CD8A and COVID-19: Another subset of proteins had a moderate to high positive correlation with activation of the adaptive immune system, i.e., higher anti-SARS-CoV-2 IgM, IgA, IgG levels, and higher percentage of activated CD8+ cells, while being at the same time associated with higher levels of ferritin, AST, ALT, and LDH, all of which have been associated with COVID-19 severity13.