Molecular and functional characterization of IL-1 receptor type 2 in grass carp: A potent inhibitor of IL-1β signaling in head kidney leukocytes

Abstract

IL-1 receptor type 2 (IL-1R2) is known as one of natural IL-1β singling inhibitors in mammals. However, the functional role of IL-1R2 in fish remains largely unknown. In this study, grass carp (Ctenopharyngodon idellus) IL-1R2 (gcIL-1R2) was identified and functionally characterized. Similar to its fish homologs, the deduced protein of gcIL-1R2 possessed two Ig-like domains in its extracellular region but lacked an intracellular signaling domain. The involvement of gcIL-1R2 in immune response was demonstrated by investigating its expression profiles in head kidney and head kidney leukocytes (HKLs) following in vivo bacterial infection and in vitro LPS treatment, respectively. Moreover, recombinant grass carp IL-1β (rgcIL-1β) was able to stimulate gcIL-1R2 mRNA expression with a rapid kinetics. This stimulation was possibly dependent on p38, JNK, p42/44 and NF-κB pathways in grass carp HKLs, revealing a new regulatory point of IL-1β signaling at receptor level in fish. Furthermore, recombinant protein of the gcIL-1R2 extracellular region (rgcIL-1R2) was demonstrated to interact with rgcIL-1β by using ELISA, elucidating the binding specificity of gcIL-1R2. Importantly, the stimulatory effect of rgcIL-1β on its own mRNA expression was blocked by rgcIL-1R2 in a dose-dependent manner in grass carp HKLs, providing the evidence for a functional role of IL-1R2 in IL-1β signaling in teleost. These findings suggested that teleost IL-1R2 may serve as a local naturally occurring inhibitor involving in IL-1β signaling as seen in mammals.