Claudin 1 is a 23 kDa multi-pass membrane protein in the Claudin family of epithelial tight junction proteins. Claudin-1 is expressed by epithelial cells in a wide variety of tissues as well as in Langerhans cells and dendritic cells. It is up or downregulated in many cancers and is required for the entry of hepatitis C virus into hepatocytes. It mainly expresses the peripheral neuroma （partial type of negative）, derivative skin fibrous sarcoma, fibroma and deity fibroma.