Mucosa are widely distributed in the human body,coveting the surface of the respiratory,intestinal and urinary tract.Mucosal immune system is a particular part of the whole immune system.Different parts of mucosa can be connected by lymphocyte homing,which results in a common immune response.Lymphocyte homing is a multi-step process involving a series of integrias,selectins,chemokines and their receptor family,etc.In different mucosa,there may be different homing receptors responsible for the homing process.