Role of crustacean female sex hormone in regulating immune response in the mud crab, Scylla paramamosain

Crustacean female sex hormone (CFSH) is responsible for sexual differentiation in crustaceans. The CFSH exhibited an interleukin-17 domain homologous to vertebrate IL-17, a family of inflammatory cytokines that play vital roles in immune defense. However, the immunoregulation of CFSH in crustaceans is a mystery. Therefore, this study aimed to investigate the immune regulatory roles of CFSH and CFSHR in the mud crab Scylla paramamosain. This study's immunofluorescence result revealed that Sp-CFSHR was highly expressed in granulocytes and semi-granulocytes but had moderate expression in hyalinocytes. The expression level of Sp-CFSH transcript in eyestalk ganglia and Sp-CFSHR in hemocytes were significantly up-regulated by the Poly (I:C) stimulation but significantly down-regulated in response to the lipopolysaccharide (LPS) stimulation. In our study, in vitro experiment exhibited that the nuclear transcription factors NF-kappa B signaling molecules (Sp-Dorsal and Sp-Relish), Sp-STAT, apoptosis-related gene Sp-IAP, and phagocytosis related gene (Sp-Rab5) expressions were significantly increased in hemocytes by recombinant CFSH (rCFSH) in vitro, but the pro-inflammatory cytokine gene (Sp-IL-16) expression was significantly suppressed. Finally, the rCFSH injection significantly up-regulated Sp-Dorsal, SpRelish, Sp-IAP, Sp-Caspase, Sp-ALF2, and C-type lectin (Sp-CTL-B) expressions in hemocytes as well as enhanced the bacterial clearance of the mud crab. In conclusion, our results suggested that CFSH may be a counterpart of vertebrate IL-17 in crustaceans that can enhance innate immunity to defense against Vibrionaceae infection via the NF-kappa B and/or JAK-STAT signaling pathways. This study provides the first evidence that CFSH is involved in the immunoregulation in crustaceans and enriches the insight of neuroendocrine-immune regulatory system, which providing new ideas for disease prevention in the mud crab industry.