CD4 and COVID-19: In addition, the presence of higher amount of angiotensin-converting enzyme 2 protein receptors—SARS-COV-2 mainly attack cells via these receptors—in males [53], their lower CD4 + T cell counts, vulnerable CD8 + T cell cytotoxic activity, and a decrease in formation of immunoglobulins by B cells in comparison to females [54, 55] all increase the vulnerability of men to COVID-19.