Immune checkpoints TIM-3 and Gal-9 are upregulated in male placentas with acute SARS-CoV-2 infection

New data indicate an increased risk of obstetric complications after Covid-19, the aim of this study was therefore to investigate the expression of immune checkpoint molecules TIM-3 and Gal-9 in tissue sections of placenta from patients with acute Covid-19, from patients after Covid-19 infection and from healthy controls. We used a total of 60 placentas from women who had given birth to female or male children at Augsburg University Hospital, Germany. We examined 10 placentas each with acute Covid-19 from female and male fetuses, 10 placentas each from female and male fetuses after acute Covid-19 and 10 placentas each from female and male fetuses of a healthy control group. Immunohistochemical staining against TIM-3 and Gal-9 was performed, and marker expression was assessed by an immunoreactive score (IRS). The identity of cells expressing TIM-3 or Gal-9 was then analyzed by double immunofluorescence analysis. TIM-3- and Gal-9 positive macrophages are significantly upregulated in the decidua of female acute Covid-19 placentas. TIM-3 is significantly up-regulated in male extravillous trophoblast cells in the acute phase of Covid-19. On the other hand, TIM-3 was significantly downregulated in Hofbauer cells from male placentas after Covid-19. Gal-9, the ligand for TIM-3, was significantly downregulated in Hofbauer cells from male placentas after Covid-19. Triple immunofluorescence analysis showed that male acute Covid-19 Hofbauer cells (analyzed by CD163 staining) were positive for both TIM-3 and Gal-9. Surprisingly, the observed effects were related to fetal sex. In particular, the formative effect of this infection needs to be analyzed in further studies.