Intestinal epithelial cells (IECs) are the first to encounter luminal antigens and play an active role in intestinal immune responses. We previously reported that β‐glucans, major fungal cell‐wall glycans, induced chemokine secretion by IEC lines in a Dectin‐1‐ and Syk‐dependent manner. Here, we show that in contrast to β‐glucans, stimulation of IEC lines with Candida albicans and Saccharomyces cerevisiae did not induce secretion of any of the proinflammatory cytokines IL‐8, CCL2, CXCL1, and GM‐CSF. Commensal fungi and β‐glucans activated Syk and ERK in IEC lines. However, only β‐glucans activated p38, JNK, and the transcription factors NF‐κB p65 and c‐JUN, which were necessary for cytokine secretion. Furthermore, costimulation of IEC lines with β‐glucans and C. albicans yielded decreased cytokine secretion compared to stimulation with β‐glucans alone. Finally, ex vivo stimulation of human colonic mucosal explants with zymosan and C. albicans, leads to epithelial Syk and ERK phosphorylation, implying recognition of fungi and similar initial signaling pathways as in IEC lines. Lack of cytokine secretion in response to commensal fungi may reflect IECs’ response to fungal glycans, other than β‐glucans, that contribute to mucosal tolerance. Skewed epithelial response to commensal fungi may impair homeostasis and contribute to intestinal inflammation.

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Intestinal epithelial cells (IECs) are the first to encounter luminal microorganisms and actively participate in intestinal immunity. We reported that IECs express the β-glucan receptor Dectin-1, and respond to commensal fungi and β-glucans. In phagocytes, Dectin-1 mediates LC3 associated phagocytosis (LAP) utilizing autophagy components to process extracellular cargo. Dectin-1 can mediate phagocytosis of β-glucan-containing particles by non-phagocytic cells. We aimed to determine whether human IECs phagocytose β-glucan-containing fungal particles via LAP. Zymosan (β-glucan particle) and Heat-killed and UV inactivated C. albicans were phagocytosed by monolayers of human colonic (n=18) and ileal (n=4) organoids and IEC lines. LAP was identified by LC3 and Rubicon recruitment to phagosomes and lysosomal processing of internalized particles was demonstrated by co-localization with lysosomal dyes and LAMP2. Phagocytosis was significantly diminished by blockade of Dectin-1, actin polymerization and NAPDH oxidases. Our results show that human IECs sense luminal fungal particles and internalize them via LAP. This novel mechanism of luminal sampling suggests that IECs may contribute to the maintenance of mucosal tolerance towards commensal fungi.