How does the innate immune system function?
The first line of defense that the innate immune system includes are the barriers between cells. The barrier between cells prevents pathogens from entering the body. The vast majority of pathogens are stopped at this barrier and the other mechanisms that the innate immune system has at its disposal are not required. This barrier can also include the cilia and the peristaltic movement of the respiratory tract and the gastrointestinal tract. The desquamation of the epithelium of the skin also acts to remove pathogenic agents and bacteria that may have adhered to the surfaces of various epithelium. Flushing of tears and saliva also help to prevent infection (though these methods often include antibodies produced by the adaptive immune system.
The first response that is generally used by the innate immune system to fight infection is inflammation. Inflammation is created by chemicals that are released by injured cells and some of the cells of the immune system and typically serves two purposes: to act as a barrier against infection and to promote healing of damaged tissue once the infection is over. Often, inflammation is cause by factors that are released by the cells of the innate immune system (macrophages, histiocytes, mastocytes, etc.). These cells release chemokines and cytokines in order to sensitize pain receptors in the area, attract other immune cells, trigger the adaptive immune system, attract phagocytes and neutrophils, and increase vasodilation of blood vessels. The main symptoms involved in inflammation are heat, swelling, pain, and redness.
Beyond inflammation, the innate immune system triggers a complex series of chemical reactions known as the complement cascade. This cascade complements the other effects of the immune system and aids immune cells in clearing out pathogens. Once the first proteins of the cascade are triggered, they are broken apart and attract more proteins of the cascade and begin a full series of reactions that result in the peppering of pathogens by proteins (opsonization), cytolysis of the cell membrane of the pathogen, neutralization of antigen-antibody complexes, and help attract other immune cells. This system (or a system very similar to it) is nearly ubiquitous across vertebrate species and can even be found in invertebrates.
The innate immune system is the first line of defense against infection. It is characterized by a non-specific response and lack of immunological memory. The response that it offers to infection is also very rapid, as opposed to the slow and specific response that is mounted by the adaptive immune system. Cells of the innate immune system include NK cells (natural killer cells), eosinophils, phagocytic cells, dendritic cells, and mast cells (which usually function to release histamines and other cytokines). One of the most important functions of the innate immune system, aside from defense, is to provide the adaptive immune system with information about the type of infection that the body is facing so that the adaptive immune system can begin to mount its own response.
Written By : Alexander Maness, United States (M.S. in Biotechnology)
Edited by: Rajesh Bihani ( Find me on Google+ )