Increased IL-10-competent regulatory B cells in the decidua of early human pregnancy

Regulatory B cells (Bregs) may play a pivotal role in maintaining human pregnancy. For the first time, to the best of our knowledge, this study noted that cell percentages of CD24hiCD38hi Bregs and CD24hiCD27+ Bregs, which can potentially produce IL-10, are increased in human decidua compared with the mid-luteal phase endometrium. In each case of decidua, the correlation between Bregs and dendritic cell (DC) or natural killer (NK) cell expression was further explored. A positive correlation between the percentage of CD24hiCD38hi Bregs and CD123−CD11c+ myeloid DCs (mDCs) was noted. Furthermore, a significant positive correlation was also observed between the percentage of CD24hiCD27+ Bregs and CD94+CD56brightCD16− suppressive NK cells. These findings regarding decidual Bregs deepen the understanding of the harmonious immunological microenvironment that sustains early human pregnancy. •Decidual regulatory B cells (Bregs) in early human pregnancy were explored for the first time.•CD24hiCD38hi and CD24hiCD27+ Bregs significantly increased in human decidua than in non-pregnant endometrium.•IL-10 production by Bregs with ex vivo stimulation was confirmed.•A positive correlation between CD24hiCD38hi Bregs and mDCs and between CD24hiCD27+ Bregs and suppressive NK cells in decidua was found.