Biological properties of an immunogenic pneumococcal subcellular preparation

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Abstract
A subcellular fraction, designated PSP-3R, prepared from rough, type 3R Streptococcus pneumoniae is described, which affords excellent protection to mice against challenge with smooth organisms of the homologous serotype 3S and significant protection against heterologous challenge with serotypes 1S and 2S. Adjuvant enhances the protective capacity of the vaccine but is not necessary for immunogenicity. Protection induced by PSP-3R can be passively transferred tp normal mice with serum from actively immunized animals. The protective capacity can be completely absorbed out with rough or smooth type 3 organisms but not with rough type 1R or 2R cells. PSP-3R immune serum was tested in a passive hemagglutination assay against type 3 capsular polysaccharide-coated erythrocytes and found to have no detectable anticapsular antibody. The possible identity of the immunogen (s) in the vaccine is discussed.