Figure 1.

Vaccine types, delivery devices, and immune response outcomes. A) A pictorial representation of different vaccines and delivery devices. Biological delivery systems include avirulent and attenuated recombinant bacterial vectors capable of delivering genetic and protein antigens. Traditional whole cell vaccines, such as the live attenuated vaccine depicted, contain weakened versions of pathogens that do not cause disease but can continue to replicate. Unlike whole cell vaccines, subunit vaccines only contain the most antigenic regions of a pathogen. Liposomes, a type of chemical delivery system, can provide a high degree of multivalent surface antigens. B) Diagram representing the processing and presentation of antigens in dendritic cells (DCs). Pattern recognizing receptors on the surface of DCs identify pathogen associated molecular patterns (PAMPs) which initiate DC activation. Exogenous antigens are internalized by DCs and processed in endocytic vesicles before being loaded onto MHC Class II molecules, forming a peptide-MHC II complex that is presented to immature T cells that can then stimulate either a humoral or cell-mediated (CTL, cytotoxic T cell; NK, natural killer cell) response. Endogenous, as well as exogenous, antigens can also be loaded onto MHC I molecules; the resulting complex then interacts with CD8⁺ T cells, which have cytotoxic activity.