Neutrophil Phagocytic and Migratory Phenotypes in Response to Factors Within the Gestational Environment — 112a — Samantha Knudson, Faith Burns

Neutrophils make up 70% of all white blood cells. They instigate the process of labor by migrating through fetal membranes and into the lower uterus, causing a sterile inflammatory reaction. Neutrophils also migrate through the uterus during intrauterine infections to phagocytose bacteria, which can cause preterm labor. However, the specific mechanism of this migration and inflammation is unknown. Understanding how the gestational environment influences neutrophil phagocytic activation and migration may help identify a trigger for the physiological shift into labor.

Placentas from Cesarean sections were dissected to obtain pooled chorion extract (CE) and amnion extract (AE). Neutrophils were isolated from non-pregnant females and preincubated with either AE or CE with and without third-trimester hormones. The neutrophils were then incubated with either pHrodo E.coli BioParticle conjugates or dyed Escherichia coli K1 and Group B Streptococcus aureus (bacteria involved in some common gestational infections) to visualize phagocytosing neutrophils. After preincubation, pHrodo was added, and the neutrophils’ phagocytic ability was examined in the presence of cortisol, a critical stress hormone. Phagocytosis was inhibited by the combination of fetal membrane tissues and third trimester hormones. When these neutrophils were exposed to cortisol, phagocytosis was also inhibited, further suggesting immunoregulatory mechanisms within the gestational environment.

A migration assay analyzed how neutrophils’ chemoattraction varied between fetal membranes and in the presence of third-trimester hormones. After being treated with hormones, the neutrophils were added to wells containing semipermeable membranes, allowing migration towards C-section AE or CE. Neutrophils migrated more towards CE than AE, indicating greater chemoattractibility of the chorion. There is evidence that fetal membrane extracts and third trimester hormones are both necessary for down-regulating neutrophil inflammation. As Cesarean sections have not reached the physiological transition into parturition, further research using spontaneous term labor placentas is required to understand neutrophil behaviors and phenotypes leading to labor.

Augustana University
Dr. Jennifer Gubbels