Sialic Acid Residues Are Essential for the Anaphylactic Activity of Murine IgG1 Antibodies

Abstract

Glycosylation of the Ab molecule is essential for maintaining the functional structure of Fc region and consequently for Ab-mediated effector functions, such as binding to cells or complement system activation. Alterations in the composition of the sugar moiety can dramatically influence Ab activity; however, it is not completely clear how differences in the N-linked oligosaccharide structure impact the biological function of Abs. We have described that murine IgG1 Abs can be separated according to their ability to elicit in vivo anaphylaxis in a fraction of anaphylactic and other of non-anaphylactic molecules. Furthermore, we showed that the N-linked oligosaccharide chain is essential for the structural conformation of the anaphylactic IgG1, the binding to FcγRIII on mast cells, and, consequently, for the ability to mediate anaphylactic reactions. In this study, we evaluated the contribution of individual sugar residues to this biological function. Differences in the glycan composition were observed when we analyzed oligosaccharide chains from anaphylactic or non-anaphylactic IgG1, mainly the presence of more sialic acid and fucose residues in anaphylactic molecules. Interestingly, the enzymatic removal of terminal sialic acid residues in anaphylactic IgG1 resulted in loss of the ability to trigger mast cell degranulation and in vivo anaphylactic reaction, similarly to the deglycosylated IgG1 Ab. In contrast, fucose removal did not affect the anaphylactic function. Therefore, we demonstrated that the ability of murine IgG1 Abs to mediate anaphylaxis is directly dependent on the amount of sialic acid residues associated to the oligosaccharide chain attached to the Fc region of these molecules.

Characterization of the allergenic potential of proteins: an assessment of the kiwifruit allergen actinidin

“…In addition to IgE antibody production, the subclass distribution of the IgG antibody response was investigated. Although IgE antibody is accepted as the major mediator of immediate hypersensitivity allergic reactions in humans, in mice a subclass of IgG (IgG1) can also sensitize mast cells and trigger anaphylaxis (Silva et al, 2008). The IgG1 subclass is subject to similar immune regulation as is IgE and is therefore used as a surrogate marker for IgE antibody responses (Birmingham et al, 2002;Robinson et al, 1996).…”

“…Systemic (intraperitoneal) administration of allergens such as latex in the absence of alum has been shown to elicit a more mixed pattern of antibody responses, with both IgG1 and IgG2a subclasses, in addition to IgE (Kurup et al, 1994). Furthermore, it is clear that only a fraction of IgG1 antibodies exhibit mast cell binding and anaphylactic properties, with this property being dependent on the glycosylation status of the molecule (Silva et al, 2008). Therefore, although the distribution of IgG1 and IgG2a antibodies is of mechanistic interest, it is probably prudent to utilize IgE antibody as the primary marker of allergenicity and to examine total IgG antibody production as a marker of immunogenicity and exposure.…”

Antigen-Fixed Leukocytes Tolerize Th2 Responses in Mouse Models of Allergy

“…Interestingly, Ag-specific IgG1 (data not shown) was also reduced in the airway inflammation model but not in the food allergy model, perhaps relating to the different routes of immunization and adjuvants employed in the two models. Since IgE and IgG1 can induce anaphylactic responses by binding Fc receptors on mast cells (25), the presence of IgG1 in the food allergy model could explain the mild anaphylactic symptoms observed in the WPE-SP tolerized group. Indeed, IgE-deficient mice still exhibit anaphylactic-like reactivity (26).…”