Chemoattractants in fetal membranes enhance leukocyte migration near term pregnancy

Chemoattractants in fetal membranes enhance leukocyte migration near term pregnancy | Image Credit: © Mikael Damkier - © Mikael Damkier - stock.adobe.com.

Near the end of pregnancy, chemoattractants are released by term human fetal membranes (hFM) to increase the number of leukocytes, according to a recent study published in the American Journal of Obstetrics & Gynecology.¹

Events such as implantation, uterine involution, and postpartum cervical remodeling are caused by the invasion of leukocytes into the uterus during pregnancy. Additionally, leukocyte invasion into gestational labors facilitates term and preterm labor.

A chemotactic assay was developed to improve migration of human leukocytes at delivery.² After identifying the release of chemoattractants from hFMs that lead to a response from leukocytes, experts designed the leukocyte migration assay (LMA) to have leykocytes in an upper chamber migrate to a bottom chamber through a chemoattractive extrant.¹

Investigators conducted a study to assess patterns of leukocyte migration near the end of human pregnancy when using the LMA as a bioassay. Participants were women with normal singleton pregnancy and no medical or obstetrical complications.

Women with a clinical infection, diabetes mellitus, premature rupture of membranes, nonsingleton pregnancies, immunologic problems, intrauterine growth restriction, fetal congenital diseases, receipt of progesterone or artificial oxytocin, and preeclampsia or dysfunctional labor were excluded from the analysis.

Blood draws were performed at a routine checkup during the 35th or 36th week of gestation, the start of labor, and postpartum day 3. In ex vivo studies, blood was drawn from women who were preterm not in labor, term not in labor (TNL), and term in labor (TL). TNL hFMs were obtained following cesarean delivery, vs TL hFMs following spontaneous vaginal delivery at term.

Investigators obtained 4 mL of peripheral blood from each participant, which was stored in tubes with heparin coating. After separation from erythrocytes, leukocytes were transferred to a 50-mL tube, with centrifuging performed at 120×g for 10 minutes.

Fetal membranes were obtained from TL or TNL placentas immediately after delivery and cut into 5 cm square pieces. After mincing and centrifuging, the LMA was used to assess chemoattractant activity toward leukocytes in the samples.

The LMAs used modified Boyden chemotaxis chambers (AP48; Neuro Probe, Gaithersburg, MD) divided into upper and lower compartments with a polycarbonate membrane between the 2 compartments. Thawed hFM extracts were placed into lower compartments for use as a negative control.

Flow cytometry was utilized to evaluate the types of leukocytes migrating from the upper to lower compartments. The number of beads added was multiplied by the ratio of leukocytes to beads to determine the total number of leukocytes migrated.

Leukocyte migration-responsiveness was assessed in 11 participants aged 29 to 42 years. Significant CD11b expression and a lack of other markers being expressed made 99% of migrated leukocytes be identified as neutrophils.

Analysis of variance for repeated measures testing indicated significant differences in leukocyte migration rates between the third trimester, TL, and 3 days postpartum. The peak of migration was observed during TL, but a significant decrease in levels was observed at 3 days postpartum vs the third trimester.

When evaluating migration patterns per week, investigators noted significantly higher ratios during delivery compared to 1 week and 2 weeks before delivery. The most significant increase in migration was observed from 1 week before delivery to delivery.

Cytokines and chemokines with significant increases in concentration within maternal serum included C-C motif chemokine ligand (CCL) 11, CCL20, CCL21, CCL23, interferon-Y, interleukin (IL)-4, IL-6, and IL-8. Chemoattractive activity was found in conditioned media from TNL and TL, increasing the migration of TL leukocytes.

When exposing leukocytes from TNL women to serum from either TNL or TL women, increased migration to chemoattractive extracts was observed. This indicated hFM may be the source of increased leukocyte responsiveness in maternal serum.

These results indicated significant roles of chemoattractants released by hFMs at term toward regulating leukocyte activation and migration. Investigators concluded determining the composition of hFM chemoattractants is crucial.

References

1. Lee H, Takamizu A, Nishizaki Y, et al. Activation of peripheral leukocyte migration before spontaneous labor at term. Am J Obstet Gynecol. 2024;231:539.e1-13. doi:10.1016/j.ajog.2024.02.280
2. Yuan M, Jordan F, McInnes IB, Harnett MM, Norman JE. Leukocytes are primed in peripheral blood for activation during term and preterm labour. Mol Hum Reprod. 2009;15(11):713-24. doi: 10.1093/molehr/gap054