Abstract Background Altered monocyte-derived macrophage (MdM) responses to gut microbes are a key feature of Crohn’s disease (CD) pathology, but how these cells respond to intestinal fungi remains unclear. Candida albicans exists as a commensal yeast in the human intestine, but changes in local environment or host immunity can induce normally spherical yeast to form toxin-producing filaments 1. C. albicans strain-dependent triggering of the inflammasome/IL-1β axis in MdM correlates with endoscopic Mayo scores in colitis patients 2, but further mechanistic insight is limited due to mice not being natural hosts of C. albicans and unable to fully replicate human anti-fungal responses 1. This study therefore developed a novel 3D intestinal model to investigate how human gut-adapted C. albicans strains interact with host tissues to drive mucosal inflammation in CD. Methods THP1 monocytes (wild-type, NLRP3-knockout, NLRC3-knockout) and primary MdM from CD and HC donors were used in tandem with a novel 3D intestinal model. The model consisted of a silicon 3D-printed frame, a fibrin hydrogel (“lamina propria”) with CCD-18Co fibroblasts and THP1 monocytes, a HUVEC-lined vascular channel and Caco2 epithelial surface. C. albicans isolated from healthy control (HC) or CD gut biopsies were inoculated into 2D in-vitro assays and 3D models to probe human host-fungal interactions. Results Upon C. albicans challenge, THP1 cells and primary MdM expressed more IL-1β when exposed to a filamentous CD-derived strain compared with a HC strain, which required both NLRP3 and NLRC4 for maximal cytokine release (Fig. 1). Intriguingly, Candida failed to upregulate the NLRP3 priming signal NF-kB or key effector protein caspase-1 in THP1 cells, and THP1NLRC4-/- cells displayed impaired phagocytosis and upregulated gasdermin-D (GDD) expression when challenged with all gut-adapted Candida strains and inert fluorescent fungal particles. In contrast, Caco2 epithelial cells and CCD-18Co fibroblasts were resistant to Candida-induced IL-1β and IL-18 expression, despite rapid upregulation of GDD. A 3D gut model was developed with epithelial surface and intact barrier function, a hydrogel based ‘lamina propria’ replete with fibroblasts and monocytes, and a readily accessible vascular channel (Fig. 2). The CD-derived strain grew extensive destructive filaments/colonies on the model epithelium leading to expression of GDD but not IL-1β or IL-18. Subsequent fibroblast upregulation of GDD indicated a downstream role for 3D cell-cell interactions. Conclusion A novel immunocompetent intestinal model was used to investigate human host-fungal interactions, suggesting a major role for C. albicans in epithelial barrier damage and differential inflammasome activation. References: 1.Prieto, D., et al., Adaptation of Candida albicans to commensalism in the gut. Future Microbiol, 2016. 11(4): p. 567-83. 2.Li, X.V., et al., Immune regulation by fungal strain diversity in inflammatory bowel disease. Nature, 2022. 603(7902): p. 672-678. Conflict of interest: Carlson, Sean: Grants: Wellcome Trust Clinical Research Fellowship Conference attendance support from Tillotts Pharma AG Mathew, Liya: No conflict of interest Pardieu, Claire: No conflict of interest Hindle, Sarah: No conflict of interest Khan, Maryam: No conflict of interest Blowes, Liisa: No conflict of interest Munro, Carol: No conflict of interest Connelly, John: No conflict of interest Stagg, Andrew: Grants: Wellcome Trust Clinical Research Fellowship Conference attendance support from Tillotts Pharma AG Lindsay, James: Investigator Initiated Research Grant: Takeda, Abbvie, Gilead Personal Fees: I have received fees for speaking and may have received support to attend academic conferences from: Abbvie UK/Global, Bristol Myers Squib, Cornerstones US, Gilead, Galapagos, Lilly, MSD UK, Ferring UK, Ferring Intl., Celltrion, Takeda, Pfizer, Janssen, Tillotts, Other: I serve of the advisory board of Abbvie UK/Global, Alpini, Astra Zeneca, Engytix, Galapagos, Gilead, GSK, Lily, MSD, Ferring UK, Ferring Intl., Celltrion, Takeda, Pfizer, Janssen, Shattucks Laboratory, McCarthy, Neil: NEM has received consultancy fees and funding for research from ImCheck Therapeutics SAS and TC BioPharm.
Carlson et al. (Thu,) studied this question.