Interplay between Affinity and Valency in Effector Cell Degranulation: A Model System with Polcalcin Allergens and Human Patient–Derived IgE Antibodies

Abstract

An allergic reaction is rapidly generated when allergens bind and cross-link IgE bound to its receptor Fc«RI on effector cells, resulting in cell degranulation and release of proinflammatory mediators. The extent of effector cell activation is linked to allergen affinity, oligomeric state, valency, and spacing of IgE-binding epitopes on the allergen. Whereas most of these observations come from studies using synthetic allergens, in this study we have used Timothy grass pollen allergen Phl p 7 and birch pollen allergen Bet v 4 to study these effects. Despite the high homology of these polcalcin family allergens, Phl p 7 and Bet v 4 display different binding characteristics toward two human patient-derived polcalcin-specific IgE Abs. We have used native polcalcin dimers and engineered multimeric allergens to test the effects of affinity and oligomeric state on IgE binding and effector cell activation. Our results indicate that polcalcin multimers are required to stimulate high levels of effector cell degranulation when using the humanized RBL-SX38 cell model and that multivalency can overcome the need for high-affinity interactions.

Multivalent Probes in Molecular Imaging: Reality or Future?

“…Because MMIAs are more likely to be toxic than small monovalent molecules, they should be tested for cytotoxicity as well as for binding affinity and specific binding. In addition, nonspecific protein binding should be determined by structure-activity relationships or surface plasmon resonance following incubation with blood plasma proteins [53,[69][70][71].…”

Filling the Antibody Pipeline in Allergy: PIPE Cloning of IgE, IgG1 and IgG4 against the Major Birch Pollen Allergen Bet v 1

“…This finding appears to go against the textbook knowledge that a single-epitope allergen can only be crosslinked by polyclonal IgE. However, the formation of allergen multimers would not only theoretically allow crosslinking of monoclonal antibodies [ 8 ], but was recently shown in detail in a study with Timothy grass pollen allergen [ 48 ]. Recent degranulation studies with an engineered Bet v 1 trimer confirm this notion [ 44 ].…”

The Effector Function of Allergens

“…The complex relationship between the IgE repertoire and IgE affinity has been recently explored (38,72,73) underscoring the importance of tIgE, sIgE, IgE binding affinity and the diversity of the epitopes that bind IgE (72)(73)(74). The extent of effector cell activation is also linked to an allergen's oligomeric state, and the valency, spacing/proximity and flexibility of the IgE-binding epitopes (75,76).…”