Objective To analyze the expressions of programmed cell death protein 1 (PD‑1) and T cell immunoreceptor with Ig and ITIM domains (TIGIT) on decidual tissue CD4+ T lymphocytes and their correlation with the occurrence of unexplained recurrent miscarriage (URM). Methods Six patients with URM (the URM group) and six normal pregnant women (NP group) who requested artificial abortion of unintended pregnancy during the same period were enrolled. Real‑time fluorescence quantitative PCR and Western blot were adopted to detect the mRNA and protein expressions of PD‑1 and TIGIT in decidual tissue. Flow cytometry was used to detect the cell proportion of PD‑1 and TIGIT among decidual tissue CD4+ T lymphocytes and their various subsets (Th1, Treg, Th2, Th17). Spearman correlation test was used to analyze the correlations between the expressions of TIGIT and PD‑1 on decidual CD4+ T lymphocytes and the proportions of their various subsets. Results Compared with the NP group, the URM group exhibited increased mRNA and protein expressions of PD‑1 and TIGIT in decidual tissue, as well as increased proportions of CD4+TIGIT+ T lymphocytes, CD4+PD‑1+TIGIT+ T lymphocytes, and Th1 cells (P<0.05). However, there was no statistically significant difference in the proportions of CD4+PD‑1+ T lymphocytes, Treg, Th2, or Th17 cells between the two groups (P>0.05). The proportion of CD4+TIGIT+ T lymphocytes positively correlated with the proportion of Th1 cells (P<0.05), whereas it has no significant correlation with the proportions of Treg, Th2, or Th17 cells (P>0.05). The proportion of CD4+PD‑1+ T lymphocytes interpreted no significant correlation with the proportions of Th1, Treg, Th2, or Th17 cells (P>0.05). Conclusion Up-regulated expression of PD‑1 and TIGIT in decidual tissue of URM patients may disrupt maternal‑fetal immune tolerance by promoting the differentiation of CD4+ T lymphocytes toward the Th1 subset, thereby participating in the pathogenesis of URM.

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