**4.3 Polymorphisms of receptors**

Another factor influencing the affinity of antibody molecules is the existence of several polymorphisms for the unique FcγRIIa and FcγRIIIb present on human neutrophils [64]. There are two isoforms for FcγRIIa with different amino acids at position 131. These are identified as low-responder (H131) and high-responder (R131) [65]. Similarly, for FcγRIIIb two isoforms exist differing at four positions, NA1 (R36 N65 D82 V106) and NA2 (S36 S65 N82 I106) [66], and with different glycosylation patterns [67]. In addition, another FcγRIIIb isoform named SH is generated by a point mutation (A78D) in the NA2 allele [68]. These multiple FcγR isoforms display diverse binding affinity for different IgG classes [35], creating variable cell responses to different antibodies.
