Abstract：
Immunosenescence corresponds to the progressive decline of immune functions with increasing age. Although it is critical to understand what modulates such a decline, the ecological and physiological drivers of immunosenescence remain poorly understood in the wild. Among them, the level of glucocorticoids (GCs) during early life are good candidates to modulate immunosenescence patterns because these hormones can have long-term consequences on individual physiology. Indeed, GCs act as regulators of energy allocation to ensure allostasis, are part of the stress response triggered by unpredictable events and have immunosuppressive effects when chronically elevated. We used longitudinal data collected over two decades in two populations of roe deer (Capreolus capreolus) to test whether higher baseline GC levels measured within the first year of life were associated with a more pronounced immunosenescence and parasite susceptibility. We first assessed immunosenescence trajectories in these populations facing contrasting environmental conditions. Then, we found that juvenile GC levels can modulate lymphocyte trajectory. Lymphocyte depletion was accelerated late in life when GCs were elevated early in life. Although the exact mechanism remains to be elucidated, it could involve a role of GCs on thymic characteristics. In addition, elevated GC levels in juveniles were associated with a higher abundance of lung parasites during adulthood for individuals born during bad years, suggesting short-term negative effects of GCs on juvenile immunity, having in turn long-lasting consequences on adult parasite load, depending on juvenile environmental conditions. These findings offer promising research directions in assessing the carry-over consequences of GCs on life-history traits in the wild.
摘要：
免疫衰老对应于免疫功能随年龄增长而进行性下降。尽管理解是什么调节了这种下降是至关重要的，免疫衰老的生态和生理驱动因素在野外仍然知之甚少。其中,生命早期的糖皮质激素(GC)水平是调节免疫衰老模式的良好候选者,因为这些激素会对个体生理产生长期影响.的确,GCs充当能量分配的监管者，以确保均衡，是由不可预测的事件触发的应激反应的一部分，并且在长期升高时具有免疫抑制作用。我们使用了二十年来在两个ro（Capreoluscapreolus）种群中收集的纵向数据，以测试在生命的第一年内测得的较高的基线GC水平是否与更明显的免疫衰老和寄生虫易感性有关。我们首先评估了面对不同环境条件的这些人群的免疫衰老轨迹。然后，我们发现，青少年GC水平可以调节淋巴细胞的轨迹。当GCs在生命早期升高时，淋巴细胞的消耗在生命后期加速。尽管确切的机制仍有待阐明，它可能涉及GC对胸腺特征的作用。此外,青少年的GC水平升高与成年期间出生在恶劣年份的个体的肺寄生虫丰度较高有关，提示GC对青少年免疫的短期负面影响，反过来会对成人寄生虫负荷产生持久的影响，取决于青少年的环境条件。这些发现为评估GCs对野外生活史特征的遗留后果提供了有希望的研究方向。
