Alteration of pulmonary macrophage function by respiratory syncytial virus infection in vitro

Alveolar macrophages (AL) are the first line of defense against inhaled pathogens and are exposed to virus during the course of a respiratory syncytial virus (RSV) infection. Interference of virus with alveolar macrophage functions may contribute to the risk of aquiring secondary bacterial infections during or after respiratory tract infections with RSV or other viral agents. We studied whether murine AL get infected with RSV and whether they support viral replication in vitro. In addition, the effects of RSV on microbicidal and on immunoregulatory functions were examined. Only a subpopulation of AL expressed viral F proteins after exposure of these cells to RSV. Infected AL released only small amounts of infectious virus into the supernatant. The extent of virus replication in AL seemed to be dependent in part on the amount of IFN induced by the virus, as has been demonstrated by infection of lung tissue macrophages and AL in vitro.