Delayed Hypersensitivity to Fungal Antigens in Mice. III. Characterization of the Active Component in Immunogenic RNA Extracts

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Abstract
In a mouse model, cell-mediated immunity to Coccidioides immitis, as assayed by the delayed hypersensitivity skin test, was transferred with whole immunogenic RNA extract and its < 33S and 6S–13S sedimentation fractions. Both fractions were cleaved by RNase, but the products retained their transfer activity. The < 33S fraction of immunogenic RNA extract was inactivated by pronase, whereas the 6S–13S fraction was resistant to the proteolytic enzyme; however, after RNase treatment the latter fraction was sensitive to pronase. This finding suggests a protective role for RNA. Dialysis of immunogenic RNA extract yielded a dialysate with a ratio of absorbance at 260 nm to that at 280 nm (A260:A280) of 1.02. Similarly, the dialysis product of RNase-treated RNA is active and has an A260: A280 ratio of 1.34. The data indicate that at least part of the active moiety of immunogenic RNA extracts is an RNA-associated, pronase-labile peptide or nucleopeptide. Furthermore, it is possible that the dialyzable transfer factor may be the same peptide or nucleopeptide cleaved from immunogenic RNA during preparation of the transfer factor.