Immunostimulating agents against influenza virus infection in senescent rats.

This study investigated the nonspecific immunomodulatory effects of Bacillus Calmette-Guerin (BCG), muramyl dipeptide (MDP) and ascorbic acid (vitamin C) on virus infection of the respiratory tract in Fischer-344 rats. Groups of young adult (12-16 months old) and aged (24-30 months old) rats were given BCG or MDP intranasally or vitamin C orally 6 weeks and again 3 days before an intranasal challenge with influenza virus A/Bangkok/H3N2 (10(6) 50% EID). Titers of hemagglutinin in lung homogenates and the presence of leukocytes in the respiratory tracts served as indices of infection. Lung macrophage functions of animals were determined by measuring random migration and phagocytic yeast cell killing in vitro. Clearance of Staphylococcus aureus from the respiratory tracts of the animals was also measured 4 hours after challenge. - Following BCG treatment, significantly fewer animals developed virus infection. MDP and vitamin C treatments also reduced the numbers of infected rats but did not differ significantly from the untreated control groups. BCG and MDP treatments significantly reduced the numbers of lung leukocytes in virus infected animals. Mean virus titers in the lung homogenates were significantly lower in all treatment groups by the third day of infection. Following all treatments, duration of virus infection was significantly shorter in the aged compared to the young adult groups. Lung macrophage functions increased in all treatment groups. The improvement of aged groups over their controls was greater than that of the young adults compared to their controls. BCG had the greatest protective effects in both the young adult and aged animals; MDP and vitamin C, in that order, were less effective.(ABSTRACT TRUNCATED AT 250 WORDS)