Immunological memory provides long-term protection against pathogen re-infection and is the foundation for successful vaccination. We have previously shown an antigen-specific recall response in nurse sharks almost one year after primary exposure. Herein, we extend the time between prime and successful recall to >8 years, the longest period for which immunological memory has been shown in any non-mammalian vertebrate. We confirm that antigen binding is mediated by monomeric IgM and IgNAR, but not pentameric IgM, in both the primary and recall phases. Our inability to find target-binding clones in recombinant VNAR expression libraries suggests that, at least in this instance, antigen-specific memory cells comprise a small fraction of the IgNAR-positive B cells in epigonal and spleen. Further, that the few memory cells present can generate a robust antigen-specific IgNAR titer following re-stimulation. Our results continue to challenge the long-held, but erroneous, belief that the shark adaptive immune system is 'primitive' when compared to that of mammals.

中文翻译：

---

软骨鱼类长期免疫记忆的证据。

免疫记忆提供长期保护，防止病原体再次感染，是成功接种疫苗的基础。我们之前已经在初次接触后近一年的护士鲨中显示出抗原特异性回忆反应。在这里，我们将初级和成功回忆之间的时间延长至 > 8 年，这是在任何非哺乳动物脊椎动物中显示出免疫记忆的最长时期。我们确认抗原结合是由单体 IgM 和 IgNAR 介导的，而不是在初级和召回阶段由五聚体 IgM 介导。我们无法在重组 VNAR 表达文库中找到靶结合克隆表明，至少在这种情况下，抗原特异性记忆细胞包含表皮和脾脏中 IgNAR 阳性 B 细胞的一小部分。更远，存在的少数记忆细胞可以在重新刺激后产生强大的抗原特异性 IgNAR 滴度。我们的结果继续挑战长期以来但错误的观点，即与哺乳动物相比，鲨鱼适应性免疫系统是“原始的”。