Immunologic Studies on New Preparation of Type-Specific Polysaccharide from Pneumococcus Type I

The isolation of chemically different polysaccharides by Heidel-berger and Avery 1 from various types of pneumococci places the problem of type-specificity in immunologic reactions on a definite chemical basis. Since the polysaccharide from Type I pneumococcus, called the “Soluble Specific Substance,” was not antigenic, it can only be considered as a hapten of the pneumococcal antigen. Later Wadsworth, 2 Enders, 3 and others obtained preparations of polysaccharide from pneumococcus Type I, which were antigenic in mice. Therefore they were believed to be different from the soluble specific substance.

Recently Avery and Goebel, 4 by omitting the alkaline treatment, isolated an acetyl polysaccharide from the autolyzed broth-culture of pneumococcus Type I. Like similar preparations from other laboratories, the acetyl polysaccharide was antigenic in mice. However, the antigenicity was destroyed by treatment with alkali with accompanying loss of acetyl groups. Thus it is probable that Enders and Wadsworth's polysaccharides may be identical with the acetyl-polysaccharide. Enders and his colleagues 5 have already confirmed the observations of Avery and Goebel.

By using a method which minimized hydrolysis by acid or alkali in the preparation of polysaccharide, we have obtained a product even more complete than the acetyl polysaccharide. An autolyzed broth-culture was not autoclaved, as in Avery and Goebel's procedure, but was concentrated at a reduced pressure so that the temperature was never higher than 37°C. After the subsequent purification according to Avery and Goebel's method 4 a white polysaccharide was obtained. This polysaccharide reacted with a homologous immune-rabbit serum, previously absorbed with the acetyl polysaccharide. On the other hand, the acetyl polysaccharide did not react with its homologous immune-rabbit serum absorbed by the new polysaccharide (Table I). A quantitative precipitin-titration showed that the new polysaccharide precipitated almost 3 times more antibody-protein than did the acetyl polysaccharide.

Although an antipneumococcal serum absorbed with our polysaccharide was still agglutinative and specifically protected mice from an otherwise fatal dose of pneumococci (Type I), the titre was greatly reduced.

The new polysaccharide in small doses produced active immunity in mice. Rats given intravenous injections of the polysaccharide-solution produced sera which protected mice from a fatal dose.

When the polysaccharide solution was heated at 100°C. in 0.05 N NaOH or 0.5 N acetic acid, the hydrolytic product still produced active immunity in mice, but failed to precipitate the immune serum absorbed with the acetyl polysaccharide.