3.1 IgG1 and IgG4 block activation of basophils with similar efficiency
We recently have described and characterized three monoclonal antibodies (F127, A044 and G078) against Fel d 1, the major cat allergen in humans, recognizing three non-overlapping epitopes of Fel d 1 (Figure 1A)39,40. Those variable regions were cloned in front of the human gamma 1, 4 or epsilon chain backbone to express Fel d 1 specific fully human IgG or IgE antibodies of three specificities and 2 different IgG subclasses. To test the neutralization capacity of the Fel d 1 specific IgG1 and IgG4 antibodies, basophils from 2 different individuals (A and B) suffering from cat allergy were stimulated with recombinantly expressed dimeric Fel d 1 and up-regulation of CD63 was used as a read-out for basophil activation (Figure 2). Basophils of both individuals were activated by Fel d 1 and, most importantly, all three Fel d 1 specific mAbs (G078, A044 and F127) either of the IgG1 or IgG4 subtype were able to block basophil activation with similar efficiency. This inhibition may be a mixture of allergen-neutralization and engagement of FcγRIIβ as basophils from allergic individuals likely carry polyclonal Fel d 1-specific IgE antibodies via FcεRI on their surface. To dissect these 2 possibilities, we loaded basophils from non-allergic individuals with the mAbs used above but expressed as IgE.