The strength of IgG1 interaction can also be affected by FcγR polymorphism and in the context of therapeutic mAbs, variation in FcγRIIIa is particularly important. The most common and possibly clinically significant polymorphism is phenylalanine/valine variation at position 158 in the IgG‐binding site, wherein FcγRIIIa‐F158 binds IgG1 less well than the FcγRIIIa‐V158 form.