Mucosal Immunology is considered a new field of immunology. Mucosal immunology focuses on the aspects by which the antigens can enter the mucosal surface of the gastrointestinal tract

The intestine is a large contact surface to the outside; the intestinal epithelial cells not only produce multiple immunoregulatory cytokines, but also can alter the activity of antigen-presenting cells (APCs), so that they also present the MHC class I and II antigens. On the other hand, tannin has the ability to modify several immune parameters in poultry (MARZO et al., 1990; HEMPEL and ROHRBACH 1989) leading to various changes in the mucosal and systemic immune system of the intestine.

Overview of special features of the immune system at the poultry

Macrophages are central to the induction of specific immune responses; either via direct cell-cell contact or via soluble mediators (monokines, lymphokines). Microphages are capable of phagocytosis; These cells are the equivalent in birds to the mammalian neutrophils, in contrast to the mammalian neutrophils, these heterophile granulocytes lack the enzymes peroxidase and alkaline phosphatase (DAIMON and CAXTON-MARTINS, 1977). Basophilic granulocytes and mast cells play an important role in inflammatory reactions (FOX and SOLOMON, 1981). Also, the platelets in the bird have the ability to phagocytosis (CHANG and HAMILTON, 1979).

Natural killer (NK) cells are not clearly classed in the classical immune response, although they belong to the T cell series in mammals (HERBERMAN and ORTALDO, 1981) and possess Fc receptors (LAM and LINNA, 1979, 1980).  NK cells with cytotoxic activity against tumor cells have been detected in chicken (SHARMA and COULSON, 1979). Humoral elements of the nonspecific defense system are, for example, the fatty acids of the fatty glands, mucous substances and interferon-containing enzymes (lysozyme) occurring in body fluids (blood plasma, intestinal tract). (HERBERMAN and ORTALDO, 1981).

The Bursa Fabricii and the thymus of the bird form the central (primary) lymphatic organs. Both organs are fully developed only during a certain developmental phase and thus able to function and then regress. The undifferentiated progenitor cells, the stem cells, mature in these organs into immunocompetent,  also to antigenic reaction-capable, imprinted B-lymphocytes and T-lymphocytes; this is followed by emigration to the periphery. (FRANZ-VIKTOR, 1993; MOTICKA, 1975).

During the embryonic phase, when it is predominantly perceiving tasks of granulocytopoiesis and erythropoiesis, the bone marrow develops increasingly lymphocytopoietic activities at the time of hatching and thereafter (MOORE and OWEN, 1967, SETO, 1981); With progressive involution of the thymus and bursa fabricii, the bone marrow becomes more important as a peripheral (secondary) lymphatic organ. The first MHC-encoded products in chicken were blood group antigens (BRILES, 1960; SCHIERMAN and NORDSKOG, 1961). It became synonymous with the MHC of the Poultry introduced the term B complex. The MHC complex consists of 3 subregions (PINK et al., 1977) These subregions are, in analogy to the MHC nomenclature in Mammalia, certain functional classes namely assigned to class I and II.