Analysis of HTLV-II syncytium formation using recombinant cowpoxvirus expressing the evelope precursor glycoprotein,gp63.

Abstract

P171 Infection by human T lymphotropic viruses type I and type II (HTLV-I and HTLV-II) results in cell membrane fusion or syncytium formation in vitro. The development of syncytium is considered to correlate with the susceptibility of cells to virus infection, and specifically with the interaction of the cellular receptor and the virus envelope glycoprotein. To investigate mechanisms of cell membrane fusion we have constructed a recombinant cowpoxvirus which permits expression of the HTLV-II envelope precursor glycoprotein, and have examined syncytia formation in a range of mammalian cell lines using an assay employing recombinant cowpoxvirus allowing the expression of HTLV-II envelope and the vaccinia virus T7 RNA polymerase, and a plasmid expressing β-gal under control of the T7 promoter. In this system, only cells fused with target cells turn the color blue, so that cell fusion can be detected with great sensitivity. Employing cell lines of human, mouse, rat, and monkey origin, although there was great variation almost all formed syncytia. We also investigated the levels of envelope glycoprotein expression and processing in cells exhibiting different degrees of syncytia formation using Western blotting methods. A clone of the monkey kidney cell line CV-1 which rarely and only poorly developed syncytia was found to have high levels of precursor glycoprotein gp63 expression and low levels of processing to gp46. Conversely cell lines which readily developed syncytia were found to have increased levels of gp46. We conclude that the cellular receptor for HTLV-II infection is widely distributed among different species and cell types, and that processing of the envelope precursor glycoprotein gp63 to gp46 and gp21 is necessary for the development of syncytia.