Monocytes are progressively activated in the circulation of pregnant women

Pregnancy is characterized by the presence of generalized leukocyte activation. We used flow cytometry to investigate changes in phenotype and intracellular cytokines of circulating granulocytes, monocytes, and T lymphocytes of pregnant women during gestation. We report that peripheral circulation of pregnancy is characterized by an increased percentage of granulocytes and a decrease in lymphocytes. The proportion of monocytes remains stable throughout gestation; however, a progressive up-regulation of surface markers CD11a, CD54, and CD64 was detected. Monocytes also showed higher production of interleukin (IL)-12 and IL-1beta compared with the nonpregnant state, and granulocytes had greater potential to synthesize IL-8. All these changes were particularly marked in late gestation. T lymphocytes did not have any characteristics of the activated state and showed a decreased IL-6 production. These findings demonstrate that activation of maternal monocytes and granulocytes increases during pregnancy and support the idea that pregnancy results in an elevation of the innate immune system and suppression of the adaptive immune system.