Changes of the functional phenotype of circulating monocytes during pregnancy

Abstract

Rearrangement of the immune system during pregnancy is a strictly controlled, dynamic process in which the first and third trimesters are pro-inflammatory, while the second corresponds to the anti-inflammatory phase. However, the involvement of monocytes in regulating the balance between inflammatory and anti-inflammatory statuses remains poorly understood. It is known that the functional phenotype of monocytes depends on their subset affiliation, assessed by the expression of CD14 and CD16, and is associated with the expression of M1(CCR2)- and M2(CD206)-associated molecules, which characterise monocytes with pro- and anti-inflammatory activity, respectively. In the given work, we have investigated the expression of CCR2 and CD206 in classical (CD14++CD16−, cMo), intermediate (CD14++CD16+, iMo), and non-classical monocytes (CD14+CD16++, nMo) in pregnant women with different gestational ages in comparison with fertile non-pregnant women. The study included 60 pregnant women, in particular 14 in the first trimester, 20 in the second trimester, and 26 in the third trimester of gestation, as well as 29 fertile non-pregnant women. One-way analysis of variance in the non-pregnant and pregnant women in the first, second, and third trimesters revealed significant differences in the expression of CCR2 and CD206, which were more pronounced in classical and intermediate monocytes and were stronger in relation to CD206 expression. Overall, monocytes from pregnant women were characterised by decreased CCR2 expression and increased CD206 expression, suggesting a shift in the immune balance towards an anti-inflammatory profile. These changes were already manifested in the first trimester (as an increased level of the mean fluorescence intensity [MFI] of CD206 in cMo and iMo, p<0.05) and reached maximum in the second trimester, manifested by a statistically significant increase in CD206 expression (% of cells, MFI) and decrease in CCR2 expression (% of cells, MFI) in all monocyte subsets. In the third trimester, the proportion of CD206+ cMo decreased compared to the second trimester (p<0.05), and the relative content of CCR2+ cells in cMo and iMo increased. Of note, in the first and third trimesters, the identified changes were combined with an increase in the pro-inflammatory monocyte profile, which was restricted by non-classical monocytes (increase of CCR2 MFI) in the first trimester and by intermediate and non-classical monocytes (significant increase in CCR2+ cells, including due to the expansion of CCR2+CD206+ co-expressing cells) in the third trimester. The data obtained indicate the involvement of monocytes in the regulation of the pro- and anti-inflammatory balance during pregnancy, with the predominant formation of the M2 profile in classical monocytes in the first and third trimesters and in all monocyte subsets in the 2nd trimester and an increase in the M1 proinflammatory profile in intermediate and non-classical monocytes in the first and third trimesters.

Keywords

• monocyte subsets
• pregnancy
• immune adaptation
• м1- м2-associated markers
• ccr2
• cd206