HBL-Like Toxins and Inflammasome Activation in Bacillus

Abstract

The innate immune system is the first line of host defence that can utilise pattern recognition receptors (PRRs) such as NLRP3 to detect and respond towards danger signals. Bacillus, particularly B. cereus, are food-borne pathogens known to produce hemolysin BL (HBL), a pore-forming toxin that can trigger NLRP3 inflammasome activation. This study investigates NLRP3 activation induced by four other Bacillus species aside from B. cereus and the mechanism required by their virulence factors to mediate this effect. To elucidate these, IncuCyte® Cytotoxicity Assay, western blot, ELISA, and LDH assay were performed for two different cell lines: THP-1 and B16F10 cells. Findings suggest that these virulence factors can trigger caspase-1 and gasdermin D (GSDMD) cleavage, resulting in increased pro-inflammatory cytokine IL-1β and IL-18 levels, as well as elevated dead cell percentage in the absence of NLRP3 inhibitor MCC950. Moreover, the role of Litaf and Cdip1 was deemed a necessity for mediating the activity of these virulence factors indicated by the distinct difference in effects on wild-type (WT) and knockout cells.