Differential Immune Checkpoint Expression in CD4 and CD4 NKT Cell Populations During Healthy Pregnancy.

This study investigated the expression of immune checkpoint molecules on CD4 and CD4 NKT cell subpopulations throughout healthy pregnancy trimesters and in non-pregnant condition to understand their role in maternal-fetal immunotolerance. Using flow cytometry, we found that CD4 NKT cells significantly outnumbered CD4 NKT cells in all investigated groups. In the case of the immune checkpoint molecules, PD-1 receptor expression was significantly lower in CD4 NKT cells compared to CD4 counterpart cells only in non-pregnant women, while the PD-L1 ligand expression on CD4 NKT cells significantly decreased in the third trimester. In contrast, LAG-3 and Galectin-3 expressions remained stable across all subsets and trimesters. For the TIGIT/CD226 axis, CD226 expression was significantly higher in CD4 NKT cells in the third trimester and in non-pregnant women. The two ligands CD112 and CD155 were consistently lower on CD4 NKT cells across all groups. The activating receptor NKG2D was significantly higher on CD4 NKT cells in all examined cohorts. These findings suggest that CD4 NKT cells tend towards a more tolerogenic phenotype, while CD4 NKT cells maintain a balanced cytotoxic potential with reduced immunoregulation function. The dynamic regulation of immune checkpoints on NKT cell subsets, particularly the downregulation of PD-L1 and CD226 in late pregnancy, highlights their fine-tuned role in balancing maternal-fetal immune tolerance with readiness for parturition.