Agriculture Reference
In-Depth Information
artiodactyls preventing exposure to foreign antigens, the mucosal immune system of the
neonatal piglet, particularly the adaptive immunity, is very poorly developed at birth. In
conventional environments, postnatal development occurs rapidly (Bailey
et al.
, 2001).
Collaboration between the innate and adaptive immune system confers appropriate
protection from harmful pathogens along with tolerance to ubiquitous dietary antigens
and microbiota (Bailey
et al.
, 2006, 2009). Excessive development or inappropriate
immune responses against 'harmless' antigens could result in transient allergic intestinal
damage. Excessive regulatory responses, suggested by the over-growth of largely non-
pathogenic bacteria, will result in microbial-mediated damage frequently associated with
post-weaning diarrhoea.
The objective of this review is to report on postnatal gut development in relation with the
microbiota establishment and how maternal diet may modulate such a developmental
profile. We first report on features of the gut and those of the gut-associated lymphoid
tissues in normal newborn piglets, and on how the maternal environment could affect
such characteristics. We emphasize modifications of bacterial colonization of the gut
with treatment of the gestating and lactating sow with antibiotics or maternal diet
supplementation with prebiotics. A focus on impaired gut maturity of piglets suffering
intra-uterine growth retardation is also made. Finally, the impacts of dietary sow
supplementation with n-3 polyunsaturated fatty acids are discussed.
15.2
Gut and gut-associated lymphoid tissue development
During the foetal period, the gut must acquire the ability to digest food and absorb
nutrients, to set up defence mechanisms against pathogenic bacteria, eliminate exogenous
toxins and tolerate commensal microbiota and food antigens. Indeed, the gut is a complex
tissue with major functions of selective absorption and digestion. As the first epithelial
barrier of the body, the intestinal epithelium must also control the passage of exogenous
agents that participate in the maturation of the local immune system present in the
intestine (Calder
et al.
, 2006). Several components participate in the innate defence
system of the intestine, such as mucosal secretions (mucus layer, lysozymes, antibacterial
peptides, etc.), the physical epithelial barrier (formed by the intercellular tight junctions),
the phagocytic cells (macrophages, neutrophils), the mast cells, the glycoconjugates
express on epithelial cells that mimic receptor bacteria, and intestinal motility. The
adaptive defence system (or specific immunity) of the gut-associated lymphoid tissues
(GALT) consists of the lymphoid tissue associated with the intestine [Peyer's patches
(PP) and mesenteric lymph nodes (MLN), which act as inducers of mucosal immune
responses] and of a more diffuse zone, the lamina propria being the effector of the local
immune response. The PP, the MLN and the lamina propria contain antigen presenting
cells and B and T lymphocytes which all participate in this local immune activity.
15.2.1
Organization of the gut-associated lymphoid tissues
The intestinal immune system (or GALT) is considered as the first immune organ since
it contains 70 to 85% of immune cells present in the body. The GALT is generally divided
