3.4 IgG1 and IgG4 bind to human FcγRIIβ with similar affinity
In comparison to other Fcγ receptors, the affinity of IgG antibodies to
the FcγRIIβ is low even if immune-complexed to antigens. We nevertheless
measured the affinity of IgG1 and IgG4 antibodies to FcγRIIb (CD32b) by
Biolayer Interferometry using Octet technology 42. To
this end, biotinylated recombinant human FcγRIIβ was immobilized on
streptavidin biosensor before incubation with either F127, G078 and A044
in either IgG1 or IgG4 format. As shown in Figure 4, IgG1 and IgG4
antibodies bound with similar affinity to recombinant FcγRIIβ (Figure 4A
and Table 1).
We also investigated the effects of immune complex formation on the
binding of IgG1 or IgG4 to FcγRIIb by BLI, performing the association
step with IgG1 and IgG4 F127 either in monomeric or in complex form with
dimeric Fel d 1 (Figure 4 C). The results showed similar association
rate (kon) for monomeric and complexed IgG1 and IgG4
whereas the dissociation rate (koff) was 10 times less
for the uncomplexed forms of IgG1 and IgG4 indicating an overall higher
binding for IgG immune complexes than for IgGs alone. Hence, antibody
subclass may have a limited influence on FcγRIIβ binding in both
monomeric and complexed form thereby confirming the results obtained in
the above cellular assays.