Abstract
in English, Chinese Teleost peripheral blood contains a remarkably high proportion of B cells, accounting for 15%-50% of circulating lymphocytes. However, their immune responses to bacterial infection are yet to be elucidated. In the present study, 10× Genomics single-cell RNA sequencing (scRNA-seq) was employed to characterize the transcriptomic landscape of peripheral blood IgM + B cells in grass carp ( Ctenopharyngodon idella) following challenge with Aeromonas hydrophila, a major aquatic pathogen. Six transcriptionally distinct IgM + B cell subpopulations were identified, including (im)mature B cells, innate B cells, proliferating B cells, IgD high B cells, and two infection-induced subsets denoted as infection Ⅰ and Ⅱ B cells. Bacterial infection altered the cellular heterogeneity of IgM + B cells, triggered metabolic reprogramming in (im)mature and innate B cell subpopulations, and enhanced the immunological activation of circulating B cells. Notably, infection Ⅰ B cells demonstrated robust induction of interferon φ1 ( IFNφ1), a type I IFN, following A. hydrophila exposure. This induction was further validated through in vitro bacterial stimulation, indicating that teleost B cells actively contribute to innate antibacterial responses through IFN signaling. Additionally, the IgD high B cell subpopulation remained consistently present in peripheral blood across both infected and uninfected states, pointing to a constitutive and likely mature phenotype. These findings significantly advance our understanding of the heterogeneity of peripheral blood IgM + B cells and provide new insights into IgM + B cell-mediated immune responses in teleost fish. 硬骨鱼类B细胞在外周血中的浓度非常高，约占外周血淋巴细胞的15~50%。然而，硬骨鱼类外周血B细胞应对细菌感染的免疫应答机制仍有待解析。该研究利用10× Genomics单细胞测序技术来探究草鱼外周血IgM + B细胞在感染嗜水气单胞菌后的免疫应答。结果显示，草鱼外周血IgM + B细胞包含六个细胞亚群，分别是（未）成熟B细胞、先天样B细胞、增殖性B细胞、IgD high B细胞、感染I型B细胞和感染II型B细胞，后两种B细胞亚群是在细菌感染后才出现的新的B细胞亚群。细菌感染会改变外周血IgM + B细胞的异质性，驱动特定的IgM + B细胞亚群的代谢重编程，如（未）成熟B细胞和先天样B细胞，同时增强外周血IgM + B细胞的免疫功能。值得注意的是，感染I型B细胞展现出较高的I型干扰素（Interferon Ⅰ）— IFNφ1表达水平，这一结果通过体外嗜水气单胞菌刺激实验得到进一步验证，表明硬骨鱼类B细胞可以通过分泌IFNφ1参与抗菌防御。此外，草鱼外周血中普遍存在IgD high B细胞亚群，其存在与鱼体感染与否无关，提示其可能是一种成熟的B细胞类型。总而言之，这些发现极大地推进了我们对硬骨鱼类外周血IgM + B细胞异质性的认知，并为揭示硬骨鱼类IgM + B细胞介导的免疫应答提供了新见解。.