BACKGROUND: Between 87 and 97 percent of whites express NB1 alloantigen on some but not all of their granulocytes. The expression of NB1 has not been compared among large groups of adults of different sexes, ages, and ethnic groups. Previous testing of whites suggests that the expression of NB1 is variable.

STUDY DESIGN AND METHODS: Serologic testing of granulocytes from 224 persons with two examples of MoAb to NB1 (1B5 and 7D8) was performed to distinguish phenotypic differences among age, sex, and ethnic groups and differences in reactivity to MoAbs. The donors were from 17 to 82 years of age, and 87 were female. They were from four ethnic backgrounds: 54 were African American (black), 10 were Asian, 9 Hispanic, and 152 white. Granulocytes were tested by flow cytometry. Parallel testing with MoAbs to CD16, CD11b, and CD45 served as controls. The size of the granulocyte population reacting with 1B5 and 7D8 and the respective mean, median, and peak cell fluorescence intensities were analyzed.

RESULTS: The expression of 7D8 and 1B5 was greater on granulocytes from female donors. The expression of 7D8 fell in older women but not in men. There were no differences among the four racial groups in either the frequency of NB1 as determined by 1B5 or 7D8 or in the size of the population of granulocytes reacting with either antibody. When the fluorescence intensities of the antibody reactions were compared among groups, there were no differences in reactivity with 1B5. However, reactions with 7D8 were all greater in blacks. Comparison of the size of the antigen‐positive granulocyte population, as determined by antibody reactivity, showed that only 30 donors differed by more than 10 percent. These discordant results were more likely to occur in whites than in blacks (18% vs. 4%, p<0.02).

CONCLUSIONS: NB1 is composed of at least two epitopes as determined by serologic studies. The expression of both antigens is greater in females. The 7D8‐reactive epitope appears to be more prevalent or more accessible on granulocytes of blacks. Variations in the expression of NB1 are more likely to occur in whites. The biochemical and molecular basis of these variations are not known.