Figure 2.

Schematic overview of the working principle of mRNA vaccines to protect against COVID-19. A. The mRNA encoding the S protein is encapsulated in a lipid nanoparticle and injected intramuscular in the deltoid muscle of the shoulder. B. Production of the S protein antigen: The mRNA provides the template to produce the S protein in cells that were reached by lipid nanoparticles, which are likely muscle tissue (site of injection), nearby lymphatic tissue and spleen tissue (with immune cells) as well as liver tissue. C. Activation of the immune response: Antigen (S protein) recognition on cell surfaces induces expression of effector molecules (interleukins) by T cells, which activates B cells, leads to B cell proliferation and subsequent B cell differentiation. D. Antibody production and long-term immunization: B cells differentiate to antibody-secreting plasma cells (antibodies target the S protein) and resting memory B cells, which enable a faster antibody production in future infections. (created with BioRender.com)