Shiga toxin 1 targets bovine leukemia virus-expressing cells

Direct evidence that Escherichia coli Shiga toxin (Stx) acts against bovine leukemia virus (BLV)-expressing cells was obtained. The active A subunit of Stx type 1 (StxA1) targeted a selected population of permeable cells expressing BLV and inhibited BLV replication in a culture of bovine peripheral blood mononuclear cells. Cells were cultured with and without StxA1, and at various times cells expressing BLV were identified by being stained with MW1 monoclonal antibody specific for the BLV protein gp51. Before culture, permeable cells were tagged by uptake of one of the following: acetoxymethyl of 2',7'-bis-(2-carboxyethyl)-5-(and 6)-carboxyfluorescein (BCECF), BCECF conjugated to 70-kDa dextran, or 70-kDa dextran conjugated to fluorescein. The tagged cells costaining with anti-gp51 were selectively eliminated in StxA1-treated cultures. Electron microscopy analysis of purified B lymphocytes showed sharply reduced numbers of BLV particles in StxA1-treated cultures.