A Study of the Intranasal Challenge Assay of Pertussis Vaccine Using Iodine-131

Abstract

The present study was undertaken to determine the cause of the wide variation in the response of mice following intranasal challenge with virulent H. pertussis. Mice, both normal and immunized, were inoculated intranasally with killed H. pertussis organisms labelled with iodine-131. The course of the tagged antigens, in the lungs and other organs of these animals, was followed by radioisotope counting. The lung uptake varied from 31.6% to 77.5% of the challenge dose in immunized animals and from 25.0% to 83.7% in non-immunized animals. It was considered that this variation was large enough to contribute substantially to the wide discrepancies found in animal assays. To date the cultures employed for intranasal challenge have all been of low virulence when administered by this route. A considerably more virulent strain of challenge organism than those in use now would be necessary to overcome the variations in the assay caused by uneven lung uptake of challenge culture. It was also found that the lungs of immunized mice were cleared more rapidly than the lungs of non-immunized mice in the 24-hr. period following the intranasal inoculation.