The four polymorphisms of low-affinity receptors genotyped in our study have each been demonstrated to affect functions of their encoded receptors. In FCGR2A, the G.A SNP at amino acid position 131 results in a histidine (H) to arginine (R) change (FCGR2A 131H/R), resulting in reduced affinity of the correspondent receptor to IgG2 [33, 34] . The T.G SNP at position 158 of FCGR3A causes a phenylalanine (F) to valine (V) substitution (FCGR23A 131F/V) and FCGR3A 158V/V encoded receptors show higher affinity to IgG1 and IgG3 [35, 36] . In the FCGR3B gene, five nucleotides (141,147,227,277 and 349) are combined to form two main haplotypes termed FCGR3B NA1 and FCGR3B NA2, and receptor encoded by FCG3B NA1 haplotype binds to IgG1 and IgG3 more easily [37] . Finally, FCGR2B 232I/T causes an isoleucine (I) to threonine (T) substitution in the transmembrane domain [22, 38] and receptors encoded by FCGR2B 232T are unable to interact with activating receptors [39] .