The expression of NA antigens in people with unusual Fcγ receptor III genotypes

BACKGROUND: The Fcγ receptor IIIb (FcγRIIIB) genes that encode neutrophil-specific antigens NA1 and NA2 differ at 5 nucleotides (nts); in 4, the result is an amino acid (AA) difference between the two alleles. The role of each of these differences in antigen expression is not known. Persons with FcγRIIIB genes that differ from NA1-FcγRIIIB and NA2- FcγRIIIB by 1 nt have been described. This study compared NA1 and NA2 expression on granulocytes in persons with variant FcγRIIIB genes and in healthy blood donors. STUDY DESIGN AND METHODS: Reactions of NA1- and NA2-specific MoAbs and alloantibodies with granulocytes were assessed by flow cytometry in 74 healthy blood donors and 6 persons with known variant FcγRIIIB genes. The granulocytes were tested with 1 NA1-specific MoAb, 1 NA2-specific MoAb, 4 NA1-specific alloantibodies, and 4 NA2-specific alloantibodies. RESULTS: Analysis of granulocytes from persons with variant NA genotypes found that single-base substitutions in FcγRIIIB at 141 and at 349 are important in NA1 expression and those at 227 and 277 are important in NA2 expression. Among blood donors, neither age, sex, nor race affected the expression of NA1 or NA2. The NA2-specific MoAb reacted more intensely with granulocytes from NA2-double-dose cells than with those from NA-single-dose cells, but this was not true for the NA2-specific alloantibodies. There was no difference in the reactions of the NA1-specific MoAbs and alloantibodies with donor samples of known NA1-double-dose or NA-single-dose cells. The intensity of reactions of both the NA1- and NA2-specific MoAbs and alloantibodies were strongly correlated on double-dose cells but not on single-dose cells. In fact, granulocytes from 7 healthy blood donors, phenotyped as NA-single-dose with the MoAbs, were phenotyped as NA2-double-dose with the alloantibodies. Variations in FcγRIIIB are common in blacks, but 5 of the 6 donors were white. These results suggest that FcγRIIIB variations may be common in both whites and blacks. CONCLUSIONS: NA2 expression is affected by polymorphisms in FcγRIIIB 227 and FcγRIIIB 277, both of which are involved in an FcγRIIIb N-glycosylation site. Polymorphisms in FcγRIIIB at 141 and 349 appear more important to NA1 expression.