Virus-like particles in buffy coat cells of normal goats and goats infected with progressive pneumonia virus.

By electron microscopy, virus-like particles (VLP) were seen in neutrophils and lymphocytes from buffy coats prepared from 5 goats inoculated with progressive pneumonia virus (PPV) and 3 noninoculated goats. The VLP were 80 to 120 nm in diameter, limited by a unit membrane, and resembled PPV, visna virus, and other members of the oncornavirus family. Some VLP seemed to have electron-dense nucleoids and external spikes. In neutrophils, VLP were observed budding into vacuoles; rarely, intravacuolar clusters were seen. In lymphocytes, VLP were seen in vacuoles. Free VLP and budding of VLP from external cell surfaces were not seen. In vitro incubation of buffy coat cells with mitogens did not affect the frequency of VLP. Although the VLP are similar to PPV, the exact nature of the particles and their relationship to PPV is not clearly understood.