Systemic increase in human maternal circulating CD14+CD16- MCP-1+ monocytes as a marker of labor

Objectives: To study the influence of pregnancy and labor on the proportion and level of activation of monocyte subpopulations in human pregnancy.

Study design: Peripheral blood samples were obtained from healthy nonpregnant women (n = 6); women in the third-trimester of healthy pregnancies (n = 18) and women with preterm premature rupture of membranes (n = 46), just before delivery for the last 2 groups. Monocyte subpopulations were characterized by flow cytometry using CD14, CD16, and activation level using macrophage chemoattractant protein-1 (MCP-1) and CCR2 antibodies.

Results: The relative proportion of each monocyte subset in nonpregnant women was similar to that in women with healthy or complicated pregnancies. However, pregnancy was associated with a significant decrease in MCP-1 expressing monocytes (79.5% ± 19.8% vs 9.3% ± 6.8% and 11.9% ± 8.3% for nonpregnant, healthy pregnancy, and preterm premature rupture of membranes (respectively, P < .05). Spontaneous labor was associated with a return to nonpregnant values for the proportion of MCP-1 expressing monocytes in both normal (74.4% ± 16.9) and preterm premature rupture of membranes pregnancy (68.4% ± 35.6), irrespective of the mode of delivery (vaginal or cesarean section). This was not observed in women who delivered without spontaneous labor onset. CCR-2 (MCP-1 receptor) expression was not modified in monocytes at the time of labor, but was significantly increased in granulocytes (3646 ± 1080 vs 7338 ± 2718 for nonlaboring and laboring preterm premature rupture of membranes, respectively, P < .05) CONCLUSION: In light of previous reports of a role for MCP-1 in labor, our results suggest the downregulation of activation levels of monocytes, via MCP-1 expression might be involved in maternofetal immune tolerance. Monocyte reactivation might be associated with labor.