Publish date: 21.02.2021
Several new studies have shown that the outcome of COVID19 is worse for older male patients compared to older female patients. The authors of the study published in Science (Takehiro Takahashi and Akiko Iwasaki, “Sex differences in immune responses”, Science 2021; 371(6527), 347-348) found that males have a 1.7x higher risk of death compared to females. Scientists think the increased risk in males is because men have weaker immune response to infections than women. Immune responses vary between sexes due to differences in chromosomes, immune cell expression, and hormone levels. In males, cells contain only one copy of the X chromosome with key genes involved in regulation of the innate immune response while women have two copies of the X chromosome per cell. Although only one copy of the X chromosome per cell is active, there are cases of cells that have partial expression of the second X chromosome, which boosts the expression of immune system genes. Males also experience immune cell expression changes that lead to worse adaptive immune responses at age 62 – 64 about 5-6 years earlier than women. Another key difference between men and women lies in their estrogen hormone levels. In cell and animal models, estrogen has been found to modulate expression of angiotensin-converting enzyme 2 (ACE2), a key receptor SARS-COV-2 uses to enter the cell. Due to these immune system differences, Takahashi and Iwasaki suggest that future COVID19 infection and vaccine studies should report data for males and females separately. This will allow scientists to better understand how to treat and prevent COVID19 disease in different sex groups.