The immune response to an infection can be divided into the innate and adaptive phases that act in synergy to eliminate pathogens. Activation of the innate immune system following antigen detection results in rapid elimination of pathogen and prevention of infection. In contrast, the adaptive immune response develops after a time lag, but results in the activation of cells that are highly specific and effective in eliminating the pathogen. The quality and magnitude of the adaptive immune response is dependent on the innate immune response.Cells involved in the innate immune response include natural killer (NK) cells, natural interferon producing cells (NIPC), dendritic cells and macrophages. Many innate immune cells possess pattern recognition receptors (PRRs) such as toll-like receptors (TLR) that detect molecular signatures in pathogens resulting in antigen recognition and presentation. After recognition of antigen, cells of the innate immune system reciprocally activate one another as well as cells of the adaptive immune system like the T and B lymphocytes.
Dendritic cells are considered to be the link between the innate and adaptive immune responses. In their immature state, DCs are good detectors of antigen, but poor presenters of antigen to T cells and B cells. However, after detection of antigen via TLRs, DCs mature into efficient antigen presenting cells secreting several cytokines such as type I interferons, IL-12, IL-15 and chemokines such as IL-8 and macrophage inflammatory protein 1 (MIP1). These soluble mediators as well as cell-cell interactions result in the activation of T and B lymphocytes and thus the development of cellular and humoral adaptive immune responses.
This pathway highlights the different modes of cross talk between the innate and adaptive immune systems namely via soluble factors (chemokines and cytokines) and cell-to-cell communication.