IL8 of Takifugu rubripes is a chemokine that interacts with peripheral blood leukocytes and promotes antibacterial defense

PoCXCL8, a teleost chemokine, exerts direct bactericidal, chemotactic/phagocytic, and NETs releasing properties, promoting host anti-bacterial immunity

As an important CXC chemokine, CXCL8 plays pleiotropic roles in immunological response. In teleost, CXCL8 is involved in cell migration and bacterial invasion. However, the immune antibacterial function of CXCL8 in Japanese flounder (Paralichthys olivaceus) (PoCXCL8) is largely scarce. In this research, we investigated the antibacterial property and leukocyte activation of PoCXCL8. PoCXCL8 consists of 100 amino acid residues, with a conserved chemokine CXC domain. PoCXCL8 was expressed in various tissues, with the highest level in liver and the lowest level in muscle, and sharply induced by V. harveyi or E. tarda in liver, spleen, and head kidney. In vitro, the recombinant PoCXCL8 (rPoCXCL8) could bind to Bacillus subtilis, Edwardsiella tarda, Escherichia coli, Pseudomonas fluorescens, Vibrio anguillarum, Vibrio harveyi, Staphylococcus aureus, and Micrococcus luteus, affect the growth of E. coli, E. tarda, M. luteus, and P. fluorescens, and have a direct bactericidal effect on E. coli and E. tarda. Moreover, rPoCXCL8 was able to bind the outer membranal protein rPilA of E. tarda. In addition, rPoCXCL8 could bind to PBLs, activating the PBLs activity including chemotaxis, proliferation, phagocytosis, reactive oxygen species, acid phosphatase activity. At same time, rPoCXCL8 could induce neutrophil to generate neutrophil extracellular traps (NETs) and promote the expression of inflammatory genes including IL-1β, IL6, MMP13, TNF-α, and NF-κB. In flounder, the presence of rPoCXCL8 could enhance the in vivo resistance to E. tarda in liver, spleen, and head kidney. Moreover, the PoCXCL8-deficient could attenuate the fish defense against E. tarda infection in in spleen and head kidney. In conclusion, these results provided new insights into the antibacterial properties of CXCL8 in P. olivaceus.

PoIL8-L, a teleost interleukin-8 like, enhances leukocyte cellular vitality and host defense against bacterial infections in Japanese flounder (Paralichthys olivaceus)

Interleukin-8 (IL-8), a CXC chemokine, exerts pivotal effect on cell migration, inflammatory response, and immune regulation. In this study, we examined the immunological characteristics of an IL-8 like homologue (PoIL8-L) in Japanese flounder (Paralichthys olivaceus). PoIL8-L contains a conserved chemokine CXC domain and 105 amino acid residues. PoIL8-L expression in tissues was constitutive, and significantly regulated by V. havieri or E. tarda infection. In vitro, rPoIL8-L could bind to eight tested bacteria, exhibited bacteriostatic and bactericidal effects against certain bacteria, and could bind to the targeted bacterial Ⅳ pilin protein rPilA of E. tarda. Furthermore, rPoIL8-L could attach to peripheral blood leukocytes, and enhance their immune genes expression, respiratory burst, chemotaxis, proliferation, acid phosphatase activity, and phagocytic activity. Additionally, rPoIL8-L induce neutrophils to extrude neutrophil extracellular traps. In vivo, rPoIL8-L could promote host resistance to E. tarda infection. In summary, these findings provide fresh perspectives on the immunological antibacterial properties of IL-8 in teleost.

Teleost-specific TLR23 in Takifugu rubripes recruits MyD88 to trigger ERK pathway and promotes antibacterial defense

Takifugu rubripes is a highly valued cultured fish in Asia, while pathogen infections can result in severe diseases and lead to substantial economic losses. Toll-like receptors (TLRs), as pattern recognition receptors, play a crucial role on recognition pathogens and initiation innate immune response. However, the immunological properties of teleost-specific TLR23 remain largely unknown. In this study, we investigated the biological functions of TLR23 (TrTLR23) from T. rubripes, found that TrTLR23 existed in various organs. Following bacterial pathogen challenge, the expression levels of TrTLR23 were significantly increased in immune related organs. TrTLR23 located on the cellular membrane and specifically recognized pathogenic microorganism. Co-immunoprecipitation and antibody blocking analysis revealed that TrTLR23 recruited myeloid differentiation primary response protein (MyD88), thereby mediating the activation of the ERK signaling pathway. Furthermore, in vivo showed that, when TrTLR23 is overexpressed in T. rubripes, bacterial replication in fish tissues is significantly inhibited. Consistently, when TrTLR23 expression in T. rubripes is knocked down, bacterial replication is significantly enhanced. In conclusion, these findings suggested that TrTLR23 played a critical role on mediation TLR23-MyD88-ERK axis against bacterial infection. This study revealed that TLR23 involved in the innate immune mechanism, and provided the foundation for development disease control strategies in teleost.

CsIL-20, a tongue sole interleukin-20, negatively mediates leucocyte activity and antibacterial defense

Interleukin-20 (IL-20), as an essential member of IL-10 family, plays vital roles in mammalian immunological response such as antimicrobial, inflammation, hematopoiesis, and immune diseases. In teleost, the study about immune antimicrobial function of IL-20 is largely scarce. In this article, we revealed the expression profiles and the immunological functions of the IL-20 (CsIL-20) in tongue sole Cynoglossus semilaevis. CsIL-20 is composed of 183 amino acid residues, with seven cysteine residues and a typical IL-10 domain which comprises six α-helices and two β-sheets, and shares 34.4-71.2 % identities with other teleost IL-20. CsIL-20 was constitutively expressed in a variety of tissues and regulated by bacterial invasion, and the recombinant CsIL-20 (rCsIL-20) could bind to different bacteria. In vitro rCsIL-20 could interact with the membrane of peripheral blood leukocytes (PBLs), leading to the attenuation of reactive oxygen species (ROS) production and acid phosphatase activity in PBLs. In line with In vitro results, In vivo rCsIL-20 could obviously suppressed the host immune against bacterial infection. Furthermore, knockdown of CsIL-20 in vivo could markedly enhance the host antibacterial immunity. Collectively, these observations offer new insights into the negative effect of CsIL-20 on antibacterial immunity.