Background：CD103 is a type I transmembrane glycoprotein known as aE integrin or Integrin aIEL chain. It belongs to the integrin family and is primarily found on intestinal intraepithelial lymphocytes （IEL）. CD103 is also expressed on a subpopulation of lamina propria T cells, epithelial dendritic cells, lamina propria-derived dendritic cells, and a small subset of peripheral lymphocytes. T regulatory cells express high level of CD103. The CD103 expression on lymphocytes can be induced upon activation and TGF-b stimulation. In association with integrin b7, CD103 is expressed as aE/b7 heterodimer. Mature CD103 protein can be cleaved into 2 chains, a 150 kD （C-terminal） chain and a 25 kD （N-terminal） chain, which remain linked by disulfide bonds. CD103 binds to E-cadherin and mediates homing of lymphocytes to the intestinal epithelium.
