The host's intestinal flora provides the first line of defense against pathogens by preventing them from developing in the gastrointestinal tract, for instance by generating an inhibitory medium. Beneficial bacteria within the flora are able to interact with the adhesion and toxic effects of harmful bacteria. Ingested probiotic strains have a proven effect on the composition and metabolic activity of the intestinal microflora in healthy humans.
The intestinal epithelium constitutes a second line of defense and a true barrier against harmful bacteria, by the combined effect of the mucus layer and the epithelial cells themselves. Recent results support the hypothesis that consumption of probiotics may improve intestinal barrier function. However, these effects seem strain-specific and need to be further investigated.
The immune system constitutes the third defensive barrier against invasion. The innate immunity reacts immediately but unspecifically. The adaptive immunity takes longer but is specific and keeps memory of previous aggressions. A mild inflammatory state is necessary to keep the defense enabled, but the system must remain balanced in order not to start an inflammatory disease. Current scientific knowledge supports the hypothesis that consumption of certain lactic acid bacteria may modulate immune response.
Introduction
The Three Lines
Effect of probiotics on body's natural defenses.
