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The sensitivity and specificity of various antigenic fractions prepared from cell wall, cytoplasm and culture filtrate of Mycobacterium tuberculosis H_37R_a strain was studied by both complement fixation test and agar-gel diffusion test, using homologous and heterologous antisera. The resultsare summarized as follows ; 1. In the complement fixation test with homologous antiserum, the cytoplasmic TCA precipitate antigen possessed the highest titer of 1:512, both the cell wall tween 80 extract antigen and cell wall PBS extract antigen were 1:64, and the culture filtrate PPD and cytoplasmic acetone precipitate antigen 1:32, respectively. 2. The complement-fixing antibody titers obtained with 1 unit of each antigenic fractions against homologous antiserum were as follows ; the cell wall PBS extract antigen; 1:2,560, the antigens of cell wall tween 80 extract, cytoplasmic TCA precipitate and cytoplasmic alcohol precipitate; 1:1,280, culture filtrate PPD antigen; 1:160, and cytoplasmic acetone precipitate antigen; 1:40, respectively. 3. The differential specificity of various antigenic fractions was determined by the numbers of heterologous antisera that showed over 4-fold difference in the complement-fixing antibody titers than that of homologous antiserum. The cell wall PBS extract antigen exhibited such differences with 6 of 7 heterologous antisera and this represented the highest differential specificity, the cytoplasmic alcohol precipitate antigen ; 5, cytoplasmic TCA precipitate antigen : 4, cell wall tween 80 extract antigen; 3, and culture filtrate PPD ; 2, respectively. The cytoplasmic acetone precipitate antigen had none of such a differential specity. 4. The agar-gel diffusion test with homologous antiserum established that the precipitinogenicity of cytoplasmic acetone precipitate was superior to those of both cytoplasmic TCA precipitate and culture filtrate TCA precipitate (PPD). The gighest dilutions of each antigen which showed a precipitation reaction were as follows ; cytoplasmic acetone precipitate was 1:32 and cytoplasmic TCA precipite and culture filtrate PPD were 1:16. The rest of antigenic fractions failed to show precipitation reaction in this system. However, a serum obtained from bovine tuberculosis showed precipitation reaction only with cytoplasmic acetone precipitate antigen, but not with other antigens. The results of this study indicated that the cell wall PBS extract antigen of M. tuberculosis H_37F_a strain was superior to other antigens tested for a complement fixation test in regards of both the sensitivity and the specificity, and that the cytoplasmic acetone precipitate antigen was an effective precipitinogen in the agar-gel diffusion test.
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