Abstract
The envelope glycoproteins of Maedi-Visna virus consist of a surface glycoprotein (gpl35)
which is responsible for the characteristic spikes on the surface of the virion, and a
transmembrane protein (gp41) whose function includes linkage to the surface glycoprotein,
anchoring it to the virion envelope. The external glycoprotein is required for attachment to the
host cell via a receptor molecule present on the surface of the cell. Cells of the macrophage
lineage are the main target cells in MVV infection in vivo. The host humoral response is
targeted to the surface glycoprotein resulting in neutralizing antibody production. The
relevance of these antibodies is not understood as virus infection persists despite this active
immune response. The external glycoprotein has also been shown to be susceptible to
antigenic variation.
Expression of gpl35 as three overlapping fragments in the bacterial pGEX system was
undertaken with a view of using the recombinant protein as a source of immunogen to raise
monoclonal antibodies. These and the three recombinant fragments could be used for epitope
mapping. However, these fragments proved to be toxic to bacterial cells resulting in low yields
and high levels of contamination. In depth studies were carried out to improve the yield and
attempts were made to raise immune polyclonal sera. Characterization of these sera is
described.
Recombinant protein studies were extended to express gpl35 in the baculovirus expression
system. This resulted in a reliable source of recombinant protein that was devoid of
contamination and was easily purified. This protein was glycosylated and was recognised by
MW-infected sheep sera. Preliminary studies were carried out to determine its interaction
with sheep fibroblasts and hence its use to isolate the host cell receptor.
Attempts were made to raise monoclonal antibodies against gpl35 purified from virions by
lectin affinity chromatography. The development of a screening assay is described. This
approach did not result in the generation of any anti-gpl35 monoclonals. The preparation of
polyclonal antisera raised against two peptides within the external glycoprotein is reported.
