Lazado Carlo C, Skov Peter Vilhelm, Pedersen Per Bovbjerg
Technical University of Denmark, DTU Aqua, Section for Aquaculture, The North Sea Research Centre, DK-9850, Hirtshals, Denmark.
Technical University of Denmark, DTU Aqua, Section for Aquaculture, The North Sea Research Centre, DK-9850, Hirtshals, Denmark.
Fish Shellfish Immunol. 2016 Aug;55:613-22. doi: 10.1016/j.fsi.2016.06.040. Epub 2016 Jun 23.
The present study investigated the daily dynamics of humoral immune defenses and the temporal influence in the sensitivity of these responses to a bacterial endotoxin in Nile tilapia (Oreochromis niloticus). The first experiment subjected the fish to two photoperiod conditions, 12L:12D (LD) and 0L:24D (DD), for 20 days to characterize the rhythms of humoral immunity. Serum alkaline phosphatase (ALP), lysozyme (LYZ), peroxidase (PER) and protease (PRO) exhibited significant rhythmicity under LD but not in DD. No significant rhythms were observed in esterase (ESA) and anti-protease (ANTI) in both photoperiod conditions. Fish reared under LD were subsequently subjected to DD while the group previously under DD was exposed to LD, and this carried on for 3 days before another set of samples was collected. Results revealed that the rhythms of LYZ, PER and PRO but not ALP persisted when photoperiod was changed from LD to DD. Nonetheless, immune parameters remained arrhythmic in the group subjected from DD to LD. Cluster analysis of the humoral immune responses under various light conditions revealed that each photic environment had distinct daily immunological profile. In the second experiment, fish were injected with bacterial endotoxin lipopolysaccharide (LPS) either at ZT3 (day) or at ZT15 (night) to evaluate the temporal sensitivity of humoral immunity to a pathogen-associated molecular pattern. The results demonstrated that responses to LPS were gated by the time of day. LPS significantly modulated serum ALP and ANTI activities but only when the endotoxin was administered at ZT3. Serum LYZ and PER were stimulated at both injection times but with differing response profiles. Modulated LYZ activity was persistent when injected at ZT3 but transient when LPS was applied at ZT15. The magnitude of LPS-induced PER activity was higher when the endotoxin was delivered at ZT3 versus ZT15. It was further shown that plasma cortisol was significantly elevated but only when LPS was administered at ZT3. On the other hand, plasma melatonin was significantly affected by LPS injection but only when exposed at ZT15. Taken together, this study shows that several key components of humoral immunity in tilapia exhibit circadian rhythms and adapt to photoperiodic changes. Further, results of the bacterial endotoxin challenge suggest that responsiveness of serum humoral factors to a biological insult is likely mediated by the time of day, highlighting the importance of circadian rhythm in the immunological functions of fish.
本研究调查了尼罗罗非鱼（Oreochromis niloticus）体液免疫防御的每日动态变化以及这些反应对细菌内毒素敏感性的时间影响。第一个实验将鱼置于两种光周期条件下，即12小时光照：12小时黑暗（LD）和0小时光照：24小时黑暗（DD），持续20天，以表征体液免疫的节律。血清碱性磷酸酶（ALP）、溶菌酶（LYZ）、过氧化物酶（PER）和蛋白酶（PRO）在LD条件下呈现出显著的节律性，但在DD条件下没有。在两种光周期条件下，酯酶（ESA）和抗蛋白酶（ANTI）均未观察到显著的节律。随后，将在LD条件下饲养的鱼置于DD条件下，而之前处于DD条件下的组则暴露于LD条件下，并持续3天，然后收集另一组样本。结果显示，当光周期从LD变为DD时，LYZ、PER和PRO的节律持续存在，但ALP的节律不存在。然而，从DD转换到LD的组中免疫参数仍然无节律。对不同光照条件下体液免疫反应的聚类分析表明，每个光照环境都有独特的每日免疫学特征。在第二个实验中，在生物钟时间3（白天）或生物钟时间15（夜晚）给鱼注射细菌内毒素脂多糖（LPS），以评估体液免疫对病原体相关分子模式的时间敏感性。结果表明，对LPS的反应受一天中的时间限制。LPS显著调节血清ALP和ANTI的活性，但仅当内毒素在生物钟时间3给药时。在两个注射时间点，血清LYZ和PER均受到刺激，但反应模式不同。当在生物钟时间3注射时，LYZ活性的调节是持续的，但当在生物钟时间15应用LPS时是短暂的。当内毒素在生物钟时间3给药时，LPS诱导PER活性的幅度高于生物钟时间15。进一步表明，血浆皮质醇仅在生物钟时间3给予LPS时显著升高。另一方面，血浆褪黑素仅在生物钟时间15暴露于LPS时受到显著影响。综上所述，本研究表明罗非鱼体液免疫的几个关键成分表现出昼夜节律并适应光周期变化。此外，细菌内毒素攻击的结果表明，血清体液因子对生物刺激的反应性可能受一天中的时间介导，突出了昼夜节律在鱼类免疫功能中的重要性。
