Understanding nutritional immunomodulation: Th1 versus Th2

In order to modulate or influence the immune response or responsiveness of an animal by nutrition it is important to understand the basic immune effector mechanisms and factors influencing these. A fundamental knowledge on the intricate communication of the immunocompetent cells, their ontogeny and their induction sites and signals is required for understanding dietary modulation and/or enhancement of immune responsiveness. Moreover, a good understanding of the intimate relationship between the resident bacterial flora/pathogens and the host intestinal tract is quite important. In general we can distinguish two main categories in this search, a search for food components which have a direct effect on the pathogen or gut flora and secondly those which have an indirect effect on the gut pathogen or flora by targeting the intestinal and/or immune cells of the host. Some compounds (if not all) act even in both ways. The first category of compounds includes medium-chain fatty acids killing pathogens, sugars or lectins inhibiting colonization of the gut by competition or blocking, and competition in colonization by changes in the resident flora. The second group of modulators targets the innate immune system of the host by interacting with host receptors. To understand this innate immune alertness of the mucosal tract, it is imperative to focus on the acute phase of the inflammatory response. A lot of food components such as vitamins A and D, w6/w3 fatty acid ratios, oligosaccharides and others can indeed stimulate/modulate innate immunity at the mucosal site and protect against intestinal invaders. However, their mechanisms of action are not always fully understood and are now under thorough investigation. More recently, new groups of receptors, including the Toll-like and NOD receptors, have been discovered, which specifically recognize certain molecular patterns common in the microbial world, and referred to as pathogen-associated molecular patterns (PAMPs). These patterns are characteristic for lipopolysaccharides, lipoproteins, peptidoglycans, glycolipids and other molecules of microbial/yeast/fungal origin. They are present in abundance in the gut microbial flora and can be exploited in animal feeds to induce an immune alertness for mucosal protection against pathogens. Indeed, these PAMPS interact with pathogen recognition receptors (PRR) of the gut and, depending on the type of activated receptor, trigger warning signals that can modulate the acquired im