5-HTR1D and 5-HTR2B regulated Cryptocaryon irritans-induced inflammatory response of large yellow croaker Larimichthys crocea.

In mammals, 5-hydroxytryptamine receptors (5-HTRs) are expressed on various immune cells, and regulate the host immune response. However, the immunomodulatory function of 5-HTR in fish still remains poorly understood. In this study, Lc_5-HTR1D and Lc_5-HTR2B genes were cloned from large yellow croaker (Larimichthys crocea), showing highly conserved structural characteristics with other vertebrates orthologs. Lc_5-HTR1D and Lc_5-HTR2B mRNAs exhibited high expression not only in the brain, but also in the immune-related tissues (gill and head kidney). Following Cryptocaryon irritans infection, the expressions of Lc_5-HTR1D mRNA were strikingly induced in the brain and immune-related tissues (gill, intestine, liver, head kidney and spleen), whereas Lc_5-HTR2B mRNAs showed notably up-regulation in the liver and head kidney (P < 0.05 or 0.01). Afterwards, 5-HTR1D antagonist (BRL15572) markedly inhibited the expression of TNF-α, IL-1β, CXCL8, and IL-17A/F3 mRNA in LPS or C. irritans protein-activated head kidney macrophages (HKMs) (P < 0.05). Conversely, 5-HTR2B antagonist (SB204741) notably enhanced TNF-α and IL-1β mRNA expression in LPS or C. irritans protein-activated HKMs (P < 0.05 or 0.01). Moreover, 5-HTR1D antagonist significantly inhibited the phagocytosis of C. irritans protein-activated HKMs, while 5-HTR2B antagonist distinctly promoted this process (P < 0.05). Finally, 5-HTR1D antagonist notably hindered the phosphorylation levels of JNK and IκB-α in C. irritans protein-activated HKMs (P < 0.05), whereas 5-HTR2B antagonist exerted no significant effects on p38, JNK and IκB-α phosphorylation levels in C. irritans protein-activated HKMs. The findings collectively demonstrated the differential and critical roles of Lc_5-HTR1D and Lc_5-HTR2B in regulating the inflammatory response and host defense mechanisms, and provides a new perspective for neuroimmune regulation of teleost.