[Urinary tract immunology].

The human urinary tract represents an impressive mechanical barrier against infection. Its immediate anatomical proximity to the gastrointestinal tract predisposes it to invasion and infection by enteric bacteria. Thus the immune system of the urinary tract represents an essential and powerful means to repel bacterial, viral and parasitic intruders, protecting sensitive organ systems such as the kidneys. The innate immune system comprises specific urothelial surface receptors named Toll-like receptors that sense small molecules derived from pathogens and initiate an early immune response. The adaptive immune system encompasses both cellular (T-lymphocytes) and humoral effectors (antibodies). Secretory immunoglobulin A, which mediates the mucosal immune response, is of particular importance. The complex cross-linking for innate and adaptive immune response as well as humoral and cellular effectors is the key to the urinary tract immune system and to its defense against pathogenic microorganisms.