[Immunology of inflammatory diseases of the digestive tract]

The etiology of inflammatory bowel diseases is unknown: infectious factors have been suspected but couldn't be confirmed. The multifactorial origin remains the most credible. The development of immunologic knowledge and in particular of the digestive immune system, has allowed to evoke the responsibility of immunologic abnormalities in the genesis, the chronicity or the recidive of inflammatory bowel disease, the more that the histologic lesions evoke an immune mediated pathology. An increased production of mucosal immunoglobulins exist in the inflammatory bowel diseases; some have a specificity for bacterial antigens; the activation of the complement is observed during acute access of the disease. Mucosal or circulating lymphocytes are cytotoxic in vitro for colonic epithelial cells, this reaction being modulated by seric factors and bacterial antigens. The T lymphocytes are increased in the mucosa without the ratio T helper/T suppressor being significantly modified. The immunoregulation is also perturbed, the modulation of the local immune reaction being altered essentially during the active phases of the disease. It is not clear yet whether this perturbation is primitive or secondary to inflammation. It seems reasonable to believe that the humoral and cellular responses to digestive antigens are the corollary of an enhanced antigenic absorption, of a more adequate antigenic presentation to the immune system, consequence of the expression of class II antigens by an inflamed mucosa and of an alteration of immune control.