title: Origin of Toll-like receptor-mediated innate immunity.
abstract: Toll-related receptors (TLR) have been found in four animal phyla: Nematoda, Arthropoda, Echinodermata, and Chordata. No TLR has been identified thus far in acoelomates. TLR genes play a pivotal role in the innate immunity in both fruit fly and mammals. The prevailing view is that TLR-mediated immunity is ancient. The two pseudocoelomate TLRs, one each from Caenorhabditis elegans and Strongyloides stercoralis, were distinct from the coelomate ones. Further, the only TLR gene (Tol-1) in Ca. elegans did not appear to play a role in innate immunity. We argue that TLR-mediated innate immunity developed only in the coelomates, after they split from pseudocoelomates and acoelomates. We hypothesize that the function of TLR-mediated immunity is to prevent microbial infection in the body cavity present only in the coelomates. Phylogenetic analysis showed that almost all arthropod TLRs form a separate cluster from the mammalian counterparts. We further hypothesize that TLR-mediated immunity developed independently in the protostomia and deuterostomia coelomates.
authors.affiliation: Yale University School of Medicine, Epidemiology and Public Health, 60 College Street, New Haven, CT 06520, USA.
authors.forename: Stefan M
authors.initials: SM
authors.lastname: Kanzok
authors.forename: Ngo T
authors.initials: NT
authors.lastname: Hoa
authors.forename: Mariangela
authors.initials: M
authors.lastname: Bonizzoni
authors.forename: Coralia
authors.initials: C
authors.lastname: Luna
authors.forename: Yaming
authors.initials: Y
authors.lastname: Huang
authors.forename: Anna R
authors.initials: AR
authors.lastname: Malacrida
authors.forename: Liangbiao
authors.initials: L
authors.lastname: Zheng
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D016000:Cluster Analysis; D004247:DNA; D005091:Exons; D007113:Immunity, Innate / Q000502:physiology*; D007438:Introns; D008562:Membrane Glycoproteins / Q000737:chemistry / Q000502:physiology*; D008969:Molecular Sequence Data; D011956:Receptors, Cell Surface / Q000737:chemistry / Q000502:physiology*; D051193:Toll-Like Receptors
chemical_list: D008562:Membrane Glycoproteins; D011956:Receptors, Cell Surface; D051193:Toll-Like Receptors; D004247:DNA