Fig. 2.

Protective and Pathologic Immunity in Coronavirus Infection: Humoral and Cellular Roles. Long-term survival and rapid proliferation with effector function on re-exposure are benchmarks of T-cells in highly effective infection- or vaccine-induced protective immunity against viral infections. Long-lifespan and maturation of CD8 T-cells is key for both quality and durability of immunity. In CoV infections, T-cells exhibit these features but antibodies and memory B-cells have not been durable. CD4 T-cells play critical helper roles for both CD8 T-cells and B-cells. Antibodies (by ADE or macrophage activation) and CD4 T-cells (by excessive cytokine production or Th2 eosinophilic immune damage) are concerns for potential contribution to tissue pathology in CoV infection. CD4 T-cells and tissue cytokines have shown a Th1 pattern in SARS-CoV-2. T-cells in CoV infections appear to have long lifespan and in both SARS-CoV-1 and -2 patients there cross-reactivity for betacoronavirus proteins. Abbreviations: CoV, coronavirus; Ab, antibodies; Ag, antigen; Cyto, cytokines; DC, dendritic cells; TCM, central memory T-cells; TRM, resident memory T-cells; T_fh, follicle helper T-cells; GC, germinal center; ADE, antibody-dependent enhancement; Fxns, functions; +, stimulatory effect.