Glucan alteration of pulmonary antibacterial defense

Particulate yeast glucan, prepared by the methods of Northcote and Horne and Peat et al, was studied in rats and mice to determine its protective capacity in respiratory infection. Glucan was administered intravenously to rodents prior to infection with aerosols of bacteria. Glucan-treated rats had significantly increased rates of phagocytosis and killing of Staphylococcus aureus immediately after infection and minimal increases at 4 h. In contrast, pulmonary killing of Klebsiella pneumoniae in rats was markedly enhanced by glucan at 4 h. Glucan treatment of mice provided only transient protection against pulmonary infection with group C streptococci. Histological studies demonstrated greatly increased numbers of macrophages in the lungs of glucan-treated rats; the lungs of glucan-treated mice appeared normal. These results show that glucan can enhance intrapulmonary bacterial killing. In rats, this is due to the ability of glucan to increase the number of lung macrophages resulting in increased bacterial ingestion. Glucan-induced protection in mice is less clear.