Functional expression of Fas antigen (CD95) on hematopoietic progenitor cells

Area of Science:

• Immunology
• Hematology
• Cell Biology

Background:

• Hematopoietic progenitor cells (HPCs) are crucial for blood cell formation.
• Interferon-gamma (IFN-gamma) and tumor necrosis factor-alpha (TNF-alpha) are known negative regulators of hematopoiesis.
• The precise mechanisms by which these cytokines suppress hematopoiesis are not fully understood.

Purpose of the Study:

• To investigate the expression of the apoptosis-associated antigen Fas (CD95) on HPCs.
• To determine the effect of IFN-gamma and TNF-alpha on Fas expression in HPCs.
• To elucidate the functional consequences of Fas induction on HPCs.

Main Methods:

• Isolated CD34+ bone marrow cells.
• Cultured cells in serum-free medium with or without IFN-gamma and/or TNF-alpha.
• Assessed Fas and Fas mRNA expression using flow cytometry and RT-PCR.
• Induced apoptosis using anti-Fas antibody and evaluated cell viability, morphology, DNA fragmentation, and colony-forming capacity (CFC).

Main Results:

• Freshly isolated CD34+ cells did not express Fas.
• IFN-gamma and/or TNF-alpha dose-dependently induced Fas and Fas mRNA expression on CD34+ cells after 48 hours.
• Synergistic effect observed when both cytokines were used together.
• TNF-alpha-induced Fas expression was mediated by the p55 TNF-alpha receptor.
• Induced Fas expression rendered CD34+ cells susceptible to apoptosis upon anti-Fas antibody treatment, evidenced by decreased viability, DNA fragmentation, and reduced CFCs (CFU-GM, BFU-E).

Conclusions:

• IFN-gamma and TNF-alpha induce functional Fas on hematopoietic progenitor cells.
• Fas induction by these cytokines contributes to the suppression of hematopoiesis.
• This pathway represents a potential mechanism for negative hematopoietic regulation.