Morphogenesis of bovine leukemia virus

Abstract

The morphogenesis of bovine leukemia virus (BLV) was studied in short-term cultures of leukocytes from cows with persistent lymphocytosis and in BLV-producing cell lines. Few budding particles were found. They consisted of one shell underneath the cell membrane with granules attached to the inner side. When the shell is completed the budding particle could follow two pathways: It could (a) bud from the cell membrane to give rise to a free immature particle or (b) mature while still in contact with the cell, by condensation of the shell and the granules into a nucleoid, and subsequently bud from the cell membrane as a mature virion. A different pathway of morphogenesis, probably followed by the majority of the virions, is proposed based on the following observations: (1) Low numbers of budding particles on the cell membrane, (2) condensation of electrondense material within the cytoplasm resembling virus particles in the first stage of budding, and (3) immature and mature particles lying free in the cytoplasm. This pathway of morphogenesis suppose the formation of immature and mature particles within the cytoplasm without a budding process. Immunoferritin studies on these BLV-producing cells using bovine and goat anti-BLV sera have shown labeling of the BLV particles. The cell surface, however, was labeled only rarely and then in small areas. This means that on the cell surface of BLV-producing cells very few viral structural polypeptides are present. A comparison of the morphology of BLV and several other oncornaviruses leads to the conclusion that the morphogenesis of BLV is different from that of the type B and C and other similar particles such as Mason-Pfizer monkey virus and bromodeoxyuridine-induced guinea pig leukemia virus.