Piglet weight gain during the first two weeks of lactation influences the immune system development

•Piglets’ immune system development is affected by birth weight and early growth performances.•Expression of genes involved in defense response and oxidative stress was modulated in LWG piglets.•Intestinal antigen presenting cells markers (APC) were decreased in LWG piglets.•The increase of B cells in HWG piglets was not observed in LWG piglets.•The regulation of various biological processes supporting neonatal development is associated to maternal lactocrine signaling. The aim of this study was to investigate the effect of the piglet growth during the first week of life on ileal expression of genes and on development of the immune system. Eight litters adjusted to 12 piglets were used. Within each litter, the piglet that showed the lowest weight gain (LWG; n = 8) and the one that showed the highest weight gain (HWG; n = 8) in their first week of life were enrolled. Peripheral blood mononuclear cells (PBMC) were isolated on days 8 and 16 to characterize cellular population profiles and to assess ex-vivo secretion of interleukin-10 (IL-10), IL-6 and tumor necrosis factor-α (TNF-α). On day 16, piglets were euthanized and ileum samples were collected to extract RNA for microarray analysis and gene expression by qPCR. As expected, growth performance of LWG piglet was impaired compared to HWG piglets (P