Evolutionary Characteristics and Immune Response of Il-17 Ligand and Receptor Families in Megalobrama amblycephala Following Aeromonas hydrophila Infection.

The Il-17 ligand family members (Il-17s) and their receptors (Il-17rs) are core immune regulatory gene families against bacterial infection in vertebrates, while their evolutionary characteristics and immune functions remain poorly understood in Megalobrama amblycephala. This study systematically identified Il-17s and Il-17rs in M. amblycephala, analyzing their evolutionary characteristics and immune response mechanisms. Sequence alignment and domain analysis showed that all Il-17s contained the conserved Il-17 domain, while most Il-17rs possessed the SEFIR domain. Furthermore, these genes showed isoform-specific distribution characteristics in gene structure and conserved motifs. Phylogenetic and Collinearity analyses indicated that the Il-17rs in teleosts had undergone significant gene duplication, subject to strong purifying selection pressure, with il-17d and il-17rd1 demonstrating the highest evolutionary conservation. Notably, M. amblycephala lacked the teleost-specific il-17n but retained il-17bl, which is absent in many other teleost species. Following A. hydrophila challenge, il-17a/f1 was significantly upregulated in systemic immune organs such as the spleen and trunk kidney, while il-17c exhibited the strongest response in mucosal immune tissues like the gills, demonstrating distinct tissue-specific regulation. This study clarifies the evolutionary rule and immune function of Il-17 family in M. amblycephala, providing a theoretical basis for exploring the immune mechanism of bacterial diseases in fish.