Avidity confers FcγR binding and immune effector function to aglycosylated immunoglobulin G1

Immunoglobulin G (IgG) antibodies are an integral part of the adaptive immune response that provide a direct link between humoral and cellular components of the immune system. Insights into relationships between the structure and function of human IgGs have prompted molecular engineering efforts to enhance or eliminate specific properties, such as Fc-mediated immune effector functions. Human IgGs have an N-glycosylation site at Asn297, located in the second heavy chain constant region (CH2). The composition of the Fc glycan can have substantial impacts on Fc gamma receptor(Fc gamma R) binding. The removal of the glycan through enzymatic deglycosylation or mutagenesis of the N-linked glycosylation site has been reported to silence Fc gamma R-binding and effector functions, particularly with assays that measure monomeric binding. However, interactions between IgGs and Fc gamma Rs are not limited to monomeric interactions but can be influenced by avidity, which takes into account the sum of multimeric interactions between antigen-engaged IgGs and Fc gamma Rs. We show here that under in vitro conditions, which allowed avidity binding, aglycosylated IgGs can bind to one of the Fc gamma Rs, Fc gamma RI, and mediate effector functions. These studies highlight how the valency of a molecular interaction (monomeric binding versus avidity binding) can influence antibody/Fc gamma R interactions such that avidity effects can translate very low intrinsic affinities into significant functional outcomes. Copyright (c) 2012 John Wiley & Sons, Ltd.