Intestinal epithelial cells as for the natural immune watchdogs system

he function of the mam- malian immune system is to eliminate or control invading pathogenic microorganisms. Viewed broadly, it has two components: the natural immune system, which mediates the nonspecific acute inflammatory response, and the adaptive immune response, which mediates antigen-specific immunity. The adaptive immune response can generate a practically unlimited var- iety of recognition molecules in the form of immunoglobulins and T cell receptors. These are used to screen for a large variety of foreign mol- ecules in the host. The adaptive im- mune response has the advantage that potential pathogens can be recognized with great specificity. Moreover, this system can improve its response after repeated exposure to a pathogen. A drawback is de- lay in mounting an immune re- sponse because, immediately after exposure, few immune cells are present that recognize an invading pathogen. This is a particular prob- lem for the interaction of the host with bacterial pathogens, which generally proliferate rapidly and so can quickly overwhelm the host. The natural immune system is in- herently better suited to deal quickly and effectively with rapidly multi- plying bacteria. Natural immunity involves the interaction of a lim- ited number of ‘foreign’ molecules with a large number of effector cells. To be effective, the natural immune system has developed to interact specifically with molecules that are common to many pathogens. For example, bacterial lipopolysacchar- ide (LPS), which is present on many important human bacterial patho- gens, initiates numerous cellular and humoral responses that pro- mote inflammation’. Further mol- ecules that activate cells of the natu- ral immune system include other bacterial-cell-wall components and