ELECTRON-MICROSCOPE STUDIES OF THE REPLICATION OF A BRITISH ISOLATE OF MAEDI-VISNA VIRUS IN MACROPHAGES AND SKIN CELL-LINES

The replication of EV1, a British isolate of maedi visna virus (MVV), in macrophages has not previously been studied, We therefore used tran smission and scanning electron microscopy (TEM and SEM respectively) t o compare the replication of EV in macrophages versus skin cell lines. Monocyte-derived macrophages (MDM), alveolar macrophages (AM) and ski n cell lines were all permissive for replication by EV1. Virus grew ra pidly and to high titers in skin cell lines and mature MDM. However re plication was slower in less mature MDM or AM. Virion budding occurred through (i) cytoplasmic membranes only (skin cells), (ii) cytoplasmic and vesicular membranes (MDM) or (iii) Yesicular membranes only (AM). This meant that virions accumulated in vacuoles within macrophages. R etroviral intracytoplasmic type A particles were seen in the cytoplasm of AM and MDM infected with strain EV1, but not MDM infected with str ain 1514 (an Icelandic MVV strain) and were shown to contain MVV gag a ntigen by immunogold staining.