ABSTRACT
Interferons have been known for more than 30 years, especially for their anti-viral activities. It is also generally accepted that interferons play an important role in the host defense against viral infections. It is now well established that in addition to their antiviral activities interferons exert a wide variety of effects on physiological functions of normal cells. The ability of bacteria to penetrate the epithelial lining of the intestinal mucosa by invading the epithelial cells is an important mechanism for enteric disease. A correlation between the ability to produce disease in man and the ability to invade and survive inside epithelial-derived cell monolayer was demonstrated. A major problem in connection with in vitro invasiveness studies is to differentiate between intracellular and extracellular bacteria. It is often difficult if impossible to differentiate between bacteria attached to the surface and those internalized into the cells with conventional light microscopy.
