Respiratory effect of Haemophilus influenzae endotoxin in mice.

The effect of the endotoxin of a noncapsulated Haemophilus influenzae strain isolated from bronchitis was studied on the respiration of mice. Inhalation of the H. influenzae endotoxin resulted in heavy attacks of dyspnoea with non-specific histological changes in the lung. The endotoxin elicited no direct response in isolated organs, but produced cytotoxic changes in HEp-2 tissue cultures. The experiments led to the conclusion that the clinical signs and the histological changes may be explained by the direct damaging effect of endotoxin on the cells and by the released mediator substances.