ANALYSIS OF THE EXPRESSION OF NEUTROPHIL-SPECIFIC ANTIGEN NB1 - CHARACTERIZATION OF NEUTROPHILS THAT REACT WITH BUT ARE NOT AGGLUTINATED BYANTI-NB1

The neutrophil-specific NB antigen system has been serologically chara cterized with human alloantisera. Two alleles, NB1 and NB2, have been described. NB1 is expressed on a subpopulation of peripheral blood neu trophils in 97 percent of healthy donors. Human alloantibodies have be en used to identify the 58- to 64-kDa glycoprotein (GP) on which NB1 i s located. NB1 can usually be detected by both a granulocyte immunoflu orescence (GIF) assay and a granulocyte agglutination (GA) assay, but neutrophils from some donors have been found to react with anti-NB1 in GIF but not in GA assays. To determine if the latter neutrophils expr ess NB1 and the corresponding 58- to 64-kDa GP, these neutrophils were probed with rabbit and human sera specific for NB1. First, the propor tion of neutrophils that express NB1 was quantitated. Neutrophils from donors that typed as NB1-positive in both GA and GIF assays were anal yzed by flow cytometry with antisera to NB1. Human and rabbit anti-NB1 reacted with 71 +/- 17 percent and 70 +/- 17 percent of neutrophils, respectively. There was no difference in the expression of NB1 in NB1- homozygous and NB1-heterozygous individuals. In contrast, significantl y fewer neutrophils from four donors that typed as NB1-positive in GIF assay but not GA assay reacted with human (27 +/- 12%; p<0.001) and r abbit (26 +/- 12%; p<0.001) anti-NB1. When neutrophils from these same four donors were probed with rabbit and human anti-NB1 by immunoblott ing and immunoprecipitation, the 58- to 64-kDa GP was identified. No d ifference in the electrophoretic mobility of the 58- to 64-kDa GP coul d be detected in donors with low or high percentages of NB1-positive n eutrophils. These studies show that some neutrophils that are not aggl utinated by NB1 antibody do express NB1 and the 58- to 64-kDa GP.