Figure 1.

T Cell-Mediated Response to Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) Infection.

Infection occurs in the patients after respiratory tract exposure. Subsequently, virus entry occurs via binding to angiotensin-converting enzyme 2 (ACE2) on the surface of various cell types and begins viral replication. Antigen-presenting cells such as dendritic cells endocytose the SARS-CoV-2 virus and degrade them through a process called antigen processing. These antigen fragments are then presented by proteins termed ‘MHC class molecules’, on the cell surface and allow recognition by a T cell. If a CD8⁺ T cell is capable of binding, it will undergo clonal expansion and directly target infected cells through either perforin/granzymes, FAS ligand/tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) pathways, or secretion of proinflammatory mediators. If the CD4⁺ T cell is capable of binding, it can activate B cells that recognize the antigen by causing them to clonally proliferate and secrete antibodies to target the SARS-CoV-2 virus. Abbreviations: BCR, B cell receptor; MHC, major histocompatibility complex; TCR, T cell receptor.