CD40LG and COVID-19: Investigations into the mechanisms by which complement activation occurs in COVID-19 revealed (1) the receptor-binding domain of the spike protein of SARS-CoV-2 binds to specific IgG/IgM antibodies, (2) heparan sulfate binds to the spike protein of SARS-CoV-2, and (3) recognition of the spike and nucleocapsid proteins of SARS-CoV-2 by lectin pathway components subsequently triggers complement activation by the classical, alternative, and lectin pathways [32,35,242,243,244].