When CathB was silenced, a significant reduction in the expression of Hsr203 was observed following infection with E. amylovora, suggesting that cathepsin B is genetically upstream of Hsr203. Consistent with this observation, applying various cathepsin B inhibitors (Z-FA-FMK, Ac-LVK-CHO, CA-074-Me and Z-FGNHO-Bz) reduced the HR response. Here, CTSB is linked to infection.