Immunological relationships of cell constituents of pneumococcus

In the preceding communication, it has been pointed out that the so-called soluble specific substance of pneumococcus is nonprotein in nature, and in its present state of purification is either itself a polysaccharide, or intimately associated with the carbohydrate. Although antigenically this substance appears capable of stimulating little or no antibody response, serologically it is highly reactive and exhibits to an extraordinary degree the reactions of type specificity in antibacterial serum of the homologous type of pneumococcus. On the other hand it is possible to recover from the pneumococcus cell another substance which is protein in character and which is distinctive in its serological behavior from the soluble specific substance. From bile solutions of pneumococci dilute acetic acid precipitates a protein fraction. This precipitate is washed in water and redissolved in dilute alkali. After repeated precipitations and thorough washing the dissolved material is passed through a Berkefeld filter and reprecipitated. The final precipitate is washed rapidly with acetone and ether and dried in vacuo. The preparation so obtained is a whitish powder, readily soluble in faintly alkaline solution, possessing the properties of a mixture of nucleoprotein and mucoid. It contains about 16 per cent. of nitrogen and 0.5 per cent. phosphorus.

Solutions of nucleoprotein prepared from one type of pneumococcus (Type 11) react in about equal degree with all three types of antipneumococcus serum, and not with antityphoid or normal horse serum. This fact, if confirmed by subsequent investigation of the protein from pneumococci of other types, would indicate, on the basis of specific precipitin reactions, that all pneumococci possess in part at least a common specific protein. The protein of pneumococcus, as contrasted with the non-protein fraction or soluble specific substance is not type specific, but reacts with antipneumococcus serum regardless of type derivation. It is therefore species specific, not type specific.