Protection against pneumococcal infection by a ribosomal preparation.

A subcellular extract prepared from nonencapsulated Diplococcus pneumoniae type 3 protected mice against a subsequent challenge with virulent D. pneumoniae types 1, 2, 3, and 7. Potency ratios ranged from 25 (type 3) to >1,175 (type 1). The immunity induced in mice by this preparation was best obtained by intraperitoneal inoculation followed by intravenous challenge. Mice immunized in this manner were protected up to 12 weeks and could withstand a challenge of several hundred LD(50). The protection was destroyed by treatment of the preparation with ribonuclease and was decreased by treatment with protease. The preparation consisted of 60.5% ribonucleic acid, 29.1% protein, 6.3% deoxyribonucleic acid, and 4.0% hexose. Ultracentrifugation studies indicated that this extract had five constituents which are compatible with ribosomal material.