A Bioassay for Estimation of Pneumococcal Polysaccharide in Unresponsive (Paralyzed) Mice

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Abstract
Summary and Conclusions: A bioassay is described for estimating the amount of pneumococcal polysaccharide present in intact mice and capable of binding antibody. The method is based upon measurement of the amount of antibody required to passively protect mice from pneumococcal challenge. The half-life of immunologically titratable SII was found to be 5 days for the first 10 days after administration and 50 days from 11 to 70 days after administration, and to be independent of the dose of antigen injected (5 to 100 µg). Approximately 0.8 µg of a rabbit anti-type II pneumococcal polysaccharide given intravenously will protect 50% of mice from pneumococcal challenge 24 hr later. Mice, 10 days after immunization with 0.05 µg of SII, had approximately 13 µg of specific antibody available for binding with administered SII as measured by the decrease in the amount of passively administered antibody required to protect them from pneumococcal challenge. The results are supportive of the hypothesis that immunologic paralysis is the result of a block in antibody synthesis rather than of the combining of antibody formed with excess antigen present.