*2.5. VLP Can Activate the Complement System*

Proteins on the surface of VLP, like those of the viruses from which they are derived or other pathogens, are very organized and repetitive. Hence, an active binding to natural IgM antibodies or IgG, can recruit complement component 1q (C1q) and activate the complement cascade. In addition, protein C and other pentraxins can bind to the surface of VLP, also activating the classical complement cascade, and facilitating their uptake by DCs and macrophages. After being taken up by these antigen-presenting cells (APCs), the VLP reaches the endosome-lysosome compartment and is degraded into peptides. These peptides through MHC class II molecules are carried to the cell surface and presented to CD4<sup>+</sup> T helper cells. The vaccine antigen can alternatively be presented by MHC class I molecules to induce CD8<sup>+</sup> T cell responses, an essential requirement for therapeutic vaccine's candidates [76].
