Figure 3.

Key components of the adaptive immune response to SARS-CoV-2. The adaptive immune response is activated following viral uptake and antigen processing by a range of APCs. The APCs present viral antigen to B cells which then differentiate into antibody producing plasma cells. The neutralizing antibodies (nAbs) then bind to key viral proteins, such as the spike protein, and neutralize their activity. Other Ab-mediated antiviral functions include antibody dependent cellular cytotoxicity (ADCC), antibody dependent cellular phagocytosis (ADCP), and antibody dependent complement activation (ADCA). Cytotoxic CD8⁺ T cells kill virally infected cells via the production of granzymes and perforin and the expression of Fas ligand (FasL), all of which mediate cellular apoptosis. A series of CD4⁺ T cell populations are involved in the adaptive cellular response to SARS-CoV-2. Follicular helper T cells (T_FH) and Th2 CD4⁺ T cells both provide help for B cell antibody production. Th1 and Th17 CD4⁺ T cells are also thought to play a role in the inflammatory response and viral killing. CD4⁺ regulatory T cells have been implicated with an immunoregulatory role in SARS-CoV-2 infection via the production of anti-inflammatory cytokines and contact-mediated cellular suppression. Whether CD8⁺ Tregs and Bregs play a role is not currently known.