THE EXPRESSION OF THE NB1 ANTIGEN ON MYELOID PRECURSORS AND NEUTROPHILS FROM CHILDREN AND UMBILICAL CORDS

The neutrophil-specific antigen NB1 is expressed by neutrophils from 9 7% of healthy adults. However, membrane expression of this molecule is unique in that it is found on only a subpopulation of neutrophils pre sent in NB1-positive adults. We have investigated the ontogeny of NBI antigen expression by haematopoietic progenitor cells to determine the stage and pattern of antigen expression during granulocytic cell diff erentiation. In addition, we examined whether the ontogeny and frequen cy of granulocytic cells expressing the NB1 antigen might vary in subj ects according to age. A monoclonal antibody (MoAb) specific for NB1 ( 1B5) and flow cytometry was used to assess the frequency and character istics of the NBI-positive cells found in umbilical cord blood (n = 11 ), children (n = 37), healthy adults (n = 46) and patients with chroni c myelogenous leukaemia (n = 8). We also used flow cytometry to isolat e NB1-positive and NBI-negative bone marrow and peripheral blood cells from various tissue sources. The separated subpopulations were then a nalysed by Wright stain and light microscopy. The size of the NB1-posi tive neutrophil subpopulation in 46 healthy adults (56 +/- 19%) was id entical to that found for neutrophils from 36 children ranging in age from 8 months to 18 years (56 +/- 11%). In contrast, expression of the NBI antigen by the neutrophils present in umbilical cord blood (91 +/ - 3%, n = 11) was significantly greater than that in adults (P < 0.002 ) or children (P < 0.002). We also examined the size of the NB1-positi ve subpopulation among neutrophils from eight patients with chronic my elogenous leukaemia (CML). The NB1-positive subset in CML subjects (29 .5 +/- 22.4%) was significantly less that in healthy adults (P < 0.02) or children (P < 0.02). Marrow cells from eight adults were similarly separated and analysed. We found that 69 +/- 17% of segmented and ban d forms of neutrophils, 70 +/- 2% of metamyelocytes and 61 +/- 23% of myelocytes were NB1-positive. In fetal bone marrow, 86 +/- 9% of the s egmented and band forms, 82 +/- 10% of the metamyelocytes and 3 +/- 4% of myelocytes were NB1-positive. In conclusion, neutrophil-specific a ntigen NBI is first expressed at the myelocyte stage of myeloid differ entitation. In adult bone marrow, the percentages of myelocytes, metam yelocytes and segmented or band cells that expressed this antigen were similar and comparable in magnitude to the frequency of NB1-positive neutrophils found in the circulation. Although the size of the NB1-pos itive neutrophil subpopulation was the same in healthy adults and chil dren, it was significantly increased in umbilical cord blood, and in f etal marrow cells.