FcgRIIIB Gene Duplication: Evidence for Presence and Expression of Three Distinct FcgRIIIB Genes in NA(11,21)SH(1) Individuals

Recently, a new alloantigen on IgG Fc receptor type IIIb (FcgRIIIb), SH, was described (Bux et al, Blood 89:1027, 1997). We identified three healthy individuals whose neutrophils reacted positively with the SH antiserum. The neutrophil antigen (NA) phenotype of all three donors was NA(11,21). Analysis of genomic DNA showed that the three donors were positive for the described SH-encoding mutation in the NA2-FcgRIIIB gene, 266C=A. However, NA(1,2) genotyping and nucleotide sequencing of an NA2-specific fragment amplified from the genomic DNA fragment showed that these individuals carried three FcgRIIIB genes, namely, NA1FcgRIIIB, NA2-FcgRIIIB, and SH-FcgRIIIB, encoding NA1FcgRIIIb, NA2-FcgRIIIb, and SH-FcgRIIIb, respectively. Southern blot analysis confirmed these findings. Furthermore, all three transcripts were isolated from neutrophil mRNA. To investigate whether the presence of three FcgRIIIB genes resulted in a higher membrane expression of FcgRIIIb, we measured the reactivity of neutrophils from NA(11,21)SH(1) individuals with a panel of CD16 monoclonal antibodies (MoAbs) in comparison with neutrophils from NA(11,21)SH(2) controls. Reactivity of four different anti–pan-FcgRIII MoAbs and NA2specific MoAb GRM1 was higher with SH(1) neutrophils compared with controls, whereas that of NA1-specific MoAbs was similar, which is in concordance with the results from the genomic analysis. We observed that reactivity with NA2-specific CD16 MoAb PEN1 was sixfold higher in SH(1) individuals compared with controls. Apparently, the 60Ala=Asp substitution in SH-FcgRIIIb influences the epitope recognized by PEN1. In conclusion, we identified three NA(11,21)SH(1) individuals carrying three FcgRIIIB genes and observed a clear genedosage effect on the level of expression of neutrophil FcgRIIIb. r 1998 by The American Society of Hematology.