Recently, we were able to establish the immunologic surface marker profile of human basophils and mast cells. In the present study, the characterization of these cell types was extended by the use of monoclonal antibodies (mAbs) to hemopoietic differentiation antigens. Basophils and mast cells were enriched by mAbs and complement from chronic myeloid leukemia blood (n = 5) and dispersed lung tissue (n = 4), respectively. A panel of 80 mAbs was tested for being reactive with purified cell populations using flow cytometry and/or a combined toluidine blue-immunofluorescence staining procedure. In addition to previous findings, basophils were found to react with mAbs directed against the 126-kilodalton dipeptidylpeptidase IV (CD26), platelet glycoprotein IIa (CD31), CD40 antigen known to share sequence homology with nerve growth factor receptor, leukosialin (CD43), CD44 antigen, the ICAM-1 antigen (CD54) and VIM2-reactive gangliosides involving the sialofucooligosaccharide sequence (CDw65L). Bsp-1 was found to be a specific marker for human basophils, whereas mast cells were not stained by this reagent. Basophils apparently lack CD22 antigen, gangliosides detected by CDw65 mAbs (except CDw65L) and CD71 antigen (transferrin receptor). Mast cells were found to express CD43 and CD44 antigen. In contrast, mast cells lack CD22, CD26, CD31, CD40 and CDw65 antigen. These results provide further evidence that both blood basophils and mast cells express a unique immunologic surface marker profile including binding sites for a variety of immunomodulating ligands and adhesion molecules.

Pluripotent hematopoietic progenitor cells (CFU-GEMM), myeloid progenitor cells (CFU-GM), and erythroid progenitors (BFU-E) were studied in midtrimester human fetuses using the mixed colony assay. All three progenitor cell populations were detected at high levels in the fetal liver from 12 to 23 wk of gestation. Stem cells were first observed in the bone marrow at 15–16 wk of gestation, although bone marrow cultures from earlier fetuses showed heavy growths of stromal cells. Spleen cultures first showed growth of stem cells at 18–19 wk, but fetal thymus showed no hematopoietic activity. Peripheral blood from four fetuses aged 13, 18, 20, and 21 wk showed very high levels of all 3 progenitor cells. The results demonstrate that hematopoietic development in the human fetus parallels that of the mouse. The observation that stromal cell development in the bone marrow precedes the appearance of hematopoietic progenitor cells suggests that they may be closely involved in stem cell growth.

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An IgM class monoclonal antibody Bsp-1 that selectively reacts with human basophils was used to label basophils in normal and leukaemic haemopoietic samples. The immunophenotype of Bsp-1+ basophils was determined using a panel of 21 IgG subclass monoclonal antibodies in two-colour immunofluorescence assays. Basophils expressed the leucocyte common antigen, HLA-ABC antigens and antigens defined by CD11 and CD13 monoclonal antibodies. Other myeloid cell (granulocyte-monocyte) associated anti-antigens, lymphoid cell surface determinants and HLA-DR antigens were not detected. Basophil preparations of 95-98% purity were obtained from the peripheral blood of patients with CML and umbilical cords using fluorescence activated cell sorting techniques. Purified basophils exhibited metachromatic staining with toluidine blue, alcain blue and astra blue. PAS staining was observed in 7% of cord Bsp-1+ cells and of 55% CML Bsp-1+ cells. Between 5% and 10% of basophils were chloroacetate esterase-positive which suggests that some Bsp-1+ cells are immature basophils.

he ontogeny of cells containing the enzyme terminal deoxynucleotidyl transferase (TdT) in human fetal liver, bone marrow, and thymus has been studied using a highly specific antiserum to TdT together with monoclonal antiprecursor cell antibodies in double and triple marker immunofluorescence. TdT+ cells were first observed in fetal liver at 12 wk of gestation and accounted for 55% of the lymphoid-like cells isolated after Ficoll-Hypaque separation. TdT+ cells were first observed in the bone marrow 16 wk after gestation. Like TdT+ cells in normal infant bone marrow, the majority of TdT+ cells in fetal liver and bone marrow expressed both BA-1 and RFB-1 antigens. This suggests that fetal TdT+ cells include progenitors of the B lineage (BA-1+) and perhaps of thymocytes (RFB-1+). Nevertheless, TdT was not observed in fetal thymocytes until after 20 wk of gestation, although thymic blasts and the majority of thymocytes were strongly RFB-1+ from 12 wk of gestation. These results clearly show that fetal thymus is first populated by TdT, RFB-1+, BA-1 cells, but does not exclude the fact that a second “wave” of TdT+ prothymocytes, possibly bone marrow derived, also exists.