An unexpected protective role of low-affinity allergen-specific IgG through the inhibitory receptor Fc?RIIb - 06/08/18

Doi : 10.1016/j.jaci.2017.09.054

Lisha Zha, PhD ^a, Fabiana M.S. Leoratti, PhD ^a, Lichun He, PhD ^c, Mona O. Mohsen, MSc ^b, Mark Cragg, PhD ^d, Federico Storni, MD ^a, Monique Vogel, PhD ^a,^⁎ , Martin F. Bachmann, PhD ^a,^b,^⁎
^a Immunology, RIA, Inselspital, University Hospital Bern, Bern, Switzerland
^b Jenner Institute, University of Oxford, Oxford, United Kingdom
^c Biozentrum, University of Basel, Basel, Switzerland
^d Antibody and Vaccine Group, Cancer Sciences Unit, Faculty of Medicine, General Hospital, University of Southampton, Southampton, United Kingdom

^∗Corresponding author: Martin F. Bachmann, PhD, Immunology, RIA, University of Bern, Inselspital, 3010 Bern, Switzerland; the Jenner Institute, University of Oxford, UK.Immunology, RIAUniversity of BernInselspital3010 Bern, Switzerland; the Jenner Institute, University of OxfordUK^∗∗Monique Vogel, PhD, Immunology, RIA, University of Bern, Inselspital, Bern 3010, Switzerland.Immunology, RIAUniversity of BernInselspitalBern3010Switzerland

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Abstract

Background

Induction of allergen-specific IgG antibodies is a critical parameter for successful allergen-specific immunotherapy. IgG antibodies can inhibit IgE-mediated mast cell activation through direct allergen neutralization or through the inhibitory receptor FcγRIIb. The affinity of IgE antibodies to the allergen has been shown to be critical for cellular activation.

Objective

Here we addressed the question of affinity thresholds of allergen-specific IgG antibodies for inhibition of mast cell activation using 2 different mAbs against the major cat allergen Fel d 1 both in vitro and in vivo in mice.

Methods

Sequences of the 2 high-affinity mAbs were back-mutated to germline, resulting in low-affinity (10⁻⁷ mol/L) antibodies of the exact same specificity.

Results

Using these newly generated recombinant antibodies, we demonstrate that low-affinity antibodies are still able to inhibit mast cell activation through FcγRIIb but do not neutralize the allergen.

Conclusion

Antibody affinity dictates the mechanism of mast cell inhibition, and IgG antibodies triggering the inhibitory FcγRIIb pathway can show a broader cross-reactivity pattern than previously thought. This indicates that allergen-specific immunotherapy generates a larger protective umbrella of inhibitory IgG antibodies than previously appreciated.

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Graphical abstract

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Key words : Allergy, vaccination, FcγRIIb-mediated inhibition, Fel d 1, low-affinity antibodies

Abbreviations used : BMMC, DARPin, FACS, RU, SIT

Plan

Methods

Mice

Cloning, expression, and purification of germline monoclonal anti–Fel d 1 IgG_2a

Bone marrow–derived mast cells

Flow cytometry

Affinity measurement using surface plasmon resonance

Epitope mapping

BMMC degranulation

Ear prick test

Passive systemic anaphylaxis

Results

Binding properties of Fel d 1–specific germline antibodies

Fel d 1–specific germline IgG_2a inhibits BMMC degranulation in vitro

Inhibitory effect of germline IgG_2a in vitro is FcγRIIb dependent

Fel d 1–specific germline IgG_2a antibody blocks mast cell activation in vivo

Discussion

	Supported by funding of the Swiss National Science foundation (SNF grant 31003A 149925 to M.F.B.).
	Disclosure of potential conflict of interest: M. Cragg has consultant arrangements with Bioinvent International and has received payment for lectures from Baxalta. M. F. Bachmann is a board member of Hypo Pet. The rest of the authors declare that they have no relevant conflicts of interest.