Vertebrate cellular immunity displays substantial variation among taxa and environments. Hematological parameters such as white blood-cell counts have emerged as a valuable tool to understand this variation by assessing the immunological status of individuals. These tools have long revealed that vertebrate cellular immune systems are highly plastic and respond to injury and infection. However, cellular immune systems may also be able to anticipate a high risk of injury from environmental cues (e.g., predation-related cues) and respond plastically ahead of time. We studied white blood-cell (leukocyte) profiles in African cichlids Pelvicachromis taeniatus that were raised for 4 years under different levels of perceived predation risk. In a split-clutch design, we raised fish from hatching onwards under chronic exposure to either conspecific alarm cues (communicating high predation risk) or a distilled water control treatment. Differential blood analysis revealed that alarm cue-exposed fish had twice as many lymphocytes in peripheral blood as did controls, a condition called lymphocytosis. The presence of a higher number of lymphocytes makes the cellular immune response more potent, which accelerates the removal of invading foreign antigens from the bloodstream, and, therefore, may be putatively beneficial in the face of injury. This observed lymphocytosis after long-term exposure to conspecific alarm cues constitutes first evidence for an anticipatory and adaptive plastic response of the cellular immune system to future immunological challenges.

脊椎动物的细胞免疫在分类和环境之间显示出很大的差异。诸如白细胞计数之类的血液学参数已成为通过评估个体的免疫状态来了解这种变异的有价值的工具。长期以来，这些工具已经揭示出脊椎动物的细胞免疫系统具有高度的可塑性，并对损伤和感染有反应。但是，细胞免疫系统也可能能够预见到环境提示（例如与捕食相关的提示）造成伤害的高风险，并提前做出可塑性反应。我们研究了非洲慈鲷Pelvicachromis taeniatus中白细胞（白细胞）的分布在不同的感知掠夺风险水平下提高了4年。在分体式离合器设计中，我们在长期暴露于特定警报提示（传达高捕食风险）或蒸馏水控制处理的情况下，从孵化开始养鱼。差异血液分析显示，暴露于提示信号的鱼外周血中的淋巴细胞数量是对照组的两倍，这种情况称为淋巴细胞增多。大量淋巴细胞的存在使细胞免疫反应更加有效，从而加速了从血流中清除入侵的外来抗原，因此在受伤时可能是有益的。