Of note, infection with wild type M. marinum induced higher levels of pro-caspase-1 than ΔRD1, independent of the inflammasome (Figure 5B), which might be explained by secretion of Esat-6, a major Esx-1 substrate that has been proposed to induce caspase-1 gene expression in macrophages [22]. Here, ESX1 is linked to infection.