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The Central Leucine-Rich Repeat Region of Chicken TLR16 Dictates Unique Ligand Specificity and Species-Specific Interaction with TLR2¹

Department of Infectious Diseases and Immunology, Utrecht University, Utrecht, The Netherlands

The ligand specificity of human TLR (hTLR) 2 is determined through the formation of functional heterodimers with either hTLR1 or hTLR6. The chicken carries two TLR (chTLR) 2 isoforms, type 1 and type 2 (chTLR2t1 and chTLR2t2), and one putative TLR1/6/10 homologue (chTLR16) of unknown function. In this study, we report that transfection of HeLa cells with the various chicken receptors yields potent NF-B activation for the receptor combination of chTLR2t2 and chTLR16 only. The sensitivity of this complex was strongly enhanced by human CD14. The functional chTLR16/chTLR2t2 complex responded toward both the hTLR2/6-specific diacylated peptide S-(2,3-bispalmitoyloxypropyl)-Cys-Gly-Asp-Pro-Lys-His-Pro-Lys-Ser-Phe (FSL-1) and the hTLR2/1 specific triacylated peptide tripalmitoyl-S-(bis(palmitoyloxy)propyl)-Cys-Ser-(Lys)₃-Lys (Pam₃CSK₄), indicating that chTLR16 covers the functions of both mammalian TLR1 and TLR6. Dissection of the species specificity of TLR2 and its coreceptors showed functional chTLR16 complex formation with chTLR2t2 but not hTLR2. Conversely, chTLR2t2 did not function in combination with hTLR1 or hTLR6. The use of constructed chimeric receptors in which the defined domains of chTLR16 and hTLR1 or hTLR6 had been exchanged revealed that the transfer of leucine-rich repeats (LRR) 6–16 of chTLR16 into hTLR6 was sufficient to confer dual ligand specificity to the human receptor and to establish species-specific interaction with chTLR2t2. Collectively, our data indicate that diversification of the central LRR region of the TLR2 coreceptors during evolution has put constraints on both their ligand specificity and their ability to form functional complexes with TLR2.

The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

¹ This work received financial support from the "Adaptation and Resistance Initiative" and ZonMw Grant 912-03-007.

² Address correspondence and reprint requests to Dr. Jos P. M. van Putten, Department of Infectious Diseases and Immunology Utrecht University, Yalelaan 1, Utrecht, The Netherlands. E-mail address: j.vanputten{at}vet.uu.nl

³ Abbreviations used in this paper: LRR, leucine-rich repeat; chTLR, chicken TLR; ChTLR2t1/2, ChTLR2 isoform type 1 or type 2; FSL-1, S-(2,3-bispalmitoyloxypropyl)-Cys-Gly-Asp-Pro-Lys-His-Pro-Lys-Ser-Phe; hTLR, human TLR; RLU, relative light unit; Pam₃CSK₄, tripalmitoyl-S-(bis(palmitoyloxy)propyl)-Cys-Ser-(Lys)₃-Lys; TIR, Toll/IL-1 receptor; TM, transmembrane.

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