Immunogenicity of Ribosomal Preparations from Yeast Cells of <i>Histoplasma capsulatum</i>

Abstract

Protective immunity was elicited by immunization of mice with ribosomal preparations from yeast cells of Histoplasma capsulatum . Ribosomes from disrupted cells were isolated by differential centrifugation using sodium dodecyl sulfate. These preparations contained 55% protein and 45% ribonucleic acid and sedimented as a single peak with a sedimentation coefficient of 77 S on sucrose density gradient analysis. Mice immunized subcutaneously with ribosomes, with or without adjuvant, were challenged intravenously with 8 × 10 6 yeast cells of H. capsulatum . Significant protection was induced by ribosomes and was greatly enhanced by adjuvants. Protection measured by 30-day survival compared favorably with the immunoprotection assessed by absence of lung lesions and negative spleen cultures. Treatment of ribosomes with ribonuclease before immunization reduced protection by 85%, whereas trypsin and Pronase reduced the protection by 50 to 55%. These findings indicate that both intact ribosomal ribonucleic acid and protein are necessary for maximal immunogenicity of Histoplasma ribosomes.