The Role of Probiotics in Atopic Dermatitis Prevention and Therapy

Development of the child’s immune system tends to be directed toward a T-helper 2 (Th2) phenotype in infants, whereas postnatal maturation is associated with gradual inhibition of Th2 and increasing Th1 affinity [1]. Thus, immature Th2-dominant neonatal responses must undergo environment-driven maturation via microbial contact in the early postnatal period to prevent development of childhood allergic diseases. Nevertheless, nowadays the increased use of antimicrobial medication, the consumption of sterile food, and reduced family size that result in lower rates of infection during childhood also reduce early contact to microbes. Consequentially, at an early age the infant`s immune system results in subsequent polarization toward a Th2 phenotype during postnatal maturation. Among several other phenomena, the present increase in allergic diseases seen in the industrialized countries has been attributed, to a relative lack of microbial stimulation of the infantile gut immune system and the exaggerated hygiene of the typical western lifestyle during early childhood. And this is known as the hygiene hypothesis [2]. The newborn is first colonized by microbes at birth. The colonization of the gut that begins promptly after birth is affected by mode of delivery, early feeding strategies and the hygienic conditions around the child (the early environment). The colonizing bacteria originate mainly from the mother's gut and vaginal tract [3]. For instance, children born by cesarean section are colonized with Bifidobacteria and Lactobacilli later than vaginally delivered children, and are shown to have more frequent respiratory allergies [4]. After delivery, breastfeeding continues to enhance the original inoculum by the introduction of specific lactic acid bacteria, Bifidobacteria and bacteria from the mother's skin, all of which enable the infant gut microbiota that is dominated by Bifidobacteria. Breast milk also contains plentiful indigestible oligosaccharides, which pass through the whole intestine and promote the growth and activity of commensal bacteria; composed mainly of Bifidobacteria [5]. These bacteria set the basis for gut microbiota development and modulation, along with environmental exposures such as antibiotic administration. The greatest differences between breast-fed and formula-fed infants appear to be in lactic acid bacteria and Bifidobacteria colonization. Usually, Bifidobacteria appear after birth and, within a week, are reported as the dominant bacterial group, with Bifidobacterium (Bfdbm) infantis / longum / breve being the most common species in breast-fed infants [6]. In addition, Lactobacillus (Lctbs) acidophilus is the most common Lctbs in the feces of breast-