A chemical study of tuberculin.

Some time ago in the course of a study of the tuberculin and allied reactions, Zinsser 1 showed that extracts of powdered tubercle bacilli, rendered as free as possible from protein, by acid precipitation and boiling, contained substances precipitable by alcohol, which substance produced skin reactions of the delayed type, in tuberculous guinea pigs. The acetic acid precipitate gave a similar reaction, which was not lost on repeated solution in alkali and reprecipitation with acid. Several possibilities of the relationship between the protein precipitate and the so-called “residue antigen,” from which the protein had been removed, were discussed and the question was left open for further work.

The investigation of the residue was continued by Zinsser and Parker, 2 who extended the observations to other bacteria, and found that in the case of each one tried, including staphylococci, pneumocci and meningococci, a similar preparation could be obtained. In the case of these organisms, however, the products were tested by the precipitin reactions, since chronic infections of a type suitable to produce skin hypersensitiveness could not readily be produced in guinea pigs. In all cases these bacterial residues reacted specifically with immune sera by the precipitin test.

It was shown that these preparations were made up largely of non-nitrogenous material, which gave the Molisch test for carbohydrates. Heidelberger and Avery 3 have shown that substances prepared from Pneumococcus I1 and I11 broth cultures, and which are undoubtedly identical with the active material of the residue antigen, are complex carbohydrates or gums. The writer has'come to the same conclusion in the study of a specifically precipitable material prepared from bread yeast. The similarity of results from such unrelated types of microorganisms indicates that the production by bacteria of specific gums, reacting with immune sera by the precipitin test, may be a general phenomenon. It should be noted that these substances, while reacting with immune sera, are apparently incapable of themselves inducing antibody formation, and hence are not antigens in the strict sense.