Proliferation of MDSCs may indicate a lower CD4+ T cell immune response in schistosomiasis japonica.

Background: Schistosoma japonicum (S. japonicum) is the main species of Schistosoma prevalent in China. Myeloid-derived suppressor cells (MDSCs) are important immunoregulatory cells and generally expand in parasite infection, but there is little research relating to MDSCs in Schistosoma infection.

Methods: Fifty-six S. japonicum-infected patients were included in this study. MDSCs and percentages and absolute cell numbers of lymphocyte subsets, including ^CD3+ T cells, ^CD4+ T cells, ^CD8+ T cells, B cells and natural killer (NK) cells were detected using flow cytometry. The degree of liver fibrosis was determined using color Doppler ultrasound.

Results: Patients infected with S. japonicum had a much higher percentage of MDSCs among peripheral blood mononuclear cells (PBMCs) than the healthy control. Regarding subpopulations of MDSCs, the percentage of granulocytic myeloid-derived suppressor cells (G-MDSCs) was clearly increased. Correlation analysis showed that the absolute cell counts of T-cell subsets correlated negatively with the percentages of MDSCs and G-MDSCs among PBMCs. The percentage of G-MDSCs in PBMCs was also significantly higher in patients with liver fibrosis diagnosed by color doppler ultrasound (grade > 0), and the percentage of G-MDSCs in PBMCs and liver fibrosis grading based on ultrasound showed a positive correlation.

Conclusion: S. japonicum infection contributes to an increase in MDSCs, especially G-MDSCs, whose proliferation may inhibit the number of ^CD4+ T cells in peripheral blood. Meanwhile, there is a close relationship between proliferation of G-MDSCs and liver fibrosis in S. japonicum-infected patients.