Dept. of Ecology and Evolutionary Biology, Cornell University, 215 Tower Rd, Ithaca, NY 14853, USA; Cornell Lab of Ornithology, 159 Sapsucker Woods Rd, Ithaca, NY 14850, USA.
Dept. of Ecology and Evolutionary Biology, Cornell University, 215 Tower Rd, Ithaca, NY 14853, USA; Cornell Lab of Ornithology, 159 Sapsucker Woods Rd, Ithaca, NY 14850, USA.
Horm Behav. 2024 Apr;160:105500. doi: 10.1016/j.yhbeh.2024.105500. Epub 2024 Feb 4.
The immune system can be modulated when organisms are exposed to acute or chronic stressors. Glucocorticoids (GCs), the primary hormonal mediators of the physiological stress response, are suspected to play a crucial role in immune modulation. However, most evidence of stress-associated immunomodulation does not separate the effects of glucocorticoid-dependent pathways from those of glucocorticoid-independent mechanisms on immune function. In this study, we experimentally elevated circulating corticosterone, the main avian glucocorticoid, in free-living female tree swallows (Tachycineta bicolor) for one to two weeks to test its effects on immune modulation. Natural variation in bacteria killing ability (BKA), a measure of innate constitutive immunity, was predicted by the interaction between timing of breeding and corticosterone levels. However, experimental elevation of corticosterone had no effect on BKA. Therefore, even when BKA is correlated with natural variation in glucocorticoid levels, this relationship may not be causal. Experiments are necessary to uncover the causal mechanisms of immunomodulation and the consequences of acute and chronic stress on disease vulnerability. Findings in other species indicate that acute increases in GCs can suppress BKA; but our results support the hypothesis that this effect does not persist over longer timescales, during chronic elevations in GCs. Direct comparisons of the effects of acute vs. chronic elevation of GCs on BKA will be important for testing this hypothesis.
当生物体暴露于急性或慢性应激源时，免疫系统可以被调节。糖皮质激素（GCs）是生理应激反应的主要激素介质，被怀疑在免疫调节中发挥关键作用。然而，大多数与应激相关的免疫调节证据并没有将糖皮质激素依赖途径的影响与糖皮质激素独立机制对免疫功能的影响分开。在这项研究中，我们通过给自由生活的雌性北美树燕（Tachycineta bicolor）注射一到两周的循环皮质酮（鸟类主要的糖皮质激素）来实验性地升高其皮质酮水平，以测试其对免疫调节的影响。细菌杀伤能力（BKA）的自然变异（一种先天固有免疫的衡量标准）可由繁殖时间和皮质酮水平之间的相互作用来预测。然而，皮质酮的实验性升高对 BKA 没有影响。因此，即使 BKA 与自然变异的皮质酮水平相关，这种关系也可能不是因果关系。实验对于揭示免疫调节的因果机制以及急性和慢性应激对疾病易感性的影响是必要的。其他物种的研究结果表明，GCs 的急性增加可以抑制 BKA；但我们的结果支持这样的假设，即在较长时间内慢性升高 GCs 时，这种效应不会持续存在。比较急性和慢性升高 GCs 对 BKA 的影响对于检验这一假设将非常重要。
