Expression of arginase 1 and tyrosine kinase Mer by blood monocytes in the dynamics of physiological pregnancy

During pregnancy, the maternal immune system must maintain tolerance to paternal antigens, at the same time being able to eliminate pathogens, which is achieved by the weakening of adoptive immunity and the activation of innate immunity, in particular, monocytes. However, the question about the functional phenotype of monocytes, having not only pro-inflammatory, but also anti-inflammatory activity, remains open. In the given work, we have investigated the expression of M2-associated suppressive markers Arg1 and MerTK in monocyte subpopulations during uncomplicated pregnancy. Fifty-three pregnant women with uncomplicated gestation were recruited, including 14 pregnant in the 1st trimester, 20 – in the 2nd and 19 – in the third pregnancy trimester. The comparison group consisted of 15 fertile unpregnant women without aggravated somatic anamnesis, with a history of at least one childbirth. The findings showed that in the unpregnant group circulating Mo express Arg1 and MerTK, and the most relative number of Arg1+ and MerTK+ cells is concentrated in intermediate and nonclassic monocytes. During pregnancy the expression of researched molecules in monocytes reliably increases. An increase in MerTK expression is manifested by a simultaneous increase in the number of MerTK+ cells and the mean fluorescence intensity of this marker; it is observed in the 1st and 2nd trimesters and registered in all three monocyte subpopulations. At the same time, an increase in Arg1 expression is manifested either by an enhancement of Arg1+ cells, or an increase in receptor density; it is registered throughout pregnancy, including the 3rd trimester, and is maximally expressed in classic monocytes. There is a direct correlation between the number of Arg1+ and MerTK+ cells in intermediate Mo, which increases with the progression of pregnancy, and in the 3rd trimester is also detected in classical and non-classical Mo. In general, the revealed increase in the expression of Arg1 and MerTK by monocytes indicates an increase in the anti-inflammatory potential of monocytes during pregnancy, and the involvement of monocytes in the regulation of the inflammatory process at the system level. Moreover, the features of Arg1 and MerTK expression in various monocyte subpopulations during pregnancy suggest that monocytes expressing Arg1 and MerTK can mediate different mechanisms of immune adaptation during pregnancy

Expression of M2-associated molecules in circulating monocyte subsets in fertile non-pregnant women and pregnant women with uncomplicated pregnancy

In humans circulating monocytes include classical (CD14++CD16- ), intermediate (CD14++CD16+) and non-classical/alternative (CD14+CD16++) monocytes, which in turn can be activated via the classical or alternative pathway. Pregnancy is accompanied by significant changes in the monocyte compartment, which is manifested by an increase in the number of circulating monocytes, including the proportion of intermediate monocytes, and a change in their function. However, the functional properties of monocyte subsets during gestation remain largely unexplored. We hypothesized that circulating monocytes may be activated in an alternative pattern and acquire features of M2 polarization (anti-inflammatory / immunosuppressive properties). The aim of the investigation was to study M2-associated markers that characterize the anti-inflammatory and immunosuppressive potential of myeloid cells in subpopulations of circulating monocytes in fertile nonpregnant women and women with uncomplicated pregnancy in the 2nd trimester. It was shown that in fertile non-pregnant women intermediate and non-classical monocytes are characterized by a higher expression of M2-associated markers (CD206, Arginase 1, MerTK) compared to classical monocytes. In the 2nd trimester of pregnancy, the expression of these molecules on monocytes increases significantly, which is manifested by 1) an increase in the proportion of CD206+ cells in subpopulations of classical and intermediate monocytes, 2) an increase in the mean fluorescence intensity of Arginase 1 in all monocyte subsets, 3) an increase in the proportion of MerTK+ cells in subpopulations of classical and intermediate monocytes and mean fluorescence intensity across all monocyte subsets. The highest content of CD206+ and MerTK+ cells in pregnant women is detected in the subpopulation of intermediate monocytes, and the highest values of the mean fluorescence intensity of Arginase 1 and MerTK – in the subpopulations of intermediate and non-classical monocytes. The data obtained demonstrate that monocytes of pregnant women in the 2nd trimester of pregnancy are characterized by signs of M2 polarization. This is confirmed not only by an increase in the expression of the M2-associated mannose receptor CD206, but also by an increase in the expression of Arginase 1 and MerTK, which mediate the immunosuppressive activity of myeloid cells and, in particular, macrophages of the M2 phenotype. Further studies of M2-associated markers in monocyte subpopulations during gestation will allow a more detailed characterization of the regulatory role of circulating myeloid cells during pregnancy