Fig. 3
The core of the action mechanisms of adjuvants. Adjuvants are classified as immunostimulants and delivery systems. Immunostimulants such as PAMPs, DAMPs, and chemically synthesized small molecule agonists, provide danger signals (signal 0) to activate PRRs on APCs, thereby enhancing antigen presentation on MHC molecules (signal 1). In addition, activation of PRRs leads to upregulation of cytokines and co-stimulatory molecules expression, which results in enhanced co-stimulatory signaling (signal 2). Delivery systems such as LNPs, PLGA, and self-loaded protein nanoparticles, act by facilitating the presentation of antigens on MHC molecules (signal 1). This figure was created with BioRender (https://biorender.com/)
