Heterogeneous IgE glycoforms characterized by differential recognition of an endogenous lectin (IgE-binding protein)

IgE is highly glycosylated, but the function of the oligosaccharide side chains is largely unknown. The previous discovery of an animal lectin, IgE-binding protein (εBP), affords an opportunity to study potential carbohydrate-dependent effector functions of IgE. εBP is a β-galactoside-specific lectin with binding affinity for IgE and is now known to be equivalent to carbohydrate-binding protein 35 and the Mac-2 Ag; thus, it may have multiple functions in addition to IgE binding. We have previously shown that rat rβBP recognizes sialidase-treated human myeloma IgE to a much greater extent than the untreated IgE. In contrast, human eBP binds essentially equivalently to a monoclonal murine IgE with or without sialidase pretreatment. To validate a possible role for βBP in the IgE system, we investigated the pattern of recognition of εBP for various polyclonal human IgE samples. We show that polyclonal IgE derived from four individuals with hyperIgE syndrome or atopic dermatitis recognizes εBP and that there is individual variation in the proportion of IgE recognized by εBP, ranging from >60% for one sample to almost undetectable levels in another. We conclude that εBP does indeed recognize polyclonal IgE and that this recognition is modulated by sialylation of IgE oligosaccharides. Furthermore, there exist different IgE glycoforms, varying in the degree of sialylation, and these are distributed in a distinct manner in different individuals.