Reduced expression of programmed cell death protein 1 on peripheral regulatory B cells in pre-eclampsia – Signs of impaired immune suppression

Immunological changes are believed to be a part of pre-eclampsia etiology. This study investigated the distribution of the specific peripheral B lymphocyte phenotypes in pre-eclampsia cases compared to uncomplicated pregnancies. The study cohort included 29 women with pre-eclampsia and 14 women with uncomplicated pregnancies. Blood samples were collected in the third trimester of primigravidae pregnancies, and immune cells were analyzed using flow cytometry. Cases with pre-eclampsia showed a significantly reduced expression of programmed cell death protein 1 (PD-1) on CD27⁺CD24^hiCD38^hi regulatory B cells compared with control pregnancies (p = 0.002; multivariate logistic regression: p = 0.009). Trends for a reduced PD-1 expression on regulatory CD27⁺CD24^hi B cells and on live CD19⁺ B cells were observed in cases of pre-eclampsia (p = 0.011 and p = 0.035; respectively). No significant differences between pre-eclampsia cases and controls in percentages of B cells, B1a cells, plasmablasts, naïve B cells, transitional/immature B cells, memory B cells, regulatory CD27⁺CD24^hi B cells and regulatory CD27⁺CD24^hiCD38^hi B cells were observed. This is the first study to report reduced PD-1 expression on live B cells and regulatory B cells in pre-eclampsia. These results are in line with previous studies of peripheral regulatory T cells and decidual lymphocytes from pre-eclampsia patients. Reduced PD-1 expression on regulatory B cells in pre-eclampsia could indicate that a lack of immune suppression might play a role in the pathophysiology of pre-eclampsia.