The scavenger receptor CD36 protects Nile tilapia (Oreochromis niloticus) against Streptococcus agalactiae infection and promotes the expression of inflammatory factors

To explore the role of CD36 (Cluster of Differentiation 36) in the antimicrobial immunity of Nile tilapia, the PCR was used to clone the CD36 gene (named OnCD36). The results showed that the ORF was 1407 bp, encoding 468 amino acids. Multiple sequence alignment revealed that OnCD36 was conserved among species. Subcellular localization proved that OnCD36 was distributed in the cell membrane. RT-PCR analysis presented that OnCD36 gene was expressed in all tissues of healthy tilapia, and the expression of OnCD36 gene was higher in immune tissues such as the head kidney, intestine, skin. After inactivated S. agalactiae and Poly I: C stimulated, the expression of OnCD36 in blood, head kidney, spleen and thymus showed a temporal expression. In vitro exper-iments showed that OnCD36 extracellular protein could bind to bacteria through the surface structure of bacteria LPS, LTA, PGN. In vivo experiments demonstrated that OnCD36 overexpression before S. agalactiae challenge, which could effectively reduce the bacterial load in the spleen and liver tissues, reduce the injury of immune tissues or organs to varying degrees. Moreover, the overexpression of CD36 in the activity of AKP, ACP, SOD in OnCD36 experimental group was significantly higher than that in the control group. OnCD36 also reduces inflammation and protects tilapia from S. agalactiae infection by increasing the expression of anti-inflammatory factors IL-10 and TGF-beta and decreasing the expression of pro-inflammatory factors IL-6 and TNF-alpha. In conclusion, these studies indicate that OnCD36 may play a vital role in pathogen control and immune response in tilapia. However, the pathway mechanism involved in OnCD36 regulating the expression of inflammatory factors needs to be further studied.