These patients with long Covid had higher IgG reactivity to RBD, NP, and S1-S2 antigens and more up-regulated expression of Fas, OX40, CD154, LAG-3, TIGIT in CD4+ T cells and CD69, Fas, CD137, LAG-3 in CD8+ T cells compared to uninfected controls, asymptomatic patients, and patients with mild and moderate COVID-19 (figs. Here, CD4 is linked to COVID-19.