Purpose

A ventral heart positioned posterior to the branchial basket and equipped with a pericardium is homologous in tunicates and their sister group, the craniates, yet the tunicate model organism Ciona intestinalis features a pericardial body, a structure peculiar to few ascidian species. Here, we set out to distinguish between two competing hypotheses regarding the function of the pericardial body found in the literature: (H₁) The pericardial body performs a role in the removal of dysfunctional myocardial cells, and (H₂) it is a specialized niche of the immune system involved in defense against parasites.

Methods

We used histological techniques, transmission electron microscopy, and PCR-based gene sequencing to investigate whether individual ascidians parasitized with apicomplexan protists show signs of infections within the pericardial body.

Results

In individuals of C. intestinalis from the German North Sea infested with apicomplexan protists, the pericardial body contains numerous myocardial cells in various stages of degeneration while no remnants of parasitic cells could be identified.

Conclusion

Thus, we conclude that H₂—the pericardial body is a specialized niche of the immune system involved in defense against parasites—can be refuted. Rather, our observations support H₁, the hypothesis that the pericardial body performs a role in the removal of dysfunctional myocardial cells.

中文翻译：

---

小肠毛囊藻心包体含有血细胞和退化的肌细胞，但无寄生虫

目的

位于鳃篮后方并配备心包的腹侧心脏与被囊类动物及其姊妹群颅骨同源，但被囊类动物模型生物Ciona infantis具有心包体，这是少数海鞘物种特有的结构。在这里，我们着手区分文献中发现的关于心包体功能的两个相互竞争的假设：（H ₁）心包体在去除功能失调的心肌细胞中起作用，并且（H ₂）它是一种专门的参与防御寄生虫的免疫系统的生态位。

方法

我们使用组织学技术、透射电子显微镜和基于 PCR 的基因测序来研究寄生于 apicomplexan 原生生物的个体海鞘是否显示出心包体内感染的迹象。

结果

在来自德国北海的受顶端复合体原生生物侵染的肠衣原体个体中，心包体包含许多处于不同退化阶段的心肌细胞，而没有发现寄生细胞的残余。

结论

因此，我们得出结论，H ₂ - 心包体是参与防御寄生虫的免疫系统的一个专门生态位 - 可以反驳。相反，我们的观察结果支持 H ₁，即心包体在去除功能失调的心肌细胞中起作用的假设。