EFFECT OF BVD VIRUS-INFECTION ON ALVEOLAR MACROPHAGE FUNCTIONS

Alveolar macrophages (AM) were recovered by bronchoalveolar lavage fro m a group of eight calves at various times before and after inoculatio n with a cytopathic respiratory isolate of bovine viral diarrhoea viru s (BVDV). A second group of four calves were given tissue culture medi um as a control inoculum. Macrophages were also recovered from two add itional, uninoculated calves, and were exposed to BVDV in vitro. Tests were carried out on the recovered macrophages to determine the effect s of the virus on several functional properties. Immunofluorescence di d not indicate the AM as being readily susceptible to this isolate of BVDV, although infection did occur. Fc receptor (FcR) and complement r eceptor (C3R) expression, phagocytosis and microbicidal activity and t he production of neutrophil chemotactic factors were all significantly reduced in macrophages recovered from BVDV infected calves, compared with pre-inoculation control levels, whereas the control inoculated ca lves displayed significant increases in some of the functions. With ma crophages exposed to the virus in vitro however, only FcR and C3R expr ession and phagocytic activity were significantly reduced. The results demonstrate that BVDV can reduce local immune defences in the lung, f ollowing infection by the respiratory route, and in conjunction with t he other immunosuppressive properties of BVDV would favour a pre-dispo sing role for the virus in the pathogenesis of respiratory disease in calves.