Fig. 1.

Vaccines and immune system interaction. Vaccines either penetrate the DCs at the injection site or reach the lymph nodes, producing the S protein. In addition, innate immunity cells are activated by the vaccine’s intrinsic adjuvant power, leading to rapid secretion of IFN-1 and pro-inflammatory cytokines. TLRs, in particular, TLR-7 are activated by mRNA vaccines, while TLR-9 is the predominant receptor for AdV vaccines. DCs present the S-protein to naive T cells, through the binding of T cell receptor (TCR) to MHC-II and binding of the CD80/86 and CD28 receptors, which are thus stimulated to differentiate into cytotoxic T lymphocytes and helper T lymphocytes. Follicular T-h cells (TFH) induce B cells to differentiate into plasma cells, producing anti-S antibodies. T cells and memory B cells then come into play to prevent future SARS-CoV-2 infection. Created with BioRender.com.