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Non-specific cytotoxic cells (NCCs) are cytotoxic cell population found in innate immune system of teleost, playing crucial role in immune defense. Non-specific cytotoxic cell receptor protein 1 (NCCRP1) is responsible for recognizing target cells and activating NCCs. That said, since the studies regarding NCCs' role in fish during pathogen infection are few, it is necessary to conduct more comprehensive studies. In this study, we identified NCCRP1 from Trachinotus ovatus (ToNCCRP1). The open reading frame of ToNCCRP1 was found to be 702 bp, encoding a protein of 233 amino acids. Additionally, ToNCCRP1 contained a conserved F-box-associated domain and exhibited more than 61 % similarity to NCCRP1 in other fish species. Quantitative real-time PCR analysis showed that ToNCCRP1 mRNA was generally expressed in all tissues, with the highest level expressed in the liver. Furthermore, the expression of ToNCCRP1 was significantly upregulated following infection with Streptococcus iniae. In vitro experiments demonstrated that recombinant ToNCCRP1 possessed bacterial agglutination and binding capabilities, suggesting its antibacterial function. Additionally, we investigated the immune response of head kidney leukocytes (HKLs) to ToNCCRP1. The challenge experiments revealed that ToNCCRP1 played a role in the immune response by influencing the inflammatory response, regulating signaling pathways and apoptosis in HKLs. These findings suggest that NCCRP1 is involved in the immune defense against pathogenic infections in golden pompano, providing insights into the immune mechanisms of teleost. • ToNCCRP1 was identified from Trachinotus ovatus. • ToNCCRP1 expression level was induced during Streptococcus iniae infection. • ToNCCRP1 has antibacterial function in vitro. • ToNCCRP1was involved in the immune response in head kidney leukocytes of Trachinotus ovatus in vitro. [ABSTRACT FROM AUTHOR]

Heme oxygenase-1 (HO-1), an inducible rate-limiting metabolic enzyme, exerts critical immunomodulatory functions by potential anti-oxidant, anti-inflammatory, and anti-apoptotic activities. Although accumulative studies have focused on the immune functions of HO-1 in mammals, the roles in fish are poorly understood, and the reports on involvement in the defensive and immune response are very limited. In this study, On-HO-1 gene from Oreochromis niloticus was successfully cloned and identified, which contained an open reading frame (ORF) of 816 bp and coded for a protein of 271 amino acids. The On–HO–1 protein phylogenetically shared a high homology with HO-1 in other teleost fish (76.10%–98.89 %) and a lowly homology with HO-1 in mammals (38.98%–41.55 %). The expression levels of On-HO-1 were highest in the liver of healthy tilapias and sharply induced by Streptococcus agalactiae or Aeromonas hydrophila. Besides, On–HO–1 overexpression significantly increased non-specific immunological parameters in serum during bacterial infection, including LZM, SOD, CAT, ACP, and AKP. It also exerted anti-inflammatory and anti-apoptotic effects in response to the immune response of the infection with S. agalactiae or A. hydrophila by upregulating anti-inflammatory factors (IL-10 , TGF-β), autophagy factors (ATG6 , ATG8) and immune-related pathway factors (P65 , P38), and down-regulating pro-inflammatory factors (IL-1β , IL-6 , TNF-α), apoptotic factors (Caspase3 , Caspase9), pyroptosis factor (Caspase1), and inflammasome (NLRP3). These results suggested that On–HO–1 involved in immunomodulatory functions and host defense in Nile tilapia. • Heme oxygenase-1 (OnHO-1) was cloned from Oreochromis niloticus. • OnHO-1 was induced during Streptococcus agalactiae and Aeromonas hydrophila infection. • OnHO-1 overexpression could improve anti-oxidant activity, and enhance non-specific immunity. [ABSTRACT FROM AUTHOR]

High mobility group protein B2 (HMGB2) is an abundant chromatin-associated protein with pivotal roles in transcription, cell proliferation, differentiation, inflammation, and tumorigenesis. However, its immune function in Nile tilapia (Oreochromis niloticus) remains unclear. In this study, we identified a homologue of HMGB2 from Nile tilapia (On-HMGB2) and investigated its functions in the immune response against streptococcus infection. The open reading frame (ORF) of On-HMGB2 spans 642 bp, encoding 213 amino acids, and contains two conserved HMG domains. On-HMGB2 shares over 80 % homology with other fish species and 74%–76 % homology with mammals. On-HMGB2 was widely distributed in various tissues, with its highest transcript levels in the liver and the lowest in the intestine. Knockdown of On-HMGB2 promoted the inflammatory response in Nile tilapia, increased the bacterial load in the tissues, and led to elevated mortality in Nile tilapia following Streptococcus agalactiae infection. Taken together, On-HMGB2 significantly influences the immune system of Nile tilapia in response to streptococcus infection. • High mobility group protein B2 (On-HMGB2) was cloned from Oreochromis niloticus. • On-HMGB2 was knocked down by RNA interference. • HMGB2 protected O. niloticus against S. agalactiae infection in vivo. • HMGB2 is associated with an antimicrobial response with anti-inflammatory and anti-apoptotic effects. [ABSTRACT FROM AUTHOR]