Bronchial hyperreactivity to histamine induced by Haemophilus influenzae vaccination.

Bronchial hyperreactivity to histamine 4 days following vaccination with the human respiratory pathogen Haemophilus influenzae was tested in two in vivo and one in vitro models. Conscious vaccinated guinea pigs exposed to aerosolized histamine became asphyxial significantly faster than saline-treated controls. Also the bronchoconstriction in anaesthetized guinea pigs as a result of i.v. histamine was significantly potentiated in the H. influenzae pretreated group. Isoprenaline (30 micrograms/kg) partially inhibited the bronchoconstriction. The difference in histamine sensitivity between the two groups however remained. Protection against bronchoconstriction by atropine on the other hand was significantly enhanced in the vaccinated animals. This suggests a hyperreactivity of the parasympathetic, cholinergic pathways as a result of H. influenzae vaccination.