Basophil/mast cell precursors in human peripheral blood

Abstract

Semisolid (methylcellulose) hemopoietic cultures revealed the presence of histamine-containing granulocyte colonies derived from precursors (CFU-C) present in human peripheral blood. Light microscopy and histochemical studies of cells in individual histamine-containing colonies demonstrated homogeneous populations of metachromatic basophil/mast cells (BMC) at various stages of maturation. By inverted microscopy, pure BMC colonies were more often found to have the overall appearance of the previously described 'eosinophil' (type II), rather than 'neutrophil-macrophage' (type I), colony type. Histamine-positive colonies constituted 58% (50/86) of all (type I and type II) granulocyte colonies in repeated cultures from a patient with systemic mastocytosis (SM), and 19% (13/67) of colonies in cultures from 8 patients with chronic myeloid leukemia (CML); this was in contrast to 8% (12/153) of colonies in cultures from 4 patients with urticaria pigmentosa (UP) and 6 normal controls (p < 0.0001). Calculated frequency of BMC CFU-C was approximately 1 per 2 X 106 in normal and 1 per 2 X 105 nucleated cells in SM peripheral blood. Taking colony size into account, histamine content per cell in histamine-positive type II colonies in SM cultures was 1.1 ± 0.19 pg, compared to 0.29 ± 0.08 pg in CML and ≤0.10 in normals and UP. Electron microscopy (EM) of individual colonies revealed electron-dense granules with ultrastructural features of BMC in histamine-positive, but not histamine-negative, colonies. Use of these methods may help to further clarify the nature of BMC precursors and the regulation of their proliferation in bone marrow disorders and allergic states.