Mouse FcγRI:: identification and functional characterization of five new alleles

The mouse Fcgr1 gene encoding the high-affinity IgG receptor (Fc gamma RI) exists as two known alleles, Fc gamma RI-BALB and Fc gamma RI-NODI and these alleles exhibit functional differences. To determine whether other alleles exist in mouse strains, Fcgr1 coding regions from 35 strains of mice were sequenced and a further five alleles were identified, The Fc gamma RI-BALB and NOD alleles are now designated the "a" and "d'' alleles, respectively. Analysis of the five new alleles revealed that although no polymorphisms were observed in the two leader exons, nucleotide and subsequent amino acid changes were observed in the exons encoding the extracellular domains, and transmembrane and cytoplasmic tail. The cDNA of the seven alleles (a-g) were isolated and transiently transfected into COS cells, and IgG-binding studies were performed. Receptors encoded by four of the five new alleles (b, c, f, g) bound IgG2a with high affinity, displaying IgG binding characteristics similar to the a allele (previously Fc gamma RI-BALB). The d allele (previously Fc gamma RI-NOD) and the e allele [derived from Mus spretus (SPRET/Ei)] encoded receptors which showed broader specificity by binding monomeric IgG2a, IgG2b, and IgG3.