Evidence of Placental Villous Inflammation and Apoptosis in Third-Trimester Symptomatic SARS-CoV-2 Maternal Infection

Abstract

Purpose: In view of conflicting reports on the ability of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) to infect placental tissue, this study aimed to further evaluate the impact of inflammation and placental damage from symptomatic third-trimester maternal COVID-19 infection.

Materials and methods: This case-control study included 32 placenta samples each from symptomatic COVID-19 pregnancy and normal non-COVID-19 pregnancy. The villous placental area's inflammatory expression [angiotensin converting enzyme-2 (ACE-2), transmembrane protease serine-2 (TMPRSS2), interferon-γ (IFN-γ), interleukin-6 (IL-6), and SARS-CoV-2 spike protein] and apoptotic rate were examined using immunohistochemistry and Terminal deoxynucleotidyl transferase dUTP Nick-End Labeling (TUNEL) assay. Comparison and correlation analysis were used based on COVID-19 infection, placental SARS-CoV-2 spike protein evidence, and maternal severity status.

Results: Higher expressions of TMPRSS2, IFN-γ, and trophoblast apoptotic rate were observed in the COVID-19 group (p<0.001), whereas ACE-2 and IL-6 expressions were not significantly different from the control group (p>0.05). Additionally, SARS-CoV-2 spike protein was detected in 8 (25%) placental samples of COVID-19 pregnancy. COVID-19 subgroup analysis revealed increased IFN-γ, trophoblast, and stromal apoptosis (p<0.01). Moreover, the results of the current study revealed no correlation between maternal COVID-19 severity and placental inflammation as well as the apoptotic process.

Conclusion: The presence of SARS-CoV-2 spike protein as well as altered inflammatory and apoptotic processes may indicate the presence of placental disturbance in third-trimester maternal COVID-19 infection. The lack of correlation between placental disruption and maternal severity status suggests the need for more research to understand the infection process and any potential long-term impacts on all offsprings born to COVID-19-infected pregnant women.

Keywords: COVID-19; apoptosis; inflammation; placenta; pregnancy.

Fig. 1. Study design. SARS-CoV-2, severe acute respiratory syndrome coronavirus-2; ACE-2, angiotensin converting enzyme-2; TMPRSS2, transmembrane protease serine-2; IFN-γ, interferon-γ; IL-6, interleukin-6.

Fig. 2. Immunohistochemical characteristics (with 400× magnification) and their expressions on (A) ACE-2, (B) TMPRSS2, (C) IFN-γ, (D) IL-6, and (E) trophoblast and stromal apoptosis between COVID-19 and normal placenta (thin arrow: trophoblast expression, thick arrow: stromal expression). ACE-2, angiotensin converting enzyme-2; TMPRSS2, transmembrane protease serine-2; IFN-γ, interferon-γ; IL-6, interleukin-6.

Fig. 3. Immunohistochemical image of the SARS-CoV-2 spike protein on COVID-19-infected placenta (thin arrow) with box-plot comparison of the spike protein-positive and spike protein-negative subgroups in the COVID-19 placenta for ACE-2, TMPRSS2, IFN-γ, IL-6, trophoblast-stromal apoptosis expression, and perinatal outcome (birthweight, Apgar score 1 minute and 5 minutes). SARS-CoV-2, severe acute respiratory syndrome coronavirus-2; ACE-2, angiotensin converting enzyme-2; TMPRSS2, transmembrane protease serine-2; IFN-γ, interferon-γ; IL-6, interleukin-6.