| Summary: | The extracellular envelope glycoprotein (gp135) of maedi-visna virus interacts with cellular receptor molecules and is the major target of neutralsing antisera <i>in vivo</i>. Antigenic drift of gp135 may have an important role in viral persistence. In order to begin to investigate the roles of different regions of gp135, yeast and bacterial expression systems were used to generate recombinant protein and gp135 was expressed as 3 overlapping fragments. There have been no published reports of expression of recombinant gp135 proteins. By using the proteins to screen sera from infected sheep it was shown that sheep vary in the regions of gp135 to which they mount an antibody response detectable in this system. At least 3 epitopes on gp135 are recognised by sera from infected sheep. The recombinant proteins were used to investigate interactions of gp135 with cellular molecules, and as immunogens to raise gp135-specific sera. Possible future experiments using these reagents are suggested. gp135 fragments derived from different viral stocks of the British isolate of maedi-visna virus were sequenced, to obtain a preliminary estimate of the extent of the variability of the gene. The data suggested the presence of both relatively conserved and variable regions in gp135.
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