Kinetics of Haemophilus influenzae type B infection in normal and ribosome-immunized mice using intraperitoneal and intracerebral routes of inoculation.

The kinetics of infection was studied in normal and ribosome-immunized mice challenged with Haemophilus influenzae Type b organisms. Ribosomal preparations extracted by the differential-centrifugation and sodium-dodecyl-sulphate treatment or ammonium-sulphate-precipitation procedures were highly immunoprotective when mice were challenged by the i.p. route. After i.p. injections, organisms rapidly spread to blood, liver, lungs and brain in normal and immunized mice. However, by 24 h after injection, evidence of organism clearance could be seen in immunized mice. By 32 h organisms were cleared from blood, brain and lungs of all immunized mice and from spleens in 2 of 3 mice. However, organisms persisted in high numbers of unimmunized mice until their death by 48 h. These data indicate that i.p. injections of H. influenzae mixed with gastric mucin leads to a true infection and can be used as a model to evaluate immunoprotective activity. The kinetics of infection induced by intracerebral (i.c.) inoculation also was studied. The LD50 for this type of infection was more than 1000 times the LD50 for i.p. infection. The patterns of infection induced by i.c. challenge were similar in normal and immunized mice and immunoprotection could not be detected using this model.