CD4⁺ helper T cells play key and diverse roles in inducing adaptive immune responses in vertebrates. The CD4 molecule, which is found on the surfaces of CD4⁺ helper T cells, can be used to distinguish subsets of helper T cells. Teleosts are the oldest living species with bona-fide CD4 coreceptors. Although some components of immune systems of teleosts and mammals appear to be similar, many physiological differences are represented between them. Previous studies have shown that two CD4 paralogs are present in teleosts, whereas only one is present in mammals. Therefore, in this review, the CD4 molecular structure, expression profiles, subpopulations, and biological functions of teleost CD4⁺ helper T cells were summarized and compared with those of their mammalian counterparts to understand the differences in CD4 molecules between teleosts and mammals. This review provides suggestions for further studies on the CD4 molecular function and regulatory mechanism of CD4⁺ helper T cells in teleost fish and will help establish therapeutic strategies to control fish diseases in the future.

CD4 ⁺辅助 T 细胞在诱导脊椎动物的适应性免疫反应中发挥着关键而多样的作用。^{在 CD4 +}辅助 T 细胞表面发现的 CD4 分子可用于区分辅助 T 细胞的亚群。硬骨鱼是最古老的具有真正 CD4 辅助受体的生物。尽管硬骨鱼和哺乳动物的免疫系统的某些组成部分看起来相似，但它们之间存在许多生理差异。先前的研究表明，硬骨鱼中存在两种 CD4 旁系同源物，而哺乳动物中只有一种。^{因此，在本综述中，硬骨鱼 CD4 +}的 CD4 分子结构、表达谱、亚群和生物学功能总结了辅助 T 细胞，并与它们的哺乳动物对应细胞进行了比较，以了解硬骨鱼和哺乳动物之间 CD4 分子的差异。本综述为进一步研究硬骨鱼CD4 ⁺辅助性T细胞的CD4分子功能及调控机制提供了建议，有助于未来制定控制鱼类疾病的治疗策略。