Hofbauer Cells and COVID-19 in Pregnancy Molecular Pathology Analysis of Villous Macrophages, Endothelial Cells, and Placental Findings From 22 Placentas Infected by SARS-CoV-2 With and Without Fetal Transmission

Context.-SARS-CoV-2 can undergo maternal-fetal transmission, heightening interest in the placental pathology findings from this infection. Transplacental SARS-CoV-2 transmission is typically accompanied by chronic histiocytic intervillositis together with necrosis and positivity of syncytiotrophoblast for SARS-CoV-2. Hofbauer cells are placental macrophages that have been involved in viral diseases, including HIV and Zika virus, but their involvement in SARS-CoV-2 is unknown. Objective.-To determine whether SARS-CoV-2 can extend beyond the syncytiotrophoblast to enter Hofbauer cells, endothelium, and other villous stromal cells in infected placentas of liveborn and stillborn infants. Design.-Case-based retrospective analysis by 29 perinatal and molecular pathology specialists of placental findings from a preselected cohort of 22 SARS-CoV-2- infected placentas delivered to pregnant women testing positive for SARS-CoV-2 from 7 countries. Molecular pathology methods were used to investigate viral involvement of Hofbauer cells, villous capillary endothelium, syncytiotrophoblast, and other fetal-derived cells. Results.-Chronic histiocytic intervillositis and trophoblast necrosis were present in all 22 placentas (100%). SARS-CoV-2 was identified in Hofbauer cells from 4 of 22 placentas (18.2%). Villous capillary endothelial staining was positive in 2 of 22 cases (9.1%), both of which also had viral positivity in Hofbauer cells. Syncytiotrophoblast staining occurred in 21 of 22 placentas (95.5%). Hofbauer cell hyperplasia was present in 3 of 22 placentas (13.6%). In the 7 cases having documented transplacental infection of the fetus, 2 (28.6%) occurred in placentas with Hofbauer cell staining positive for SARS-CoV-2. Conclusions.-SARS-CoV-2 can extend beyond the trophoblast into the villous stroma, involving Hofbauer cells and capillary endothelial cells, in a small number of infected placentas. Most cases of SARS-CoV-2 transplacental fetal infection occur without Hofbauer cell involvement. (Arch Pathol Lab Med. 2021;145:1328-1340 ; doi: 10.5858/arpa.2021-0296-SA)

Automated summary

The study found that SARS-CoV-2 can extend beyond the syncytiotrophoblast to enter other villous stromal cells in the placenta, including Hofbauer cells and capillary endothelial cells. Infection of Hofbauer cells and villous capillary endothelial cells in the placenta is uncommon.