Because IL-22 receptor (IL-22R1) is not expressed in immune cells, but on epithelial and stromal cells including intestinal and respiratory epithelial cells, skin keratinocyte, hepatocytes, colonic subepithelial myofibroblasts, pancreatic acinar cells, and RA FLS(14,15). This evidence concerns the gene IL22RA1 and rheumatoid arthritis.