to each other. Example: 10 rabbits are immunized with the typhoid bacillus at weekly intervals. Fourteen to fifteen days after the completion of immunization, they are injected with 1-1.5 lethal doses of a culture of some parastrain being tested for its relationship to the typhoid bacillus. If the rabbits remain alive, it can be concluded that the typhoid bacillus confers immunity against the tested strain (parastrain) as well. Simultaneously, the agglutination reaction and other immune reactions are set up using the serum of the immunized rabbits and typhoid bacilli on the one hand, and the tested strain on the other. In a parallel series of experiments, 10 rabbits are taken and immunized with the tested strain to study its relationship to typhoid fever. Upon completion of immunization, a comparative study of immunity against the typhoid bacillus and the tested strain is performed.