Effects Of Dietary Chitooligosaccharide On Performance And Immune Function Of Piglets By Lipopolysaccharide Or Cydophosphamide Challenge

Two animal models (immune activation model, challenged with lipo-polysaccharide (LPS), immunosuppression model, challenged with cyclo-phosphamide (CY)) were established to evaluate the effect of Chitooligosaccharide (COS) on the immune function of weaning piglets and its underlying mechanism. A total of thirty-six weaned crossbred pigs (DurocxLandracexYorkshire,8.53±1.00kg) were randomly allocated into six groups with six replicates per group in two2×2factorial designs. In trial1, the main factors consisted of diet (0mg/kg COS vs.30mg/kg COS) and immunological activation challenge (LPS vs. sterile saline). In trial2, the main factors consisted of diet (0mg/kg COS vs.30mg/kg COS) and immunosuppression challenge (CY vs. sterile saline). Two trials were carried out at the same time, sharing the basal diet (0mg/kg COS) and the basal diet+30mg/kg COS treatments, without LPS or CY challenge. The trials lasted for18d. On day15-17, pigs were injected intraperitoneally with either80μg/kg BW of LPS or50mg/kg BW of CY, and the nonimmunological challenge group was injected an equivalent volume of sterile saline. Blood samples were collected3h and48h after the last injection. The liver, spleen and thymus were sampled after the last blood collection to determine the tissue gene expression.(1). LPS challenge significantly reduced average daily gain (ADG) and average daily feed intake (ADFI)(P<0.01) from days15-18. COS significantly alleviated the decrease of ADG induced by LPS, reduced feed/gain (P<0.01), and tended to enhance the ADFI (P=0.08) after challenge and the ADG (P=0.06) from1-18d. CY challenge significantly reduced ADG and ADFI (P<0.01). However, COS had not significantly alleviated the effect on the performance.(2).LPS challenge resulted in a remarkable elevation of spleen index (P<0.01), while CY injection had an opposite effect on spleen index (P<0.01). COS supplementation just alleviated the increasing caused by LPS in a certain degree.(3). There were no significant effect on neutrophils, lymphocytes, monocytes and white blood cell of piglets by LPS challenge. But COS supplementation and LPS challenge had a significant interaction effect on neutrophils (P<0.01) and white blood cells on3h post-challenge (P<0.05). CY challenge reduced the number of neutrophils, lymphocytes, monocytes and white blood cell on3h and48h post-challenge, and the supplementary of COS alleviated the decrease of monocytes (P<0.05) and tended to increase the lymphocytes (P=0.07).(4).There was no significant effect on the content of serum cortisol, C3, C4and lysozyme after3h by LPS challenge, but significantly increased cortisol levels on48h post-challenge (P<0.01). COS supplementation significantly reduced serum concentration of C3, C4, and increased lysozyme on3h post-challenge (P<0.05). There was a remarkable decrease on C3, C4in3h post-challenge and C3in48h post-challenge by CY (P<0.01), while significantly increased cortisol in48h after challenge P<0.01). COS addition increased lysozyme level on3h and48h post-challenge (P<0.05).(5) LPS injection significantly reduced IL-6and IL-10on3h post-challenge (P<0.05), increased TNF-a on3h post-challenge (P<0.05) and IL-1β, IL-2, IL-4on48h post-challenge (P<0.05). COS supplementation attenuated (P<0.05) the increasing in IL-1β, IL-2, IL-6level, and the reduction of IL-10, IFN-y level on3h post-challenge(P<0.05), and increased IL-4, IL-10concentrations on48h post-challenge (P<0.01). CY injection reduced serum IL-1β, IL-4, IL-6and IL-10on3h, and IL-6, IFN-y (P<0.05), TNF-a (P<0.01) on48h post-challenge, increased serum IL-2, IL-4on48h after challenge (P<0.05), while COS addition alleviated the decrease of IL-2, IL-4on3h, and TNF-a on48h after challenge (P<0.05).(6). LPS challenge increased (P<0.05) the relative mRNA expression of MyD88in spleen and TLR4, IRF3in thymus, reduced TRAF6mRNA expression in spleen (P<0.05). While COS alleviated (P<0.05) the up-regulation of TLR4, CD14, MyD88, NF-кB and IRF3mRNA expression in spleen, and NF-кB, TRIF mRNA in thymus. The NF-кB, TRIF mRNA in spleen and the TLR4, TRIF, IRF3mRNA in thymus were up-regulated by CY challenge (P<0.05). There were no significant effect on the genes expression of TLR4-MyD88independent signalling pathway by COS, but increased MyD88mRNA expression in the spleen (P<0.05).(7).The mRNA abundance of SIGIRR and Tollip was both increased remarkably (P<0.05) after the injection of LPS and CY in thymus, and30mg/kg COS supplementation tended to alleviate the increasing.The results showed that LPS administration enlarged the spleen of piglets, enhanced serum cortisol and inflammatory cytokines levels, and lead to systemic inflammatory reaction, eventually resulted in a decline in performance. While CY challenge suppressed the development of the spleen and the leukocyte differentiation, reduced immune function and growth performance of piglets. COS supplementation could effectively alleviate the injury of the spleen and the excessive activation of the immune response by LPS challenge, through the TLR4-MyD88dependent and independent signalling pathway. At the same time, COS could attenuated the immune suppression caused by CY challenge to some extent.