title: Antibodies directed against O-acetylated sialoglycoconjugates accelerate complement activation in Leishmania donovani promastigotes.
abstract: BACKGROUND
  An enhanced presence of 9-O-acetylated sialoglycoconjugates (9-O-AcSGs) triggers the alternate pathway (AP) in Indian visceral leishmaniasis (VL). Antibodies directed against these epitopes are present in high titers. The biological relevance of these antibodies, with regard to activation of the classical pathway (CP), was investigated.
  
  
  METHODS
  Complement activators were affinity purified, complement activation via the CP, AP, and lectin-mediated complement pathway was measured by use of an anti-C3 radio-binding assay, and the number of C3 molecules was quantitated by Scatchard analysis. Cell death induced via the complement pathways was measured by use of MTT (tetrazolium salt 3- [4, 5-dimethylthiazol-2-yl] -2, 5-diphenyltetrazolium bromide) assay, and uptake of propidium iodide (PI) was measured by flow cytometry.
  
  
  RESULTS
  Anti-O-AcSGs from both healthy donors and patients with VL elicited C3 deposition as early as 3 min, which triggered parasite lysis, as demonstrated by use of MTT assay and corroborated by the high rate of uptake of PI. Analysis of complement activation by mannan-binding lectin and C-reactive protein demonstrated their negligible contribution during the 3-min time frame.
  
  
  CONCLUSIONS
  Anti-O-AcSGs were identified as an important source of CP activation under normal physiological conditions, suggesting that they play a role in conferring host protection against parasite infection.
authors.affiliation: Immunobiology Division, Indian Institute of Chemical Biology, 4 Raja S.C. Mullick Road, Jadavpur, Kolkata 700-032, India.
authors.forename: Sumi
authors.initials: S
authors.lastname: Bandyopadhyay
authors.forename: Mitali
authors.initials: M
authors.lastname: Chatterjee
authors.forename: Tanusree
authors.initials: T
authors.lastname: Das
authors.forename: Suman
authors.initials: S
authors.lastname: Bandyopadhyay
authors.forename: Shyam
authors.initials: S
authors.lastname: Sundar
authors.forename: Chitra
authors.initials: C
authors.lastname: Mandal
mesh_terms: D000818:Animals; D000913:Antibodies, Protozoan / Q000302:isolation & purification / Q000494:pharmacology*; D003167:Complement Activation / Q000187:drug effects*; D003176:Complement C3 / Q000032:analysis / Q000276:immunology*; D003170:Complement Pathway, Alternative / Q000187:drug effects; D003171:Complement Pathway, Classical / Q000187:drug effects; D004306:Dose-Response Relationship, Immunologic; D006001:Glycoconjugates / Q000276:immunology*; D006801:Humans; D007893:Leishmania donovani / Q000187:drug effects / Q000276:immunology*; D007898:Leishmaniasis, Visceral / Q000097:blood / Q000276:immunology*; D013997:Time Factors
chemical_list: D000913:Antibodies, Protozoan; D003176:Complement C3; D006001:Glycoconjugates