Molecular evidence for the involvement of RORα and RORγ in immune response in teleost

In mammals, retinoid-related orphan receptors (ROR) consist of three members as RORα, RORβ and RORγ. It is well known that RORα plays a critical role in cerebellum development while RORγt directs T helper 17 (Th17) cell differentiation. So far, the knowledge on fish ROR family is limited as only zebrafish ROR family members have been characterized, showing that they play roles in embryonic and cerebellar development. In this study, we have cloned two paralogues for RORα (RORα1 and RORα2) and RORγ (RORγ1 and RORγ2) from grass carp (Ctenopharyngodon idellus). Phylogenetic analysis showed that grass carp RORα and RORγ were grouped in the clade of zebrafish RORα and RORγ, respectively. Real-time RT-PCR assay revealed that these four ROR transcripts exhibited similar expression patterns, in particular the high levels in pituitary, brain and some immune-related tissues, suggesting that all of them may play a role in endocrine and immune system of teleost. To explore the immune roles of grass carp RORα and RORγ, their expression was detected in periphery blood lymphocytes (PBLs) challenged by immune stimuli. Results showed that both RORα and RORγ mRNA levels were up-regulated by PHA but not LPS in PBLs, suggesting that their expression may be subject to different immune processes. In the same cell model, poly I:C stimulation induced RORγ1/2 but not RORα1/2 expression, pointing to the different roles of grass carp RORα and RORγ in immune response. Consistently, bacterial challenge significantly up-regulated the expression of these four ROR genes in spleen, headkidney and thymus. These results not only contribute to elucidate the roles of ROR in fish immunity but also facilitate to further clarify the existence of Th17-like cells in fish.