AN EVALUATION OF SHIGELLA VACCINES BY HEMAGGLUTINATION ON HUMAN SERA FROM VACCINATED VOLUNTEERS

Abstract

The bacterial agglutination test has been conventionally employed for the titration of humoral antibodies for Shigella in human sera. In the field trials and also in the small scale trials for evaluating the prophylactic powers of Shigella vaccines, the determination of the degree of increase in bacterial agglutinins following vaccination has been considered as one of the important criteria as well as the survey of the morbidity rates among vaccinated population (Cooper and Keller, 1948; Ando et al., 1958) . By means of bacterial agglutination test, it is, however, generally impossible to detect the antibodies for Shigella sonnei in sera from the human subjects immunized with Shigella vaccines or from bacillary dysentery patients if any, whereas it is possible for Shigella flexneri to a considerable extent (Cooper and Keller, 1948; Cooper et al., 1948, 1949a, 1949b; Takigami and Tadokoro, 1953; Ando et al., 1958) . It has, therefore, been difficult to evaluate the vaccine prepared from Shigella sonnei by the conventional bacterial agglutination test.
On the other hand, it was established by many workers that bacterial hemagglutination test is generally more sensitive than the bacterial agglutination test (Neter, 1956) . In the case of Shigella, Neter and Gorzynski (1954) and Neter and Walker (1954) established the method to determine the agglutinin titers for Shigella by the bacterial hemagglutination test. They carried out with success the surveys of the distribution of hemagglutinin titers for Shigella among some population, using as antigens the erythrocytes modified with soluble antigenic components liberated in the supernatant from bacterial suspensions heated at 100°C for 1 hour. Chun and Park (1956) and Chun et al. (1957) reported the studies on the hemagglutination reactions of the rabbit antisera immunized with Shigella flexneri, by employing the tannic acid-treated erythrocytes sensitized with acidextracted antigens as well as the erythrocytes sensitized according to Neter and Gorzynski (1954) or Neter and Walker (1954) . Nakaya (1957) studied the relationships among the bacterial agglutinins, the hemagglutinins, and the passive mouse-protective powers of human and rabbit antisera for Shigella, resulting in that the highest sensitivity could be obtained by the hemagglutination test for determination of antibody titers.
In the present experiments, titrations of agglutinins were performed on sera from volunteers immunized with Shigella vaccines and from dysentery patients, by employing the method of hemagglutination test described by the Gastroenteritis Studies Group of the Bacteriology Department at Walter Reed Army Institute of Research (Young, 1959) . The present study aimed at the evaluation of the prophylactic powers of Shigella vaccines prepared by chrome alum treatment,
with respect to their immunogenicity to human subjects.
This has been accomplished by comparing the hemagglutinin titers of sera from vaccinated individuals with those from individuals recently convalescent from bacillary dysentery. In addition to this, sensitivity and specificity of hemagglutination have been compared with those of bacterial agglutination by using sera from vaccinated human subjects and hyper-immune rabbit sera. It will be presented that the hemagglutination test was very satisfactory at any respect in determination of agglutinin titers for Shigella, particularly in the case for Shigella sonnei.