Effects Of Chitosan On Immune Functions In Broiler Chickens And The Underlying Molecular Mechanisms

The present study was conducted to investigate the effects of chitosan on immune functions in broiler chickens and the underlying molecular mechanisms. The first three experiments were conducted by using the experimental technique in vivo. A total of 240 one-day-old Arbor Acre mixed-sex broiler chickens were randomly allotted to six dietary treatments with five replicates in each treatment, and with eight chickens in each replicate. The basal diet was mainly composed of corn and soybean. The broiler chickens in the six treatments were fed with the basal diets supplemented with 0 (control), 50, 200, 500, 1000 or 2000 mg/kg chitosan in a single factorial arrangement. The trial lasted for 42 days. The objective of the experiment 1 was to elucidate the effects of chitosan on humoral immune functions and cellular immune functions, and further to demonstrate the promotion of chitosan on immune functions of broiler chicks. The experiment 2 was conducted to investigate the effects of chitosan on endocrine secretion in broiler chicks. The experiment 3 was conducted to investigate the effects of chitosan on relative expression of iNOS mRNA and cPLA₂ mRNA in small intestine, and to elucidate the molecular mechanisms for chitosan to affect immune functions. The experiment 4 was conducted in vitro to demonstrate the effects of different levels of chitosan(0, 40, 80, 160 and 320μg/ml) on secretion functions and relative expression of iNOS mRNA and cPLA₂ mRNA of peritoneal macrophage, and further to investigate the molecular mechanisms by which chitosan modulated immune functions .Under the present experimental conditions, the results showed as follows:â‘ The dietary chitosan improved humoral immune functions and cellular immune functions in broiler chicks in a dose-dependent relationship. The supplementation of 500 - 1000 mg/kg chitosan improved the New castle disease antibody titer, T cell group contents and the concentrations of IgG, IgM and IgA, and then strengthen the immune functions of broiler chicks. However, the addition of 2000 mg/kg chitosan to diet was less effective.â‘¡Chitosan influenced concentrations of immunocyte factors(IL-1 and IL-2) and correlated hormone in serum of broilers in a quadratic dose-dependent manner(P<0.05). The supplementation of 500 - 1000 mg/kg chitosan improved the concentrations of IL-1, IL-2 and TNF-α, and suppressed the ACTH and COR contents. However, the addition of 2000 mg/kg chitosan to diet was less effective. This suggested that the effects of chitosan on immune functions was related to the levels of immunocyte factors and correlated hormones in serum of broiler chicks.â‘¢The experiment in vivo was conducted to study the molecular mechanisms for chitosan to modulate immune functions. The results showed that dietary chitosan supplementation enhanced NO content and iNOS activity in serum as well as iNOS mRNA relative expression in small intestine of broiler chickens in a quadratic dose-dependent manner(P<0.05), and the supplementation of 500-1000 mg/kg chitosan in the diet showed the better effects. The supplementation of 500-1000 mg/kg chitosan improved the concentrations of PLA₂,AA and PGE₂ in serum as well as cPLA₂ mRNA relative expression in small intestine of broiler chickens in a quadratic dose-dependent manner(P<0.05). But positive effects tended to be suppressed when the addition of chitosan in diet was increased to 2000 mg/kg.â‘£The experiment in vitro showed that chitosan could enhanced iNOS mRNA relative expression of peritoneal macrophage in broiler chicks(P<0.05), and promote the secretion of NO and iNOS in peritoneal macrophage. The addition of chitosan would also promote cPLA₂ mRNA relative expression and cPLA₂ activity of peritoneal macrophage(P<0.05), and increase the concentrations of PLA₂, AA, PGE₂ and LTB₄ in culture liquid. This suggested that the chitosan would promote the secretion functions of peritoneal macrophage in broiler chicks.⑤The present results implied that the mechanisms for chitosan to affect immune functions of broiler chickens were probably that chitosan activated expression of iNOS mRNA and improved iNOS activity and NO secretion; or that chitosan activated cPLA₂ mRNA expression and cPLA₂ activity, and promoted AA production which is synthesized from membrane phospholipid by cPLA₂.â‘¥In conclusion, the broiler chicks fed a diet containing 500-1000 mg/kg chitosan had higher immune functions compared with birds given a control diet.