[Target cells of cytotoxic T cells in severe aplastic anemia in vitro]

To clarify the specific target of severe aplastic anemia (SAA) immune attack via identifying the target cells of cytotoxic T cell attacks and the expression of apoptosis ligand on each department and each stage of bone marrow hematopoietic cells.

A total of 15 SAA patients and 15 normal controls were recruited in the Department of Hematology, Tianjin Medical University General Hospital between March 2011 and March 2012. Factor associated suicide(Fas) protein expression of CD34(+) , CD14(+) , CD33(+) , and GlycoA(+) cells in bone marrow was detected by flow cytometry. The CD8(+) T cells of SAA patients and CD3(-) bone marrow mononuclear cells (BMMNC) of controls were sorted by immunomagnetic separation and co-cultured for 72 hours. The apoptosis rate of CD34(+) , CD14(+) , CD33(+) , and GlycoA(+) cells were measured with flow cytometry.

The expression of Fas protein in CD34(+) cells in SAA patients (46.59%± 27.60%) was significantly higher than that in control group (8.89%±7.28%, P<0.01). The expressions of Fas protein in CD14(+) , CD33(+) and GlycoA(+) cells in SAA group(29.29%±9.23%, 46.88%±14.30%, 15.15%±9.26%) were lower than those in control group(51.25%±38.36%, 72.06%±39.88%, 50.38%±39.88%, all P<0.05). The apoptosis rates of CD34(+) , CD33(+) and CD14(+) cells in the experimental group (CD8(+) T cells of SAA patients co-cultured with CD3(-) BMMNC of controls: 55.43%±20.50%, 38.13%±20.10%, 61.87%±21.65%)were significantly higher than those of the control group (CD8(+) T cells of controls co-cultured with CD3(-) BMMNC of controls: 35.02%±13.95%, 23.44%±10.33%, 37.04%±22.41%, all P<0.05).

Cytotoxic T cells in SAA patients may have a killing effect on hematopoietic stem/progenitor cells, and granulocytic and macrophagocytic cells from normal bone marrow. Moreover, Fas/Fas ligand-mediated apoptosis may play an important role in the immune pathogenesis of SAA. CD34(+) cells show markedly increased Fas protein expression, which may be the main target cells in the process of immune injury in SAA patients.