Figure 4.

Overview of immune response elicited by various vaccine candidates. When administered into skin or muscle cells (A), the nucleic acid expresses and codes for an immunogenic protein that mimics viral infection (B). (C–E) Humoral responses: Antigens produced by skin/muscle cells are released in blood to activate the antibody response; antigen recognition by naïve B cells (C) leading to clonal selection and plasma cell (antibody secreting B cells) formation (D) and eventually production of long-lasting memory B cells (E). (F) Antigen processing and presentation: The antigen produced by skin/muscle cells are captured by antigen-presenting cells (APCs; dendritic cells or macrophages) for processing and presented by MHC-II or MHC-I molecules on their surface. (G–I) CD4⁺T helper cells effector and memory response: The presented MHC-II molecule and antigen complex on APCs recognized by TCR and CD4 molecules on CD4⁺ Th cells (G) leading to production of effector CD4⁺ Th cells (H), which produce sufficient levels of cytokines (Th2 cells produce TH2 cytokines IL-4 or IL-10 for humoral response and Th1 cells produce IL-12, IFN-Y for CTL response), and eventually, long-lasting memory CD4⁺ cells are generated (I). (J–L) CD8⁺T helper cells effector and memory response: The presented antigen and MHC-II molecule complex on APCs recognized by TCR and CD8 molecules on CD8⁺ T cells (J) leading to production of effector CD8⁺T cells also known as cytotoxic T lymphocytes (CTL), which are responsible for killing the infected or self-altered cells (K), and finally, long-lasting memory CD8⁺T cells are generated (L). All memory cells provide long-lasting, heightened, and antigen-specific responses upon future infections.