Immunoprotective activity of ribosomes from Haemophilus influenzae

Immunization with ribosomal preparations from Haemophilus influenzae type b elicited protective immunity in mice. Ribosomes from disrupted cells where isolated by differential centrifugation using sodium dodecyl sulfate. The washed ribosomes contained 25% protein and 75% ribonucleic acid and sedimented as a single peak on sucrose density gradient analysis with a sedimentation coefficient of 67S, using Escherichia coli ribosomes as a 70S marker. Immunodiffusion tests with antipolyribose phosphate serum showed that the ribosomes were free from capsular material. Mice immunized subcutaneously with ribosomes, with or without adjuvant, were challenged intraperitoneally with 100 to 1,000 mean lethal doses of H. influenzae type b suspended in gastric mucin. Significant protection was induced by ribosomes and was compared to that obtained after sublethal infection with live cells. The protection was greatly enhanced after incorporation of ribosomes into adjuvants. Maximum protection (90 to 95%) was observed at 1 to 2 weeks after immunization. Ribosomes from a nonencapsulated strain of H. influenzae were as immunogenic as those from the encapsulated strain, demonstrating that the capsular material is not responsible for immunogenicity of Haemophilus ribosomes.