Relationship between Th1/Th2 balance and medical abortion outcomes in early medical abortion patients.

Incomplete abortion is a common complication of medical abortion, potentially related to immune dysregulation. The roles of dendritic cells, Th1/Th2 polarization, and formyl peptide receptor 3 (FPR3) in abortion outcomes are not well understood. We retrospectively analyzed 175 women who underwent early medical abortion between January 2022 and March 2025, classifying them into complete (CA) and incomplete abortion (ICA) groups. A murine model was also used, with mifepristone administered on embryonic days 6.5 to 8.5. FPR3 expression was significantly lower in ICA tissues compared to CA. CA samples showed higher Th1 marker levels and lower Th2 marker levels (all P < 0.001). In mice, mifepristone increased Fpr3 and Tbx21 mRNA levels by 3.5- and 4-fold, respectively, and decreased Gata3 expression by ∼55%. Protein analysis showed similar trends. Mifepristone treatment was accompanied by upregulation of FPR3 and a Th1-biased/Th2-suppressed molecular profile, suggesting a previously unrecognized immune-mediated mechanism that may complement its endocrine effects.