Gal-lectin-dependent contact activates the inflammasome by invasive Entamoeba histolytica.

Entamoeba histolytica (Eh) is an extracellular protozoan parasite of the human colon, which occasionally breaches the intestinal barrier. Eradicating ameba that invades is essential for host survival. A defining but uncharacterized feature of amebic invasion is direct contact between ameba and host cells. This event corresponds with a massive pro-inflammatory response. To date, pathogen recognition receptors (PRRs) that are activated by contact with viable Eh are unknown. Here we show that the innate immune system responds in a qualitatively different way to contact with viable Eh vs. soluble ligands produced by viable or dead ameba. This unique Eh Gal-lectin contact-dependent response in macrophages was mediated by activation of the inflammasome. Soluble native Gal-lectin did not induce inflammasome activation, but was sufficient for transcriptional priming of the inflammasome and non-inflammasome-dependent pro-inflammatory cytokine release. We conclude the inflammasome is a pathogenicity sensor for invasive Eh and identify for the first time a PRR that specifically responds to contact with intact parasites in a manner that accords with scale immune response to parasite invasion.