Study on the immunosuppressive activities of myeloid derived suppressor cells in patients suffering from recurrent spontaneous abortion
Objective 
To investigate the roles of myeloid derived suppressor cells (MDSCs) in the maintenance of maternal immune tolerance and to analyze their associations with recurrent spontaneous abortion (RSA). 
 
 
Methods 
Peripheral blood samples were collected from sixty subjects including non-pregnant healthy subjects, normal pregnant women and women with recurrent spontaneous abortion aged 25 to 35 years (n=20). Flow cytometry analysis was performed to monitor the changes of MDSCs at the 12th, 24th and 36th weeks of gestational age in three normal pregnant women. The differences with the numbers of MDSCs during the same stage of pregnancy in peripheral blood samples were compared among the three groups by flow cytometry analysis. RT-PCR analysis was used for detection of Arg-1 in women with normal pregnancy and RSA. CD8+ T cells were separated from non-pregnant healthy subjects by using magnetic beads. The immunosuppressive effects of MDSCs, isolated from women with normal pregnancy and RSA, on CD8+ T cells were evaluated by using the 3H thymidine incorporation assay. 
 
 
Results 
The number of MDSCs increased during normal pregnancy and the differences among different weeks were significant (12th week vs 24th week: P=0.0442, 24th week vs 36th week: P=0.0233, 12th week vs 36th week: P=0.0017). The percentages of MDSCs in peripheral blood of the healthy non-pregnant women were the lowest [(0.937±0.127)%], followed by those in women with RSA [(2.151±0.185)%] and normal pregnant women [(3.777±0.427)%]. There was significant difference with the percentage of MDSCs between women with normal pregnancy and RSA (P=0.0250). Compared with women with normal pregnancy, those with RSA showed significantly decreased levels of Arg-1 (P=0.0474) and suppressed activities of MDSCs against CD8+ T cell proliferation (P=0.0230). 
 
 
Conclusion 
The MDSCs might play an important role in the maintenance of maternal immune tolerance. Decreased number and inhibited function of MDSCs in the peripheral blood of women with RSA might be responsible for the development of RSA. 
 
 
Key words: 
Myeloid derived suppressor cell; Maternal immune tolerance; Recurrent spontaneous abortion