Yumi Kurokawa

An Increase in Circulating Mast Cell Colony-Forming Cells in Asthma

We compared a potential to generate mast cells among various sources of CD34+ peripheral blood (PB) cells in the presence of stem cell factor (SCF) with or without thrombopoietin (TPO), using a serum-deprived liquid culture system. From the time course of relative numbers of tryptase-positive and chymase-positive cells in the cultured cells grown by CD34+ PB cells of nonasthmatic healthy individuals treated with G-CSF, TPO appears to potentiate the SCF-dependent growth of mast cells without influencing the differentiation into mast cell lineage. CD34+ PB cells from asthmatic patients in a stable condition generated significantly more mast cells under stimulation with SCF alone or SCF+TPO at 6 wk of culture than did steady-state CD34+ PB cells of normal controls. Single-cell culture studies showed a substantial difference in the number of SCF-responsive or SCF+TPO-responsive mast cell progenitors in CD34+ PB cells between the two groups. In the presence of TPO, CD34+ PB cells from asthmatic children could respond to a suboptimal concentration of SCF to a greater extent, compared with the values obtained by those of normal controls. Six-week cultured mast cells of asthmatic subjects had maturation properties (intracellular histamine content and tryptase/chymase enzymatic activities) similar to those derived from mobilized CD34+ PB cells of nonasthmatic subjects. An increase in a potential of circulating hemopoietic progenitors to differentiate into mast cell lineage may contribute to the recruitment of mast cells toward sites of asthmatic mucosal inflammation.

STI571 inhibits growth and adhesion of human mast cells in culture

Stem cell factor (SCF)/c‐kit system is critical for human mast cell development. We thus examined the effects of STI571, an inhibitor of the c‐kit tyrosine kinase receptor, on the proliferation and function of human mast cells. STI571 at concentrations of 10−6 M or higher almost completely abolished the SCF‐dependent progeny generation from cord blood‐derived cultured mast cells through an inhibition of the tyrosine phosphorylation of c‐kit. The compound also suppressed the early phase of mast cell development. The extinction of mast cell growth induced by STI571 may be due largely to apoptosis according to the flow cytometric analysis and gel electrophoresis. Two‐hour exposure to STI571 that failed to influence the total viable cell number suppressed adhesion of the cells to fibronectin in the presence of SCF without altering the expressions of integrin molecules. Our results may provide a fundamental insight for the clinical application of STI571 in allergic disorders.

A possible role for maternal HLA antibody in a case of alloimmune neonatal neutropenia

BACKGROUND: Alloimmune neonatal neutropenia (ANN) is caused by a reaction of maternal alloantibodies with paternally inherited antigens on the fetal neutrophils. While human neutrophil antigens (HNA) antibodies are found in half of ANN cases, specific antibodies have not been defined in the remaining cases.

Apoptosis of Erythroid Precursors under Stimulation with Thrombopoietin: Contribution to Megakaryocytic Lineage Choice

Although the effect of thrombopoietin (TPO) on megakaryocyte production is well established, its role in the commitment of multipotential hematopoietic progenitors to the megakaryocytic lineage remains to be determined. In the present study, we attempted to clarify the determination process of megakaryocytic lineage as a terminal differentiation pathway under stimulation with TPO. Day 7 cultured cells grown by TPO derived from cord blood CD34+ cells were divided into four subpopulations on the basis of CD34 and CD41 expression. The CD34−/CD41− cells showed the labeling pattern of anti‐CD42b and anti‐CD9 antibodies closer to that of the CD34+/CD41− cells than the CD34+/CD41+ cells. Replating experiments revealed that approximately 40% of the CD34−/CD41− cells proliferated in response to a combination of growth factors, and more than 80% of them were pure erythroid precursors. However, this subpopulation failed to grow/survive and fell into apoptosis in the presence of TPO alone. In contrast, the CD34+/CD41+ cells, which predominantly contained megakaryocytic precursors, exerted a low but significant proliferative potential in the presence of TPO. The insufficient response to TPO of the CD34−/CD41− cells may result from the apparently low expression of c‐Mpl, as determined by flow cytometric analysis and reverse transcription‐polymerase chain reaction analysis. Therefore, these results suggest that the apoptosis of hematopoietic precursors other than megakaryocytic precursors is related to the determination of the terminal differentiation under the influence of TPO.

Specific Autoantibodies to Platelet Glycoproteins in Epstein-Barr Virus—Associated Immune Thrombocytopenia

In this study, we detected autoantibodies to platelet glycoproteins GPIIb/IIIa and GPIb/IX on platelets and in plasma in a patient with immune thrombocytopenia associated with Epstein-Barr virus—related infectious mononucleosis. In addition, we present our findings on the effectiveness of intravenous immunoglobulin therapy for immune thrombocytopenia associated with Epstein-Barr virus. Int J Hematol. 2003;78:168-170.