Suppression of pulmonary antibacterial activity following Sendai virus infection in mice: dependence on virus dose

Pulmonary antibacterial defenses during mild and severe influenza virus infection

Severe influenza virus infections with pneumonic involvement are known to predispose the lungs to bacterial superinfections due to dysfunctions in the alveolar macrophage (AM) phagocytic system. To determine whether milder forms of influenza without pneumonic involvement have a similar outcome, pulmonary antibacterial defenses and AM phagocytosis were compared in murine models of mild and severe influenza virus A/HK/68 infections. Bactericidal activity was quantitated by the intrapulmonary killing of Staphylococcus aureus following aerosol challenge, whereas the functional capacity of the AMs was determined by Fc-receptor-mediated phagocytosis. With the severe virus infection, maximal suppression of bactericidal activity occurred on day 8 of infection and correlated with impairment of AM phagocytosis. A lesser but significant degree of suppression of pulmonary antibacterial defenses and AM phagocytosis was observed on the third day of the mild virus infection. The data demonstrate that mild influenza virus infections that are limited to the upper respiratory tract also impair pulmonary antibacterial defenses and may predispose the lungs to bacterial superinfections.

Evidence for defective neutrophil function in lungs of calves exposed to infectious bovine rhinotracheitis virus

Calves were exposed to an aerosol of infectious bovine rhinotracheitis (IBR) virus followed five days later by an aerosol of Pasteurella haemolytica. The animals were subjected to bronchoalveolar lavage before IBR and four days after, and again at 0, 4, 24, and 48 hours following Pasteurella haemolytica challenge. The results of these experiments suggest that neutrophil infiltration into the lung, in response to the presence of the bacteria was delayed thereby allowing the bacteria to become established in the lung. Neutrophils in infected animals displayed little random migration in vitro and did not respond to a chemotactic stimulus. It was also found that alveolar macrophages from virus-infected animals were not able to produce neutrophil chemotactic factors. These data suggest that the decrease in neutrophil chemotaxis and the lack of chemotactic factor production by the alveolar macrophage following infection with infectious bovine rhinotracheitis virus may predispose infected cattle to a secondary bacterial infection.

Dynamics of viral growth, viral enzymatic activity, and antigenicity in murine lungs during the course of influenza pneumonia

Mice were infected by aerosol inhalation with influenza A/PR8/34 virus, and the kinetics of infection were monitored by the measurement of infectious virus, viral neuraminidase activity, and viral antigen as detected by enzyme immunoassay. Pulmonary levels of neuraminidase activity closely paralleled the infectious titers quantitated by standard egg inoculation techniques. Both viral neuraminidase activity and viral antigen increased in a dose-dependent manner during the early stages of the viral infection. After day 5, however, viral neuraminidase activity precipitously declined, whereas viral antigen levels remained elevated at high concentration for up to 60 days. Immunosuppressive treatment with cyclophosphamide resulted in the prolonged maintenance of peak virus titers without any additional increases in viral antigen. Previously infected mice were resistant to reinfection with homologous virus as evidenced by the lack of detectable viral neuraminidase activity and the lack of generation of additional viral antigen. These data define the temporal relationship between levels of infectious virus, neuraminidase activity, and viral antigen in an experimental model of influenza virus infection.

Nonspecific suppressive effect of bovine herpesvirus type 1 on bovine leukocyte functions

The effect of bovine herpesvirus type 1 on the specific and nonspecific immune response of calves was examined. Animals with or without prior aerosol exposure to Pasteurella haemolytica serotype A1 were aerosol challenged with 10(8) PFU of virus. Blood and serum samples were taken before and after virus challenge for determining cell-mediated, humoral, and neutrophil responses. A significant depression of the blastogenic responses to phytohemagglutinin, P. haemolytica, and Pasteurella multocida and of neutrophil chemotactic response was observed 4 to 7 days after challenge. However, the antibacterial activity of neutrophils was not significantly affected by virus exposure. Anti-bovine herpesvirus type 1 antibody responses were detected 11 days postchallenge. A significant elevation of the anti-P. haemolytica antibody response (day 0 versus day +11) was detected in animals previously exposed to P. haemolytica.