A group from Peking Union Medical College, etc. has reported on differences in SARS-CoV-2 infectivity between M1 macrophages and M2 macrophages including alveolar epithelial type II (AT2) cells.
https://www.nature.com/articles/s41421-021-00258-1
Generally speaking, M1 macrophages are inflammatory and M2 macrophages are anti-inflammatory. Comparing AT2, M1 macrophages, and M2 macrophages, SARS-CoV-2 infection and its replication was higher in macrophages than AT2, M1 macrophages took up SARS-CoV-w2 with higher efficiency than M2 macrophages, and the viral loads increased in an exponential fashion in M1 macrophages but in a flat fashion in M2 macrophages. It is considered that ACE2 could be the receptor that mediates the infection with SARS-CoV-2, and ACE2 has been reported to be expressed also by macrophages. However, there were no difference in the infectivity between ACE2-overexpressing macrophages and ACE2-knockeddown macrophages. So, virus takeup through phagocytosis could initiate SARS-CoBV-2 infection.
Authors related the difference in the infectivity between M1 and M2 to difference in cell softness, endosomal, and lysosomal pH.
