| Chickens have a special visual system and can detect a broader spectrum of colors than humans. Therefore, the chicken is extremely sensitive to subtle differences in light color. Our previous study showed that green light promotes cellular and humoral immune responses during the early stage, and blue light enhances immune responses during the later growth stages in the broilers. However, whether a combination of different monochromatic lights will result in better immune responses and its correlative mechanism needs to be confirmed.In this study, Arbor Acre male broilers were exposed to white light (W,400-700nm), red light (R,660nm), green light (G,560nm) and blue light (B,480nm) from0to26days by a LED system, then, the broilers were respectively switched to others color monochromatic lights until day49. The12kinds of different monochromatic lights combination (WR, WG, WB, RW, RG, RB, GW, GR, GB, BW, BR, BG) and4control groups (WW, RR, GG, BB) were formed. The results as followed:1. Effect of different monochromatic light combination on immune response in the broilersAt49days, the levels of anti-Newcastle disease virus (NDV) and anti-bovine serum albumin (BSA) IgG were the highest in GB group, and were elevated by11.66%～51.43%(P=0.000～0.044) and11.65%～43.33%(P=0.000～0.009)ascompared to single monochromatic lights,but there was no significant difference between the GB and BG groups.The peripheral blood T lymphocyte proliferation in the GB group showed an increased in vitro (12.38%～36.19%, P=0.000～0.013) compared with the other groups.However, there was little difference between GB and GW (P=0.112), BG (P=0.714) or BB groups (P=0.161). Theperipheral blood B lymphocyte proliferation in the GB group was significantly increased by12.96%～50.01%(P=0.000～0.004) than in other monochromatic light groups. No differences were found between the GB and BG group broilers.The IL-2concentration in the peripheral blood was the highest in the GB group, and was increased by9.68%～60.27%(P=0.000～0.025) over the single monochromatic light groups. But the TNF-α concentration in the peripheral blood in the GB group consistently remained lower than in the other groups, and it was lower16.88%～40.49%(P=0.000～0.002) than those in the single monochromatic light groups. No remarkable differences in the IL-2and TNF-α concentration of the GB and BG groups were observed.2. Effect of different monochromatic light combination on spleen development and lymphocyte proliferation in the broilersThe organ index of spleen in the GB group was higher by11.61%～36.26%(P=0.000～0.019) at49days compared to the broiler reared under the other single monochromatic light conditions. However, no significant difference was observed between the GB and BG groups. The diameter of splenic nodule in the GB group was higher by37.76%(P<0.001),64.84%(P<0.001) and10.72%(P=0.033) in comparison with broilers grown with WW, RR and GG, but the GB group was not significantly different from the BG (P=0.628) and BB (P=0.212) groups. The areas of periarterial lymphatic sheath in the GB group were raised by41.01%(P<0.001),75.36%(P<0.001)and19.84%(P=0.003) in comparison with WW, RR and GG groups. However, no significant difference was found between the GB and BG groups. The IOD of PCNA in the GB group was higher by23.09%(P<0.001),27.84%(P<0.001) and14.64%(P=0.007) than that of WW, RR and GG light groups. No significant differences were observed between the GB group and BG (P=0.459) or BB groups (P=0.058).The spleen T lymphocytes proliferation in GB group was higher18.33%～42.85%(P=0.000～0.003) than in WW, RR and GG light groups. However, spleen T lymphocyte proliferation in the GB group was not significantly different from the BG and BB group (P>0.05). The GB group showed enhanced B lymphocyte proliferation by11.90%～34.28%(P=0.000～0.018) compared to other light treatments.3. Effect of different monochromatic light combination on melatonin secretion and regulating lymphocyte proliferation in the broilersThe melatonin concentration of blood plasma or spleen in the GB group was the highest, and increased by21.97%～55.03%(P<0.001) and23.22%～71.93%(P=0.000～0.017) compared to the birds reared under all of the other light conditions at35d of age. The correlationanalysis indicate that a significant correlation (r=0.947and r=0.909) was observed between spleen lymphocyte proliferation with plasma or spleen melatonin level in different monochromatic light combination groups.The experiment in vitro showed that physiological level melatonin stimulated spleen T lymphocyte proliferation in different monochromatic light combination groups. Comparing to without melatonin treatment, the T lymphocyte proliferation was enhanced by12.44%～19.26%(P<0.05) in melatonin treatment groups, and thisproliferation trend was accordant with different light groups melatonin secretion.4. Effect of different monochromatic light combination on spleen lymphocyte antioxidative function in broilersAt49days, the activity of antioxidative enzymeGSH-Px and SOD in the GB groups were the highest, and increased by11.27%～58.66%(P=0.000～0.003) and12.18%～32.14%(P=0.001～0.026) compared to other light groups, but there was no difference between GB and BG group. T-AOC level in GB groups was also the highest, and it was higher than that of WW group (36.84%, P<0.001) and RR group (71.69%, P<0.001), but no significant difference among GB, BG, GG and BB groups. However, MDA content in GB groups was the lowest, and decrease21.18%～40.89%(P=0.003～0.044) compared to that of WW, RR and GG light conditions, but no significant difference among GB, BB and BGgroups (P<0.05).5. Effect of different monochromatic light combination on expression of melatonin receptor in thespleen ofbroiler.RT-PCR and Western blot results suggested that mRNA and protein expressionof Mel1a, Mel1b or Mel1c in the GB group were significant higher than that in othermonochromatic light,but no significant difference between GB and BG groups. ThemRNA or protein expressionin this three kinds ofmelatonin receptor showed Mel1b>Mel1c>Mel1a. Immunohistochemical localization in melatonin receptor showed that Mel1a-positive cells were primarily present in periellipsoid lymphatic sheaths and periarterial lymphatic sheath; Mellb-positive cells were found in the entire spleen tissue, including white pulp, red pulp and marginal zone; Mellc-positive cells were widely observed in ellipsoid, red pulp and marginal zone.6. Effect of signal pathway of melatonin on light color induced spleen T lymphocyte proliferation in the broilersThe results in vitro showed that extrinsic melatonin stimulating spleen T lymphocyte proliferation in the GB group was inhibited by melatonin receptor antagonist at35days. Compared to the control group, spleen T lymphocyte proliferation was decreased13.29%(P=0.028) by Mel1b selective antagonist (4P-PDOT), and was reduced11.05%(P=0.035) by Mel1c selective antagonist (prazosin), but it only descend6.34%(P=0.136) by Mel1a/Mel1b non-selective antagonist (luzindole) and no significant roles was observed in the spleen T lymphocyte proliferation. Further intracellular signal pathway study found that T lymphocyte proliferation in MEL+PD98059(ERK signal pathway blocking agent)and MEL+PDTC (selective antagonist of NF-κB) groups wererespectively decreased by13.05%(P=0.033) and13.97%(P=0.029) compare with MEL group. The result showed spleen T lymphocyte proliferation was obviously inhibited by two kinds of signal pathway blocking agent in broilers.Conclusion:Compared to single monochromatic light regimen, the light regimen, which green light was use in the early stage (0～26days) and blue light was adopted at a later age (27～49days), can better promote spleen development and enhance cellular and humoral immunity response, improving the immune function in broilers. The relative mechanism showed light color can affect broiler immune function through melatonin secretion in vivo. Howeveron the one hand, melatonincan enhance broiler spleen antioxidative ability by improving the enzyme activity of GSH-Px and SOD,on the other hand, melatonin would promote T lymphocyte proliferation and regulate immune through Mellb and Mellc receptor, which may be involved in ERK and downstream NF-κB signaling pathway... |
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