Extent of specific to nonspecific resistance in mice: parenteral versus aerosol challenge

Quantitative data were gathered concerning the extent of resistance induced in mice immunized by specific and nonspecific means and subsequently challenged both parenterally and by aerosol. Animals were immunized specifically by subcutaneous or intraperitoneal injection of Formalin-killed Klebsiella pneumoniae type I, which was also employed as a challenge organism. The intraperitoneal ld(50) was 30 bacilli. Nonspecific resistance was induced by injection of a Boivin preparation of Salmonella typhimurium endotoxin. Nonspecific resistance was highest 24 hr after injection of 10 mug of endotoxin. At this time, more than half of the mice survived challenge with 10(2) but not with 10(3)ld(50). Specifically immunized mice were resistant to as much as 10(5)ld(50), depending upon the route of immunization. Potency ratios for parenteral challenge were: nonspecific to normal, 100; specific to normal, 10(4) to 10(5); specific to nonspecific, 10(2) to 10(3). Employing aerosol challenge, specific immunization protected in the ld(100) range; nonspecifically immunized animals showed significant prolongation of survival time, but the 30-day mortality was similar to the control group.