title: Over-expressed IgG2 antibodies against O-acetylated sialoglycoconjugates incapable of proper effector functioning in childhood acute lymphoblastic leukemia.
abstract: Earlier studies have demonstrated an over-expression of 9-O-acetylated sialoglycoconjugates (9-OAcSGs) on lymphoblasts, concomitant with high titers of anti-9-OAcSGs in childhood acute lymphoblastic leukemia (ALL). The present study was aimed to evaluate whether this high induction of anti-9-OAcSGs at disease presentation contributes toward immune surveillance. Accordingly, anti-9-OAcSGs were affinity purified from sera of ALL patients and normal individuals, and their specificity toward the glycotope having terminal 9-O-acetylated sialic acid-linked subterminal N-acetyl galactosamine (GalNAc) in alpha2-6 manner (9-OAcSAalpha2-6GalNAc) was established by hemagglutination assay, flow cytometry and confocal microscopy. Subclass distribution of anti-9-OAcSGs revealed a predominance of IgG2 in ALL. Analysis of glycosylation of anti-9-OAcSGs purified from sera of ALL patients (IgG(ALL)) and normal individuals (IgG(N)) by digoxigenin glycan enzyme assay, fluorimetric estimation, gas-liquid chromatography and lectin-binding assays demonstrated that disease-specific antibodies differ in content and nature as compared with normal controls. Enhanced amount of 9-OAcSA-specific IgG2 induced in ALL was unable to trigger activation of FcgammaR, the complement cascade and cell-mediated cytotoxicity, although its glycotope-binding ability remains unaffected. Interestingly, only IgG1N emerged as the potent mediator of cell-mediated cytotoxicity, complement fixation and activator of effector cells through FcgammaR. In ALL, the observed subclass switching of anti-9-OAcSGs to IgG2, alteration in their glycosylation profile along with impairment of a few Fc-glycosylation-sensitive effector functions hints toward a disbalanced homeostasis, thereby evading the host defense. These findings justify further evaluation of the mechanism for functional unresponsiveness of antibodies and production of 9-OAcSA-specific chimeric antibodies with normal Fc domain for therapeutic applications.
authors.affiliation: Immunobiology Division, Indian Institute of Chemical Biology, 4 Raja S.C. Mullick Road, Jadavpur, Kolkata 700 032, India.
authors.forename: Suman
authors.initials: S
authors.lastname: Bandyopadhyay
authors.forename: Arindam
authors.initials: A
authors.lastname: Bhattacharyya
authors.forename: Asish
authors.initials: A
authors.lastname: Mallick
authors.forename: Asish Kumar
authors.initials: AK
authors.lastname: Sen
authors.forename: Gayatri
authors.initials: G
authors.lastname: Tripathi
authors.forename: Tanya
authors.initials: T
authors.lastname: Das
authors.forename: Gaurisankar
authors.initials: G
authors.lastname: Sa
authors.forename: Dilip Kumar
authors.initials: DK
authors.lastname: Bhattacharya
authors.forename: Chitra
authors.initials: C
authors.lastname: Mandal
mesh_terms: D002648:Child; D003602:Cytotoxicity, Immunologic / Q000276:immunology; D006001:Glycoconjugates / Q000737:chemistry / Q000276:immunology*; D006031:Glycosylation; D006801:Humans; D007074:Immunoglobulin G / Q000097:blood* / Q000276:immunology* / Q000302:isolation & purification; D054198:Precursor Cell Lymphoblastic Leukemia-Lymphoma / Q000276:immunology*; D011961:Receptors, Fc / Q000276:immunology; D012794:Sialic Acids / Q000737:chemistry / Q000276:immunology*
chemical_list: D006001:Glycoconjugates; D007074:Immunoglobulin G; D011961:Receptors, Fc; D012794:Sialic Acids