International Immunology Advance Access originally published online on January 3, 2005
International Immunology 2005 17(2):177-191; doi:10.1093/intimm/dxh198
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
© 2005 The Japanese Society for Immunology
Over-expressed IgG2 antibodies against O-acetylated sialoglycoconjugates incapable of proper effector functioning in childhood acute lymphoblastic leukemia
1 Immunobiology Division, Indian Institute of Chemical Biology, 4 Raja S.C. Mullick Road, Jadavpur, Kolkata 700 032, India
2 Bose Institute, P-1/12 CIT Scheme VII M, Kolkata 700 054, India
3 Department of Organic Chemistry and 4 Cell Physiology Division, Indian Institute of Chemical Biology, 4 Raja S.C. Mullick Road, Jadavpur, Kolkata 700 032, India
5 Department of Pathology, Vivekananda Institute of Medical Sciences, 99 Sarat Bose Road, Kolkata 700 019, India
Correspondence to: C. Mandal; E-mail: cmandal{at}iicb.res.in
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 
2–6 manner (9-OAcSA2–6GalNAc) 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 (IgGALL) and normal individuals (IgGN) 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 Fc
R, 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 FcR. 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.
Keywords: anti-9-OAcSGs, effector function, glycosylation, subclass