Activation and Migration
Besides mediating uptake of antigenic material from the surrounding tissue, the PRRs also play an important role in triggering the cytokine network that will eventually influence the type of adaptive immune response that will be evoked against the pathogen. The phagocytic cells that have taken up pathogens from the infected tissue become activated and start to produce pro-inflammatory cytokines such as inter-leukin-1b, interleukin-6 and tumor necrosis factor-a as well as chemokines. The chemokines recruit more phagocytic cells such as neutrophils and monocytes to the infection site, whereas the pro-inflammatory cytokines induce fever and the production of acute-phase response proteins that can opsonize pathogens.
Most phagocytic cells, including DCs and macrophages, but also B-cells can serve as profes-sional APCs to present processed antigenic determi-nants to lymphocytes in the peripheral lymphoid organs. For instance, DCs that have taken up antigens from infected tissue become activated and migrate via the afferent lymphatic vessels towards nearby lymph nodes where the encounter with pathogen-specific lymphocytes can take place.