Fig. 1

Adaptive immune activation induced by NP (SAPN/VLPS) vaccines. APCs recognize and take up NP-based vaccines when they are administered. After injection, NP-based vaccines are detected and taken up by APCs, which initiates DC maturation. Furthermore, DC maturation triggers the production of TNF-α (a proinflammatory factor) and the recruitment of more APCs to boost lysosomal proteolysis in the cell. Dendritic cells (DCs) process NP-based vaccines into small peptides, to form an MHC-peptide complex with T cell receptor (TCR) on CD8⁺ and CD4⁺ T cells. CD4⁺ T cells interact with B cells, resulting in B cells being activated and then differentiating into plasma cells, which can secrete antibodies and neutralize pathogens. CD4⁺ T-cell activation can also promote the development of B cells into memory B cells. CD8⁺cytotoxic T lymphocytes (CTLs) activated by APCs proliferate and differentiate into effector and specific memory CTLs. Effector CTLs are capable of causing apoptosis via the release of cytotoxic mediators to infected cells. Image created with BioRender.com