Poly(I:C) induces antiviral immune responses in Japanese flounder (Paralichthys olivaceus) that require TLR3 and MDA5 and is negatively regulated by Myd88.
Polyinosinic:polycytidylic acid (poly(I:C)) is a ligand of toll-like receptor (TLR) 3 that has been used as an immunostimulant in humans and mice against viral diseases based on its ability to enhance innate and adapt immunity. Antiviral effect of poly(I:C) has also been observed in teleost, however, the underling mechanism is not clear. In this study, we investigated the potential and signaling mechanism of poly(I:C) as an antiviral agent in a model of Japanese flounder (Paralichthys olivaceus) infected with megalocytivirus. We found that poly(I:C) exhibited strong antiviral activity and enhanced activation of head kidney macrophages and peripheral blood leukocytes. In vivo studies showed that (i) TLR3 as well as MDA5 knockdown reduced poly(I:C)-mediated immune response and antiviral activity to significant extents; (ii) when Myd88 was overexpressed in flounder, poly(I:C)-mediated antiviral activity was significantly decreased; (iii) when Myd88 was inactivated, the antiviral effect of poly(I:C) was significantly increased. Cellular study showed that (i) the NF-κB activity induced by poly(I:C) was upregulated in Myd88-overexpressing cells and unaffected in Myd88-inactivated cells; (ii) Myd88 overexpression inhibited and upregulated the expression of poly(I:C)-induced antiviral genes and inflammatory genes respectively; (iii) Myd88 inactivation enhanced the expression of the antiviral genes induced by poly(I:C). Taken together, these results indicate that poly(I:C) is an immunostimulant with antiviral potential, and that the immune response of poly(I:C) requires TLR3 and MDA5 and is negatively regulated by Myd88 in a manner not involving NK-κB. These results provide insights to the working mechanism of poly(I:C), TLR3, and Myd88 in fish.
Key Laboratory of Experimental Marine Biology, Institute of Oceanology, Chinese Academy of Sciences, Qingdao, China.
Zhi-xia
ZX
Zhou
Key Laboratory of Experimental Marine Biology, Institute of Oceanology, Chinese Academy of Sciences, Qingdao, China; University of Chinese Academy of Sciences, Beijing, China.
Bao-cun
BC
Zhang
Key Laboratory of Experimental Marine Biology, Institute of Oceanology, Chinese Academy of Sciences, Qingdao, China; Collaborative Innovation Center of Deep Sea Biology, Zhejiang University, Hangzhou, China.
Li
L
Sun
D000818:Animals; D053487:DEAD-box RNA Helicases / Q000235:genetics / Q000276:immunology*; D004266:DNA Virus Infections / Q000235:genetics / Q000276:immunology / Q000662:veterinary; D005393:Fish Diseases / Q000235:genetics / Q000276:immunology; D029941:Fish Proteins / Q000235:genetics / Q000276:immunology*; D005432:Flounder / Q000235:genetics / Q000276:immunology*; D007497:Iridoviridae / Q000235:genetics / Q000276:immunology; D051379:Mice; D053594:Myeloid Differentiation Factor 88 / Q000235:genetics / Q000276:immunology*; D011070:Poly I-C / Q000494:pharmacology*; D051196:Toll-Like Receptor 3 / Q000235:genetics / Q000276:immunology*
D029941:Fish Proteins; D053594:Myeloid Differentiation Factor 88; D051196:Toll-Like Receptor 3; D053487:DEAD-box RNA Helicases; D011070:Poly I-C