Identification of scavenger receptor (LmSRA3) gene and its immune response to Aeromonas veronii in Lateolabrax maculatus.

Scavenger receptors (SRs) serve as essential pattern recognition receptors in the innate immune system, playing multiple roles in the immunity of fish. They contribute to defense mechanisms against pathogenic infections through various pathways. However, research on the functions of SRs in the immune response of Spotted sea bass remains limited. Here, the LmSRA3 gene was cloned and identified from Spotted sea bass, and a bioinformatic analysis of the sequence was conducted. This analysis revealed that the open reading frame of LmSRA3 spans 1821 bp and encodes 606 amino acids. The estimated molecular mass of this protein is 66.62 kDa, accompanied by isoelectric point of 6.06. It contains a collagen domain, a low-complexity structure, and two coiled-coils regions. Multiple sequence comparisons and phylogenetic analyses demonstrated that the LmSRA3 sequence is notably conserved among fish species. Furthermore, qPCR analysis showed that the LmSRA3 gene is expressed in all examined tissues, with the highest expression in the intestine. In the head kidney, spleen, blood, and intestine after infection with A. veronii, the expression levels of the LmSRA3 gene generally exhibited a pattern of first increasing followed by decreasing, suggesting that LmSRA3 may be involved in the immune response to A. veronii infection through multiple pathways. Subcellular localization experiments revealed that LmSRA3 is predominantly distributed in the cytoplasm. Additionally, results from the enzyme-linked immunosorbent assay indicated the binding capacity of LmSRA3 to A. veronii is not significant. Furthermore, interference or overexpression of LmSRA3 significantly affected the expression of RelA, MyD88, TNFR1, and IL-1β. These results emphasize that LmSRA3 may play a crucial role in the innate immune response of Spotted sea bass and provides insights into the mechanism by which SRs are in the antibacterial immunity of this species.