Fas antigen (CD95) and hematopoietic progenitor cells

Area of Science:

• Hematology
• Immunology
• Cell Biology

Background:

• Hematopoietic progenitor cells (HPCs) are crucial for blood cell formation.
• The Fas receptor (CD95) is a key mediator of apoptosis.
• Understanding Fas expression on HPCs is vital for comprehending hematopoietic regulation.

Purpose of the Study:

• To investigate the expression and function of Fas on human CD34+ hematopoietic progenitor cells.
• To determine the inducers of Fas expression on HPCs, including cytokines and ionizing radiation.
• To explore the role of Fas in apoptosis of HPCs during in vitro expansion.

Main Methods:

• Flow cytometry was used to detect Fas and Bel-2 expression on CD34+ cells.
• Cells were cultured in serum-free conditions with interferon-gamma (IFN-gamma) and/or tumor necrosis factor-alpha (TNF-alpha).
• Apoptosis was induced using anti-Fas monoclonal antibody (MoAb) and assessed.
• The effect of ionizing radiation on Fas expression was evaluated.

Main Results:

• Freshly isolated CD34+ cells did not express Fas, but IFN-gamma and TNF-alpha induced dose-dependent Fas expression.
• TNF-alpha-induced Fas expression involved the p55-TNF-alpha receptor.
• Induced Fas was functional, mediating apoptosis upon anti-Fas MoAb stimulation.
• Low-dose ionizing radiation also induced dose-dependent Fas expression on CD34+ cells.
• In vitro expanded CD34+ cells gradually expressed Fas and lost Bel-2 expression, becoming susceptible to Fas-mediated apoptosis.

Conclusions:

• Functional Fas can be induced on hematopoietic progenitor cells by negative regulators (cytokines), ionizing radiation, and positive regulators (growth factors).
• The Fas system plays a significant role in regulating hematopoietic progenitor cells in both physiological and pathological states.
• Fas-mediated apoptosis is a relevant mechanism in HPCs, particularly during in vitro expansion and under stress conditions.