Reduced IL-37 Production Increases Spontaneous Chemokine Expressions in Colon Epithelial Cells

Microscopic colitis, comprising collagenous colitis and lymphocytic colitis, is a common cause of chronic diarrhea. Previously, we showed enhanced chemokine productions in microscopic colitis patients, indicating dysregulated immune cell chemotaxis in the immunopathogenesis. We also showed decreased mRNA of IL-37, mainly regarded as an anti-inflammatory cytokine, in the colonic mucosa of these patients, potentially an important factor for the chronicity of the colitis. Our aim in this study was to understand the possible role of IL-37 in chemokine production using a cell line model.

A colon epithelial cell line, T84, was stimulated with the TLR5 ligand flagellin. IL-37 protein production was reduced 20% using the CRISPR/Cas9 system, and the changes in chemokine mRNA and protein expressions were compared to cells transfected with empty plasmid.

The 20% reduction in IL-37 protein levels spontaneously increased CCL5, CXCL8, CXCL10, and CXCL11 mRNA and protein expressions. CCL2 mRNA and protein levels were enhanced upon TLR5 stimulation. CCL3, CCL20, and CX₃CL1 mRNA expressions were increased either spontaneously or following TLR5 stimulation, whereas CCL4 and CCL22 mRNA expressions were significantly decreased.

Even a minor decrease in the ability of colon epithelial cells to produce IL-37 results in altered chemokine expression, mainly an increase in the production of several chemokines. Our results indicate that a decreased IL-37 expression by colon epithelial cells may be an important factor for increasing the recruitment of immune cells and subsequently developing microscopic colitis.