![]() ĭo V-type TLRs in amphioxus and sea urchin serve as sheer PRRs as they do in vertebrates?.ĭo P-type TLRs in amphioxus and sea urchin act as cytokine receptors as they do in Drosophila?.Because cephalochordates and echinoderms represent the oldest extant lineages for the chordate phylum and deuterostome superphylum, respectively, these discoveries imply that the ancestors of vertebrates may have had a much more complex and powerful TLR system. Amphioxus has both P-type and V-type TLRs, and the V-type TLR repertoire has undergone a large expansion, so the loss of P-type TLRs should occur after the divergence of amphioxus and vertebrate. Thus, the amphioxus TLR family is not as diversified as that of sea urchin. The function of the only V-type TLR (dToll9) in Drosophila has not been fully determined, although it is thought to be part of constitutively activated host defense ( Ooi et al., 2002).Ĭompared to protostomes and vertebrates, chordate invertebrates possess greatly expanded TLR repertoires because the echinoderm sea urchin has 222 TLRs whereas cephalochordate amphioxus has at least 39 TLRs ( Hibino et al., 2006 Huang et al., 2008). Vertebrate TLRs all are V-type TLRs and serve as PRRs in immunity, without any developmental function, whereas some Drosophila P-type TLRs serve as cytokine receptors for Spätzle and participate in embryonic development as well as immunity ( Parker et al., 2001 Bilak et al., 2003 Gangloff et al., 2003). Drosophila melanogaster has eight P-type TLRs but only one V-type TLR ( Ooi et al., 2002). The TLR11 family contains TLR11-13 and TLR21-23 subfamilies, but little is known about their function except that mouse TLR11 responds to profilin and nonpathogenic bacteria ( Roach et al., 2005). ![]() ![]() The TLR1, TLR3, TLR4, TLR5, and TLR7 families recognize lipopeptides, dsRNA, LPS, flagellin, and nucleic acid, respectively ( Roach et al., 2005). Vertebrate TLRs can be classified into six major families and each family leads to a distinct immune response by recognizing a specific class of PAMPs. Jawed vertebrates have approximately 12 TLRs, and all of them are typical V-type TLRs ( Roach et al., 2005). The Protein Architecture of V-Type and P-Type TLRs in Amphioxus.Īlso shown is the specific localization of bbtTLR1 in the pro-MHC region. ![]()
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