As anadromous fish, sockeye salmon undergo complex endocrine changes when they return to their natal grounds to spawn. This is correlated with major immunological changes that will affect their response to pathogens. In spite of these challenges, salmon need to maintain sufficiently robust immunity to survive until spawning is complete, but the nature of immune adaptations during the spawning stage remains poorly understood. Our central question is to determine if sockeye salmon stimulate their immune system during the return migration and if so, whether this is a protective response. To begin answering this question, here we characterized the nature and timing of potential changes in anterior kidney immune fingerprints between salmon collected from seven different sites along the Kenai river, including the mouth of the river and two spawning sites. Our results revealed significant changes in abundance of B lineage, but not myeloid lineage cells during the spawning journey. This included early, transient and significant increases in abundance of both IgM⁺ and IgT⁺ B cells soon after fish entered the river, followed by a transient, significant increase in abundance of IgM⁺⁺ secreting cells in fish caught mid-river, and ending with a return to base levels of both cell populations in fish caught at spawning sites. Further, males appeared to have higher immune activation than females, as reflected by higher abundance of IgM⁺⁺ secreting cells, higher spleen index, and higher titers of serum IgM. Although roles for these newly generated IgM⁺⁺ secreting cells remain unclear at this time, the data complement our previous work which supported roles for long-lived plasma cells to protect returning salmon from pathogens at their natal grounds. We conclude that sockeye salmon are capable of inducing B cell responses during their spawning journey, with males having stronger responses compared to females. B cell activation during the return journey may provide returning adults with additional protection against pathogens not encountered as juveniles.

作为溯河鱼类，红鲑鱼在返回出生地产卵时会经历复杂的内分泌变化。这与将影响他们对病原体的反应的主要免疫学变化相关。尽管面临这些挑战，鲑鱼需要保持足够强大的免疫力才能在产卵完成前存活，但对产卵阶段免疫适应的性质仍知之甚少。我们的核心问题是确定红鲑鱼在返回迁徙过程中是否会刺激它们的免疫系统，如果是，这是否是一种保护性反应。为了开始回答这个问题，我们在这里描述了从基奈河沿岸七个不同地点收集的鲑鱼之间前肾免疫指纹潜在变化的性质和时间，包括河口和两个产卵点。我们的结果揭示了在产卵过程中 B 谱系丰度的显着变化，但不是髓系细胞。这包括 IgM 和 IgM 丰度的早期、短暂和显着增加⁺和 IgT ⁺ B 细胞在鱼进入河流后不久，随后在河中捕获的鱼中 IgM ⁺⁺分泌细胞的丰度短暂显着增加，并以捕获的鱼中两种细胞群的基本水平结束在产卵地点。此外，雄性似乎比雌性具有更高的免疫激活，这体现在更高的 IgM ⁺⁺分泌细胞丰度、更高的脾脏指数和更高的血清 IgM 滴度。虽然这些新生成的 IgM ^{++ 的作用}分泌细胞目前仍不清楚，数据补充了我们之前的工作，这些工作支持长寿命浆细胞的作用，以保护返回的鲑鱼免受其出生地的病原体的侵害。我们得出结论，红鲑鱼能够在产卵过程中诱导 B 细胞反应，与雌性相比，雄性的反应更强。返回过程中的 B 细胞激活可为返回的成年人提供额外的保护，以抵御在幼年时未遇到的病原体。