Mucosal immunity: aliment and ailments

The development of the primitive gut in the multicellular aquatic eukaryote was driven by the insufficient absorption of nutrients from the oceanic soup. The anatomy of this evolving specialized system invited its colonization by environmental prokaryotes and resulted in the establishment of the intestinal microflora. Innate immunity had previously evolved in gutless organisms such as plants and was fully functional in the gut of invertebrates. On the other hand, adaptive immunity evolved in vertebrates, most probably because of some selective pressure such as the adaptation to a predatory lifestyle. Interestingly, this form of immunity was localized first in their primitive gut. Although the newly generated eukaryote-prokaryote relationship in the gut evolved under mutualistic principles, its symbiotic nature is easily interrupted by extrinsic factors such the composition of the consumed food. Thus, it is argued below that a state of disequilibrium with the microflora (dysbiosis) results in potentially serious immune-related disadvantages to the host.