title: Cloning and characterization of a gene encoding an immunoglobulin-binding receptor on the cell surface of some members of the family Trypanosomatidae.
abstract: Several members of the Trypanosomatidae family, when freshly isolated from their mammalian hosts, have immunoglobulins adsorbed to their cell surfaces. However, a significant portion of these antibody molecules is not parasite specific, i.e., the immunoglobulins are bound to the parasite's cell surface molecules via noncognitive interactions. It has been proposed that this noncognitive adsorption of immunoglobulins to the parasite is mediated by an Fc-like receptor present in several members of the Trypanosomatidae family. However, the molecular identification of this receptor has never been defined. Here, we describe the cloning of a gene encoding a protein that might represent this molecule. The gene, named Lmsp1, was cloned by screening a Leishmania major cDNA expression library using a rabbit antiserum. Lmsp1 is present in both Leishmania and Trypanosoma and is expressed in all developmental stages of these parasites. The predicted protein has a molecular mass of 16.6 kDa and contains an RGD sequence starting at residue 104 and three cysteine residues at positions 55, 74, and 116. The purified recombinant protein strongly binds to normal immunoglobulins of various animal species (humans, rabbits, sheep, goats, guinea pigs, donkeys, rats, and mice) and the binding to human immunoglobulins appears to be immunoglobulin G (IgG) and IgM isotype specific. Moreover, Lmsp1 binds to both purified Fc and Fab fragments of IgG from both humans and rabbits. The mapping of the Lmsp1 epitopes that bind human IgG revealed that different sequences of the molecule bind to Fc or Fab. In addition, fluorescence-activated cell sorter analyses with a specific rabbit anti-Lmsp1 antiserum showed that Lmsp1 is associated with the parasite's cell surface. Finally, inhibition experiments point to an active role of this molecule in the immunoglobulin-mediated attachment and penetration of Trypanosoma cruzi in its macrophage host cells, thus suggesting that Lmsp1 is a putative Trypanosomatidae immunoglobulin receptor.
authors.affiliation: Infectious Disease Research Institute, Seattle, Washington, USA. acampos@forsyth.org
authors.forename: Antonio
authors.initials: A
authors.lastname: Campos-Neto
authors.forename: Isabelle
authors.initials: I
authors.lastname: Suffia
authors.forename: Karen A
authors.initials: KA
authors.lastname: Cavassani
authors.forename: Shyian
authors.initials: S
authors.lastname: Jen
authors.forename: Kay
authors.initials: K
authors.lastname: Greeson
authors.forename: Pamela
authors.initials: P
authors.lastname: Ovendale
authors.forename: João S
authors.initials: JS
authors.lastname: Silva
authors.forename: Steven G
authors.initials: SG
authors.lastname: Reed
authors.forename: Yasir A W
authors.initials: YA
authors.lastname: Skeiky
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D001665:Binding Sites / Q000235:genetics; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000235:genetics; D016054:DNA, Protozoan / Q000235:genetics; D017125:Genes, Protozoan; D006801:Humans; D007136:Immunoglobulins / Q000378:metabolism*; D066298:In Vitro Techniques; D018320:Leishmania major / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D051379:Mice; D008969:Molecular Sequence Data; D008970:Molecular Weight; D010449:Peptide Mapping; D011485:Protein Binding; D015800:Protozoan Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D011817:Rabbits; D011956:Receptors, Cell Surface / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D011971:Receptors, Immunologic / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D014345:Trypanosoma / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D014351:Trypanosomatina / Q000235:genetics* / Q000276:immunology / Q000378:metabolism
chemical_list: D018076:DNA, Complementary; D016054:DNA, Protozoan; D007136:Immunoglobulins; D015800:Protozoan Proteins; D011956:Receptors, Cell Surface; D011971:Receptors, Immunologic