INTRODUCTION: Preeclampsia (PE) is a multisystem pathological condition occurring after 20 weeks of pregnancy. According to some scientists, the pathogenetic mechanisms of PE are based on the abnormal response of the mothers immune system to factors of placental origin.
 AIM: To assess the parameters characterizing the condition of B-cells in female patients with PE and to develop the prognostic criterion for the effective treatment of moderate PE.
 MATERIALS AND METHODS: A total of 121 women at 2436 weeks of gestation were examined. The main group included 69 pregnant women with PE in which 36 had moderate PE (group 1a, 18 women with positive effects of PE treatment; group 1b, 18 women with no effect of PE treatment) and 33 had severe PE. The control group included 52 patients with no hypertensive disorders. In the peripheral blood, the relative content of CD19+ and CD20+ В-lymphocytes and their subpopulations, namely, regulatory B-cells (CD20+IL-10+), memory B-cells (CD19+CD27+IgD), and plasmocytes (СD19+СD20-СD38+), were evaluated by flow cytofluorometry. Statistical analysis was performed using Statistica for Windows 6.0, Microsoft Excel 2010, and MedCalс programs. The diagnostic significance of the studied parameters was evaluated by ROC analysis.
 RESULTS: The comparison of all the studied parameters of the content of B-lymphocytes and its subpopulations did not reveal any significant differences in patients with PE of different severities (p 0.05 in all cases). In the comparative analysis of women with moderate PE exhibiting either positive or no treatment effects, a low level of CD20+В-lymphocytes and a high level of CD19+CD20-CD38+ plasmocytes were noted in the former. In addition, the presence of 2.8% of CD19+CD20-CD38+ cells in the peripheral blood predicts a positive treatment effect on moderate PE, while 2.8% predicts an ineffective treatment and aggravation of the PE.
 CONCLUSION: The reduction of plasmocytes and absence of treatment effect on moderate PE may be associated with the migration of plasmocytes to the target organs, which leads to the worsening of the immunopathological process during the course of PE. The content of CD19+CD20-CD38+ cells in the peripheral blood can be used to predict treatment efficacy on moderate PE.