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Abstract
Most viral and bacterial infections occur via mucosal epithelial surfaces of the respiratory, gastrointestinal and genital tracts.
The mucosal immune system is the first line of physical and immunological defense against invading pathogens through innate and acquired immunity. Mucosal surfaces represent a large surface area of contact of the body and the external environment. The ability of the immune system to distinguish between dangerous and non-dangerous agents is essential for mounting protective immune response.
The main functions of the mucosal immune system are:
1) Protection from harmful microbial pathogens (anti-infectious role),
2) Prevention of penetration of excessive amounts of antigen to the circulation (barrier function),
3) Low reactivity to harmless antigens present on mucosal surfaces (Oral, mucosal tolerance).
The mucosal immune system uses a number of mechanisms to protect the host against an aggressive immune response to luminal constituents. These include a strong physical barrier, mucosal colonization with commensal microflora, generation of antimicrobial molecules and unique way of antigen presentation.
Characteristic features of mucosal immunity distinguishing it from systemic immunity include existence of characteristic populations of lymphocytes, which differ from the blood and spleen lymphocytes either in their origin, phenotype, repertoire or in secreted products, the colonization of the mucosas by cells originating from the lymphoid follicles of the intestine or the respiratory tract (migration and homing of mucosal lymphocytes) forming the so called “common mucosal immune system” and also the long known transport of polymeric immunoglobulins (secretory immunoglobulins).