Early Socialization Triggered ROS-Mediated Activation of Canonical NF-κB Pathway Leading to Inflammation of Spleen in Suckling Piglets

Early socialization during lactation is advocated as a feeding strategy to reduce the weaning stress of piglets. However, early socialization has often been accompanied by more frequent aggression between individuals, and its effect on the immune system of piglets has yet to be evaluated. In this study, 89 piglets were raised separately under conventional feeding and early socialization environments. Based on differences in the aggressive behavior of the piglets in different environments during lactation, we further investigated the effects of early socialization on oxidative stress in the spleen of the piglets and the inflammatory responses involved in the canonical nuclear factor kappa-B (NF-κB) signaling pathway. The results revealed that early socialization led to a higher aggression level between individuals ( p < 0.01), increased malondialdehyde (MDA) and H 2 O 2 levels and inducible nitric oxide synthase (iNOS) activity, and inhibited glutathione (GSH) levels and the activities of catalase (CAT), superoxide dismutase (SOD), and glutathione peroxidase (GPX) in the piglet spleens ( p < 0.05). The mRNA expression levels of the protein kinase A (PKA), inhibitor of kappa B kinase-α (IKK-α), inhibitor of kappa B kinase-β (IKK-β), inhibitor of NF-κB-α (IκB-α), NF-κB(p65), interleukin-1β (IL-1β), interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α), cyclooxygenase-2 (COX2), iNOS, and heat shock protein (HSP) genes were significantly up-regulated, as well as the protein levels of P-p65, IKK-β, P-IkB-α, pro-IL-1β, and TNF-α. In summary, early socialization caused oxidative stress and inflammatory responses in the spleen of the piglets by inducing ROS production and the activation of the canonical NF-κB pathway. Our study revealed that early socialization significantly increased the ROS level in the piglet spleens and activated the canonical NF-κB signaling pathway, which induced a high expression of pro-inflammatory cytokines (TNF-α, IL-1β, IL-6, and COX2) and HSP genes regulated by NF-κB signaling, leading to oxidative stress and the inflammatory response.