Weaning causes imbalanced T lymphocyte distribution and impaired intestinal immune barrier function in piglets

Context The immune system of piglets is not fully developed at weaning. The immature adaptive immune system along with the change in the feed types and the living conditions make piglets susceptible to pathogenic infections, and result in diarrhoea and decreased growth. However, the underlying mechanisms require further research. Aims This study was conducted to investigate the effects of weaning on the growth performance and intestinal immune function of piglets. Methods In total, 40 piglets with similar bodyweights were selected in pairs at 21 days old and divided into the suckling group (SG, breastfed by their mothers) and weaning group (WG, weaned at 21 days old). Eight piglets from each group were randomly selected and sacrificed at 24 days (SG3 and WG3) and 28 days of age (SG7 and WG7). The growth performance, T lymphocyte subpopulations, the concentration of cytokines and immunoglobulins, and the expression of Notch2 signalling proteins were determined. Key results The weaning caused a decrease in bodyweight (P < 0.01) and the ratio of CD3+CD4+/CD3+CD8+ T cells in the thymus (P < 0.05). Compared with SG3, the concentration of secretory immunoglobulin A (sIgA) in the jejunum was decreased, and that of interleukin 2 (IL-2) in serum and ileum, IL-1β and IL-2 in jejunum were upregulated (P < 0.01), while IL-10 in the small intestine was downregulated (P < 0.05) in WG3. Weaning downregulated gene expression of IL-4 and upregulated gene expression of IL-1β, IL-12, and interferon γ (IFN-γ) in small intestine (P < 0.05). Weaning downregulated protein expression of Notch2 and Hes1 but upregulated Jagged1 expression in small intestine of piglets (P < 0.05). Conclusions Weaning caused an imbalance in T lymphocyte distribution, thus impairing the intestinal immune function of piglets, which might be associated with the Notch2 signalling. Furthermore, weaning caused adverse effects on piglets especially on the first 3 days, which were partly recovered after 3 days, but still existed at 7 days after weaning. Implications The results of this study may guide the pig-raising industry, especially for the management of piglets shortly after weaning.