To address whether the ire-1-xbp-1 pathway is also activated in mammalian cells in response to a PFT, activation of the pathway was ascertained in HeLa cells exposed to the Aeromonas hydrophila PFT, aerolysin. As detected by the presence of the spliced protein isoform of XBP-1, treatment of mammalian cells with a PFT also results in robust activation of the ire-1-xbp-1 pathway ( Figure 1C ).