Stimulation of microbicidal host defence mechanisms against aerosol influenza virus infection by lentinan

The ability of polysaccharide immunomodulator lentinan to stimulate non-specific resistance against respiratory viral infections was investigated. Significant protection was conferred by lentinan administered intranasally before lethal influenza virus infection and could be corroborated by a reduction of the lung virus titres. Since the lung is the target organ of influenza virus infection, lentinan was also administered by the intravenous route. Lentinan conferred complete protection against a LD75 challenge dose of virulent influenza virus and significantly prolonged the survival time after a LD100 challenge. The effect on respiratory burst of broncho-alveolar macrophages was investigated by luminol-dependent chemiluminescence (CL) in response to stimulation by zymosan. Enhanced CL activity was present at an early stage in groups receiving lentinan. Significant nitric oxide activity could also be stimulated by culturing broncho-alveolar macrophages in the presence of lentinan. TNF activity could not be detected in lung lavage but measurable IL-6 was produced already after 6 h in animals administered lentinan alone and in lentinan-pretreated influenza virus-infected mice. Influenza virus alone did not induce measurable IL-6 at 6 h but high activity was present at later time periods.