Mucosal immune system
The mucosal immune system is the immune system of mucous membranes – thin, permeable barriers between the body and the outside environment. These include the lining of the gut, the lungs, eyes, nose, mouth, uterus and vagina.
Mucosal surfaces in the body are immunologically linked. Antibodies created by infection at one mucous membrane site migrate throughout the body.  For example, Heliobacter pylori infection in the stomach seems to prevent asthma in mice. Intranasal immunization protects against vaginal HSV-2 infection. Mice infected with influenza virus suffer damage in both the lungs and the gut even in the absence of viral replication in the gut.