These conditions predominate during early childhood and do not appear during any other stage of life (Snyder & Merson, 1982; Hoque et al., 1994), highlighting the particular vulnerability of the intestine during early development. Infections caused Silmitasertib supplier by enteric bacterial pathogens, such as diarrheagenic enterohemorrhagic (EHEC) and enteropathogenic (EPEC) Escherichia

coli, the family of attaching and effacing (A/E) bacterial pathogens, are among the most important causative pathogens of severe infantile diarrhea (Donnenberg & Whittam, 2001; Hecht, 2001; Vallance et al.,2002). The mouse pathogen Citrobacter rodentium causes a similar A/E lesion in the murine intestine and has been used as a physiological model of human infection of EPEC and EHEC E. coli. Using the C. rodentium model, we have shown that preinoculation of murine gut with Lactobacillus acidophilus, a probiotic strain, A-769662 nmr early in life can enhance host defense against enteric bacterial infection and attenuate bacteria-mediated intestinal injury (Chen et al., 2005). We also observed that probiotic treatment stimulates regulatory cytokine expression in

the colon transforming growth factor (TGF-β) (Chen et al., 2005). In line with these observations, it has been shown that breast-fed infants have a greater resistance to enteric pathogens owing to the transfer of commensal bacteria (Fanaro et al., 2003), nondigestible oligosaccharides (Newburg et al., 2005), TGF-β in maternal milk (Saito et al., 1993), and immunoglobulins (Brandtzaeg, 2010) which enhance development of the GAI. Moreover, targeted colonization of the neonate intestine with commensal microbiota has been shown to be effective in allergy prevention in later infancy (Lodinová-Zádníková et al., 2010). More specifically,

the intestinal microbial communities predominately induce the maturation of the mucosal adaptive immune system in the human neonate (Kaplan et al., 2011). Conversely, formula-fed infants lack maternal transfer of commensal bacteria, nondigestive oligosaccharides, and TGF-β which results in the modification of gut microbial communities compounding the vulnerability of the neonatal intestine to enteric pathogens (Le Huërou-Luron et al., 2010). TGF-β is a very potent negative regulator of mucosal inflammation Bupivacaine (Letterio & Roberts, 1998) inhibiting T cell activation (Letterio, 2005) vital to maintaining tolerance to innocuous antigens found within the intestine. TGF-β mediates cell signaling by ligand-dependent activation of heterodimeric transmembrane serine/threonine kinases receptors (Piek et al., 1999). Downstream, the ligand-activated receptor directly phosphorylates Smad2 and Smad3 proteins, which associate with Smad 4 and translocate to the nucleus to participate in transcriptional control of targeted genes (Heldin et al., 1997).