Effect of NLRP3 deficiency on cytotoxic and IL-15-producing activities of synthetic candidalysin peptide

Objectives: Candidalysin (CL), a hydrophobic peptide toxin secreted by Candida albicans, is a key virulence factor that contributes to cytolysis, tissue damage, and immune activation. CL is thought to exert some of its biological activities, including IL-15 production, through the activation of the NLRP3inflammasome pathway. To date, the mechanism by which CL affects human NLRP3 is not fully understood. We investigated specific activities of synthetic CL peptides using human-derived NLRP3-deficient cells.Methods: Two distinct synthetic CL peptide solutions were prepared: CLd, with CL completely solubilized as nanoparticles in dimethyl sulfoxide, and CLw, with CL partly solubilized in water, and including insoluble microparticles. THP-1 human monocytic cells and NLRP3-deficient THP-1 cells were differentiated into macrophages and stimulated with these peptide solutions. Cell membrane damage, lactate dehydrogenase release, IL-15 production, and caspase-1 activation in stimulated cells were subsequently evaluated.Results: Both CLd and CLw exhibited cytotoxic activities independent of NLRP3. Importantly, CLd induced IL-15 production and caspase-1 activation in an NLRP3-independent manner, whereas these activities in CLw-stimulated cells were entirely NLRP3-dependent, suggesting that the NLRP3-dependent response might be triggered by insoluble microparticles.Conclusions: Our results demonstrate that inherent CL activities can cause cell damage and IL-15 production in an NLRP3-independent manner. Our research advances the elucidation of the role of NLRP3 in CL biological activity, underscoring the necessity for further exploration of the precise mechanisms underlying the NLRP3-independent effects of CL and providing novel insights into the complexity of host -pathogen interactions.(c) 2023 Japanese Association for Oral Biology. Published by Elsevier B.V. All rights reserved.