β-globin mediates antimicrobial defense and inflammatory regulation in common carp (Cyprinus carpio).

β-globin is a core subunit of hemoglobin, playing an indispensable role in oxygen transport, but its immunological functions have been less extensively characterized. In this study, we identified and characterized the β-globin gene from Cyprinus carpio (designated Ccβ-globin), with a specific focus on its transcriptional response to pathogenic stimuli and antimicrobial activity against pathogens. The open reading frame (ORF) of Ccβ-globin consists of a 447 bp nucleotide sequence, encoding a 148 amino acids polypeptide. Quantitative analysis revealed that Ccβ-globin is constitutively expressed across multiple tissues, with the highest transcription levels detected in the heart and blood. Moreover, Ccβ-globin transcription was significantly upregulated in response to stimulation with lipopolysaccharide (LPS) and Aeromonas hydrophila. Recombinant Ccβ-globin (rCcβ-globin) exhibited concentration-dependent binding affinity for LPS and exerted direct binding, agglutination, and growth inhibitory effects against six representative pathogens. In an in vitro model using primary head kidney leukocytes of common carp infected with A. hydrophila, Ccβ-globin treatment modulated the expression of key inflammatory cytokines including IL-1β, IL-6, and IL-10. Additionally, in vivo administration of rCcβ-globin via intraperitoneal injection ameliorated inflammatory responses, alleviated pathogen-induced inflammatory damage, and enhanced the immune defense capability of the host. Collectively, our findings demonstrate that Ccβ-globin plays a pivotal role in regulating the innate immune response of common carp, thereby providing novel insights into the evolutionary dynamics and functional diversification of hemoglobin superfamily proteins in teleosts.