The basophil activation marker defined by antibody 97A6 is identical to the ectonucleotide pyrophosphatase/phosphodiesterase 3

It has recently been shown that monoclonal antibody (MoAb) 97A6 detects a s urface antigen expressed on basophils and their CD34(+) precursor cells, as well as the basophil cell line KU-812. In this report the partial amino ac id sequence of affinity chromatography- and sodium dodecyl sulfate-polyacry lamide gel electrophoresis-separated 97A6 antigen(s) from KU-812 lysates wa s determined. Sequence alignment of high-performance liquid chromatography- selected tryptic peptides from the resulting 130- and 150-kd bands revealed a 100% identity with amino acids 393 to 405 of ectonucleotide pyrophosphat ase/phosphodiesterase-3 (E-NPP3;, CD203c) but not of the related ectoenzyme PC-1 (E-NPP1). Moreover, MoAb 97A6 selectively recognized 293 cells transf ected with human E-NPP3, but did not react with cells transfected with PC-1 or parental 293 cells. In addition, E-NPP3 messenger RNA expression was de tected in basophils but not other peripheral blood cells. Finally, MoAb 97A 6 immunoprecipitated phosphodiesterase activity from KU-812 cells and perip heral blood basophils, but not from other cell populations. These data demo nstrate that MoAb 97A6 recognizes the functionally active type II transmemb rane ectoenzyme E-NPP3. (Blood. 2001;97:3303-3305) (C) 2001 by The American Society of Hematology.