Immunophenotyping and activation status of maternal peripheral blood leukocytes during pregnancy and labour, both term and preterm

The onset of labour in rodents and in humans is associated with physiological inflammation which is manifested by infiltration of activated maternal peripheral leukocytes (mPLs) into uterine tissues. Here, we used flow cytometry to immunophenotype mPLs throughout gestation and labour, both term and preterm. Peripheral blood was collected from non‐pregnant women and pregnant women in the 1st, 2nd and 3rd trimesters. Samples were also collected from women in active labour at term (TL) or preterm (PTL) and compared with women term not‐in‐labour (TNIL) and preterm not‐in‐labour (PTNIL). Different leukocyte populations were identified by surface markers such as CD45, CD14, CD15, CD3, CD4, CD8, CD19 and CD56. Their activation status was measured by the expression levels of CD11b, CD44, CD55, CD181 and CD192 proteins. Of all circulating CD45+ leukocytes, we detected significant increases in CD15+ granulocytes (i) in pregnant women versus non‐pregnant; (ii) in TL women versus TNIL and versus pregnant women in the 1st/2nd/3rd trimester; (iii) in PTL women versus PTNIL. TL was characterized by (iv) increased expressions of CD11b, CD55 and CD192 on granulocytes; (v) increased mean fluorescent intensity (MFI) of CD55 and CD192 on monocytes; (vi) increased CD44 MFI on CD3+ lymphocytes as compared to late gestation. In summary, we have identified sub‐populations of mPLs that are specifically activated in association with gestation (granulocytes) or with the onset of labour (granulocytes, monocytes and lymphocytes). Additionally, beta regression analysis created a set of reference values to rank this association between immune markers of pregnancy and to identify activation status with potential prognostic and diagnostic capability.