Informative value of a mouse model ofKlebsiella pneumoniae infection used as a host-resistance assay

To obtain a host-resistance assay (HRA) for quantitative evaluation of immunostimulatory effects of various substances, an experimental model ofK. pneumoniae inhalatory infection was elaborated. The highly virulent bacterial strain (inhalation LD₅₀=400 CFU), appliedvia the natural route into the respiratory tract elicits an acute infectious process possessing characteristic dynamics. Although the intensity of clearance in the bronchoalveolar lavage after challenge or the mean survival time can be used in individual cases for quantitative resistance determination, the inhalation LD₅₀ values yielded the most standard results. Systemic immunization with the corpuscularK. pneumoniae vaccine provided a high protection expressed by increasing the inhalation LD₅₀ by two orders of magnitude. The antibodies formed, detectable by the ELISA test, are specific for capsular polysaccharide. The type-specific immunity was also found in the protection test. The nonspecific stimulatory effect of the peptidopolysaccharide complex isolated fromListeria monocytogenes (EiF) was manifested at the level of one LD₅₀ only while with higher infectious doses it was absent. However, the adjuvant activity of EiF was significant. The HRA can distinguish and quantitatively determine both nonspecific and specific stimulatory effects of immunomodulatory substances. Translated by I. Miler