title: TLR7/8 agonists activate a mild immune response in rabbits through TLR8 but not TLR7.
abstract: Toll-like receptors 7 (TLR7) and 8 (TLR8) recognize viral single-stranded RNA and small molecular weight agonists to activate anti-viral immune responses. TLR8s from different species have distinct ligand recognitions. For example, human TLR8 is responsive to ligand stimulation, but mouse and rat TLR8 are activated by small molecular weight agonists only in the presence of polyT-oligodeoxynucleotides. TLR7 and TLR8 have been reported to be absent and pseudogenized, respectively, in rabbit (Oryctolagus cuniculus). In this study, we detected the expression of rabbit (rab)TLR8 in immune-cell-associated tissues. Cell proliferation and cytokine expressions in rabbit splenocytes were induced by the TLR7/8 ligand but not by the TLR7 ligands, suggesting that rabTLR8 is functional but rabTLR7 is not. In rabbits, CL075, a TLR7/8 ligand, activated an antigen-specific antibody response, although one not as potent as aluminum salt or Freund's adjuvant. Nevertheless, CL075, alone or in combination with aluminum salt, generates fewer adverse effects than Freund's adjuvant at the injection sites. To further investigate the activation of rabTLR8, we cloned its cDNA. In cell-based assay, this rabTLR8 is activated by TLR7/8 ligand but not activated by TLR7 ligand. Upon stimulation the rabTLR8 had a lower activation compared to the activation of TLR8 from other species, except the mouse and rat TLR8s. Using different deletion and human-rabbit chimeric TLR8 expressing constructs, we showed that an extra peptide in the undefined region results in reduced activity of rabTLR8. These results provide a molecular basis for the mild activities of TLR7/8 ligands in rabbits, and suggest TLR7/8 agonists may provide safer immune stimuli in rabbits than in other non-rodent species.
authors.affiliation: Immunology Research Center, National Health Research Institutes, Miaoli 35053, Taiwan.
authors.forename: Chao-Yang
authors.initials: CY
authors.lastname: Lai
authors.affiliation: Immunology Research Center, National Health Research Institutes, Miaoli 35053, Taiwan.
authors.forename: Yi-Ling
authors.initials: YL
authors.lastname: Liu
authors.affiliation: National Institute of Infectious Diseases and Vaccinology, National Health Research Institutes, Miaoli 35053, Taiwan.
authors.forename: Guann-Yi
authors.initials: GY
authors.lastname: Yu
authors.affiliation: Graduate Institute of Basic Medical Science, China Medical University, Taichung 40402, Taiwan.
authors.forename: Ming-Chei
authors.initials: MC
authors.lastname: Maa
authors.affiliation: Department of Pharmacology, College of Medicine, National Cheng Kung University, Tainan 70101, Taiwan.
authors.forename: Tzeng-Horng
authors.initials: TH
authors.lastname: Leu
authors.affiliation: Shanghai Institute of Immunology, Institutes of Medical Sciences, Shanghai Jiaotong University School of Medicine, Shanghai 200025, PR China.
authors.forename: Congfeng
authors.initials: C
authors.lastname: Xu
authors.affiliation: Department of Immunology, School of Basic Medicine, Peking Union Medical College, Beijing 100005, PR China.
authors.forename: Yunping
authors.initials: Y
authors.lastname: Luo
authors.affiliation: School of Medicine, University of Nankai, Tianjin 300071, PR China.
authors.forename: Rong
authors.initials: R
authors.lastname: Xiang
authors.affiliation: Immunology Research Center, National Health Research Institutes, Miaoli 35053, Taiwan; Program in Environmental and Occupational Medicine, Kaohsiung Medical University, Kaohsiung 80708, Taiwan. Electronic address: thchuang@nhri.org.tw.
authors.forename: Tsung-Hsien
authors.initials: TH
authors.lastname: Chuang
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000917:Antibody Formation; D049109:Cell Proliferation; D002478:Cells, Cultured; D016207:Cytokines / Q000276:immunology; D057809:HEK293 Cells; D006801:Humans; D008024:Ligands; D008969:Molecular Sequence Data; D017434:Protein Structure, Tertiary; D011817:Rabbits; D013154:Spleen / Q000166:cytology / Q000276:immunology*; D051199:Toll-Like Receptor 7 / Q000819:agonists* / Q000276:immunology*; D051200:Toll-Like Receptor 8 / Q000819:agonists* / Q000276:immunology*
chemical_list: D016207:Cytokines; D008024:Ligands; D051199:Toll-Like Receptor 7; D051200:Toll-Like Receptor 8
keywords: Adjuvant activity; Innate immunity; Pattern recognition receptor; Species-specific recognition; Toll-like receptor