Studies in immunization by a species antigen: I. The presence of ‘species antigen’ and of ‘opposition factor’ in bacteria other than pneumococci

Abstract

The experiments here described proved that preparations made from widely different classes of bacteria are capable of inducing immunity in mice against pneumococci. The success of these preparations was found to depend on the differential separation of an active immunizing antigen from another bacterial constituent—an ‘opposition factor’—which interferes with immunization. Further investigation and comparison depend largely on the discovery of a really effective method for the isolation and purification of the active antigen. Until its chemical nature is determined, the identity of the pneumococcal species antigen with similarly acting substances found in other bacteria remains unproved.Pathogenic bacteria depend for their virulence and invasiveness on certain products individual to the species or type, and specific immunity is due to the development of the appropriate antibodies. But chemotherapy, as in the case of the sulphonamides, interferes with a less specialized metabolic process of the microbes and is neither species nor type specific in action. It is reasonable to infer that bacteria may possess in common a vital process associated with the presence of a common constituent which may be antigenic. ‘Species antigen’ may be a substance of this nature.In view of the wide distribution of ‘species antigen’ among bacteria generally, it is probable that this constituent has already been separated and named in accordance with its presence in a particular species, but irrespective of its potential immunizing capacity.So far as pneumococci are concerned, there is good evidence that species antigen may be identical with the species C carbohydrate. Tillett (1927) found that rabbits injected with successive courses of heat-killed pneumococci, whether of types I, II, III or of avirulent rough strains, developed an equal increase of resistance to infection by type III Pneumococcus. In 1936 Enders, Wu & Shaffer varied the procedure, and by injections of rough pneumococci prepared an antiserum which gave passive protection to rabbits against infection by type III Pneumococcus. This antiserum lost its protective power after absorption with the species C carbohydrate.