T Regulatory Cell Activation Exists in Pathogenesis of Polycythaemia Vera.
Authors: Wang Xin , Zhao Wenbo , Liu Yanxia , Li Ying 
Published: October 2019

Polycythaemia vera (PV) is a clonal disorder arising from a pluripotent hematopoietic progenitor cell. The etiology of PV remains unknown and there is no consensus as to the optimal therapy for this disorder. T regulatory (Treg) cells play a vital role in the maintenance of self-tolerance, control of auto-immunity and regulation of T-cell homeostasis, and they modulate overall immune responses against a variety of pathogens. Recent studies revealed that Treg cells play a crucial role in the process of hematopoietic activity. However, the effect of Treg cells in PV has not been reported. The Treg cells might participate in the dysfunction of T-cell immunity in PV. The profile and function of Treg cells in PV patients were explored in this study. Peripheral blood was withdrawn from 21 PV patients (Female 8 ; Male 13), as well as 25 age-matched healthy donors (F 9 ; M 16) as controls. All samples were taken after informed consent and collected from PV patients prior to treatment. Diagnoses of PV were made according to clinical and laboratory criteria. The peripheral blood mononuclear cells (PBMCs) were subjected to flow cytometry analyses after labeling with anti-CD4, anti-CD25, and anti-Foxp3 antibodies. Real-time PCR and Western blotting were also performed to identify quantitative FOXP3 mRNA expression and protein level in the PBMCs from PV in comparison to controls. The relationships between the percentage of Treg cells, the expressions for quantitative mRNA and protein, with the clinical data were assessed. The percentage of CD4+ T-cells was significant decreased in the group of PV than in normal control (28.7±7.07% vs 38.6±8.38%, p<0.05). But the percentage of CD4+CD25+FOXP3+ T-cells (Treg cells) in PV patients was significantly increased when compared to the control (10.93±4.02% vs 5.86±1.99%, p<0.05). Moreover, the quantitative mRNA expression of FOXP3 (64.23±18.52 vs 16.06±4.78, p<0.05) and protein expression of FOXP3 (0.74±0.16 vs 0.62±0.10, p<0.05)) were significantly enhanced in PV patients (shown in Figure 1). In conclusion, we showed that patients with PV have enhanced percentage of Treg cells in their peripheral blood. This was substantiated further with the finding that overexpressions of FOXP3 in PV both in mRNA and protein level. These results highlight important Treg-cell abnormalities in patients with PV because natural Treg cells are significantly increased in number and function. The underlying mechanism is still undefined, but the increased frequency and function of Treg cells might account for the abnormal T cell immunity in PV patients. It was suggested that there may be differently suppressive machanisms for Treg in these patients. The elevated Treg cells in PV might be activated and then affect the hematopoietic activity. We believe that Treg cells might involved in the dysfunction of T/NK cells in their disability to downregulate the hematopoietic proliferation in PV. And the expansion of Treg cells may be a feature of PV and associated with the pathogenesis of PV. Further investigation in this abnormality might provide novel therapy clue for this disease.

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