[Intestinal immune system]

The intestinal mucosa is the main barrier between a wide variety of potential antigens and human or animal beings. Beside of unspecific defense mechanisms there is a rather independently reacting gut associated lymphoid system (GALT), first described by Bienenstock. GALT is seen as part of a common mucosal immune system (MALT), the independency of which is based on morphological, functional and ontogenic reasons. The two main functional parts of GALT are Peyer's patches (with T-cells and B-cells) and the diffuse lymphoid tissue (DLT). The latter is found throughout the intestinal mucosa in two compartments, in the lamina propria and intraepithelially. However there is a network between different local immune systems and the humoral immune system which is demonstrated by the "homing" phenomenon of lymphocytes and "remote-site" stimulation. Although many basic mechanisms of intestinal immunity today are not completely understood, immunoprophylaxis against different enteropathogenic agents is successfully used either by active or by passive immunization methods.