Active Immunization: Generation of an Immune Response
The generation of an immune reaction against a pathogen by vaccination follows several distinct steps that should ultimately lead to long-lasting protection against the pathogen through memory cells. These steps are uptake of the vaccine (consisting of either the entire pathogen or antigenic components thereof) by phagocytic cells, activation and migration of profes-sional antigen-presenting cells (APCs) from infected tissue to peripheral lymphoid organs, antigen pre-sentation to T-lymphocytes and finally activation (or inhibition) of T- and B-lymphocytes. The entire process is illustrated in Figure 3. Below we will describe the successive steps leading to an immune response to a pathogen, which are important for the design and fate of vaccines against the pathogen.