The roles and functions of Paneth cells in Crohn's disease: A critical review

Paneth cells (PCs) are located at the base of small intestinal crypts and secrete the α-defensins, human α-defensin 5 (HD-5) and human α-defensin 6 (HD-6) in response to bacterial, cholinergic and other stimuli. The α-defensins are broad-spectrum microbicides that play critical roles in controlling gut microbiota and maintaining intestinal homeostasis. Inflammatory bowel disease, including ulcerative colitis and Crohn's disease (CD), is a complicated autoimmune disorder. The pathogenesis of CD involves genetic factors, environmental factors and microflora. Surprisingly, with regard to genetic factors, many susceptible genes and pathogenic pathways of CD, including nucleotide-binding oligomerization domain 2 (NOD2), autophagy-related 16-like 1 (ATG16L1), immunity-related guanosine triphosphatase family M (IRGM), wingless-related integration site (Wnt), leucine-rich repeat kinase 2 (LRRK2), histone deacetylases (HDACs), caspase-8 (Casp8) and X-box-binding protein-1 (XBP1), are relevant to PCs. As the underlying mechanisms are being unravelled, PCs are identified as the central element of CD pathogenesis, integrating factors among microbiota, intestinal epithelial barrier dysfunction and the immune system. In the present review, we demonstrate how these genes and pathways regulate CD pathogenesis via their action on PCs and what treatment modalities can be applied to deal with these PC-mediated pathogenic processes.