Effects of lipopolysaccharide administration on thymus damage, antioxidant capacity and immune function in weaned piglets.

Introduction: Piglets are vulnerable to stress during weaning because of changes in the feeding environment, nutrients, and other growth-impacting conditions. In this study, stress injury was modelled by continuous intraperitoneal injection of lipopolysaccharide (LPS) and was used to investigate the dynamics of antioxidant indices and immunoinflammatory factors in the piglet thymus.

Material and methods: Forty-eight weaned piglets were divided into an LPS group and a control group. One group was injected with LPS solution (100 μg/kg) and the other with sterile saline daily. The experiment ran over 13 days, and six piglets from each group were euthanised for necropsy on days 1, 5, 9 and 13. Thymic tissues were collected, and the antioxidant indices and mRNA expression levels of related genes were measured by enzyme activity assay and reverse-transcription quantitative PCR.

Results: In the LPS group, catalase activities were significantly increased on days 1 and 5, that of superoxide dismutase was significantly higher on day 9 and glutathione activity was elevated throughout. Messenger RNA (mRNA) expression of the toll-like receptor 4 (TLR4) pathway, interleukin (IL) 6, and IL-2 increased in the thymus on day 1. By day 5, the mRNA expression of the TLR pathway, the janus kinase (JAK)/signal transducer and activator of transcription (STAT) pathway, the kelch-like ECH-associated protein 1 (Keap1)/nuclear factor erythroid 2-related factor 2 (Nrf2) pathway, tumour necrosis factor α, IL-10, IL-6 and IL-2 were decreased. On day 13, the mRNA expression levels of the TLR4 and Keap1/Nrf2 pathways, TNF-α, IL-10 and IL-6 increased again.

Conclusion: Continuous LPS induction led to high activation of the thymic immune system in piglets during the prophase. However, this activation was accompanied by atrophy and immunosuppression mid-experiment. Nevertheless, the immune function gradually recovered in the later stages.