Investigation of immune checkpoint molecules (CTLA-4, PD-1, PD-L1, Tim-3) expressions in preeclampsia: A comparative study of membranous and soluble forms

Preeclampsia (PE) is characterized by immune dysfunction, including altered expression levels of multiple immune checkpoints (ICs), which are essential for inducing immune tolerance during pregnancy. While the pivotal role of ICs in PE is well-established, a limited understanding remains of the changes in their various forms, particularly in their membranous and secretory states. This study focused on exploring the probable role of ICs in the pathophysiology of PE via measuring the levels of their transmembrane and soluble forms. Initially, expression levels of transmembrane CTLA-4, PD-1, PD-L1, and Tim-3 on PBMCs of PE patients were assessed through qRT-PCR and western blot analysis. Additionally, ELISA was performed to evaluate their soluble forms in serum. Finally, the correlation between transmembrane and soluble forms was determined. PE patients exhibited decreased CTLA-4, PD-1, and Tim-3 expression, while PD-L1 was increased compared to the healthy group. sCTLA-4 and sPD-L1 were reduced in serum; however, sPD-1 and sTim-3 were increased. The expression of CTLA-4 on PBMCs was positively correlated with sCTLA-4. Meanwhile, PD-1, PD-L1, and Tim-3 expressions were negatively correlated with soluble forms. The observed abnormal expression levels of transmembrane CTLA-4, PD-1, PD-L1, and Tim-3 on PBMCs, along with their soluble counterparts in serum, indicate their possible role in the pathogenesis of PE. Thus, variations in these ICs' expression could enhance the differentiation of PE and aid in developing targeted therapeutic strategies.