Human samples
Pregnant women who had suffered PTLI from September,2018 to September,2020 in the First Affiliated Hospital of Chongqing Medical University were enrolled as study group-PTLI group, while those who had term labor at the parallel period were randomly selected as control group-TL group. Preterm labor and term labor were defined according to the guidelines of the American College of Obstetricians and Gynecologists. The criteria of infection was based on the following items: temperature >37.6 centigrade, white cell count >15*10^9/L, C-reactive protein >10 mg/L, or histological signs of chorioamnionitis[15]. Those patients with pregnancy complications such as pregnancy hypertension, intrahepatic cholestasis of pregnancy, placenta abruption and chronic diseases were excluded. Human FMs were collected within 30 minutes after delivery. These samples were stored as required for westen blot, real-time quantitative PCR (qPCR) and immunohistochemistry (IHC). The patients’ informed consent was obtained, and ethics approval was gained from the Ethics Committee of the First Affiliated Hospital of Chongqing Medical University (2019-137).
Mouse Models
IL-27Rα knock out (IL-27Rα-/-) mice on C57BL/6 background were purchased from Jackson Laboratory in the USA, and C57BL/6 mice purchased from experimental animal center of Chongqing medical university were designated as wild type (WT) mice. The absence of IL-27Rα gene was confirmed by gene identification test with mice’s tail. All mice were housed under specific pathogen free conditions during the whole course of the study. Two female mice (8-12 weeks) were mated with one male of the same genotype at dawn. The vaginal plugs were checked the next morning, whose presence indicated gestational day of 0.5. The mice model of PTLI was established as previously reported[16, 17]. Briefly, at gestational day of 16.5, the pregnant mice were intraperitoneally administered with LPS (25μg in 200μl PBS) or PBS 200μl. Then, these mice were sacrificed and gestational tissues including fetal membrane, uterus myometrium, and decidua were harvested 6 hours after LPS/PBS injection. All human and animal experiments were approved by the Clinical Research Ethics Committee of the First Affiliated Hospital of Chongqing Medical University (2019-137).
Extraction of total RNA and qPCR
Total RNA was extracted by RNAiso Plus (Takara Bio Inc., Tokyo, Japan), followed by reverse transcription using a PrimeScript RT Reagent Kit (Takara Bio Inc., Tokyo, Japan). Thereafter, generated cDNA from 1 ug RNA was subjected to real-time PCR analysis with SYBR Premix Ex Taq II kit (MCE, Shanghai, China), using thermal cycler dice real time system. Relative quantity of target gene expression to β-actin gene were calculated with comparative threshold cycle (CT) method, and primers for each target gene were presented in Sup Table 1.
Western Blot
Total protein was harvested from human FMs by RIPA lysis buffer (ZSGB-BIO, Beijing, China) containing PMSF (ZSGB-BIO, Beijing, China). Equal amount of protein (40 μg) was electrophoresed on 10% SDS-polyacrylamide gels (Invitrogen) and blotted onto PVDF membranes. The membranes were incubated overnight with IL-27Rα (1:1000, Affinity, Jiangsu, China) antibody after blocked in 5% nonfat milk for 2 hours. Then, the PVDF membranes were incubated with an HRP-conjugated anti-IgG secondary antibody, followed by band detection with an ECL chemiluminescent detection system. The blots were imaged and quantified using ImageJ software, and the results were reported as IL-27Rα/β-actin ratio.
Hematoxylin and eosin (H& E) staining and immunohistochemistry (IHC)
For H& E staining, paraffin sections were stained with hematoxylin and eosin. For IHC, following dewaxing and rehydration, microwave antigen retrieval on paraffin sections was performed. Nonspecific staining was blocked with 3% H2O2, followed by nonimmune block with 10% normal goat serum. Then, tissue sections were incubated with primary antibodies overnight at 4 centigrade (IL-27Rα 1:200,Santa Crue, China; MPO 1:300, protein-tech, China; Ly6g:1:200, protein-tech, China). After thorough washes, the sections were incubated with biotinylated goat anti-mouse/Rabbit IgG. Positive antibody binding was detected with diaminobenzidine, followed by hematoxylin staining. The cells positive for each biomarker in gestational tissues were enumerated on three fields at x400 magnifications. All measurements were carried out by two independent researchers without knowing the experimental protocols in advance.
Statistical Analysis
Statistical analysis was performed by Prism software. Student’s t test or Mann–Whitney U test were used to assess continuous variables according to its distribution. Chi-square test was used to assess categorical variables. P value< 0.05 was considered statistically significant.