Innate Immunity

"All animals, even those with much simpler bodies than our own, respond to tissue damage in ways that resemble inflammation in humans. They have cells similar to leukocytes and defensive proteins that flood into areas of tissue damage or infection. These leukocytes and proteins can defend the organism from pathogens because they recognize common patterns of molecules that occur in the structures of many different types of pathogens. These pathogen signature molecules are known as PAMPs, or pathogen-associated molecular patterns. The fact that PAMPs are commonly found in unrelated pathogens means that the leukocytes that recognize them cannot tell one type of pathogen from another. This non-specific immune response against pathogens is widespread among animals and is described as innate immunity. The leukocytes involved in innate immunity are of two general types, each with a different action against pathogens. Cytotoxic leukocytes attach to the outside of a pathogen and release destructive chemicals onto its surface. Worm larvae, bacteria and protists can all be killed this way. Phagocytic leukocytes, or phagocytes, engulf small pathogens such as bacteria, drawing them into the cytosol where destructive chemicals break them down. This action is termed phagocytosis. Specialized proteins are also important contributors to the innate immune response. They include proteins that accelerate inflammation, target leukocytes onto pathogens or make host cells resistant to invasion by viruses. Their concentration increases rapidly in the bloodstream during an infection, and this rise can be detected in blood tests as a diagnostic sign of infection. Innate immunity is based on cells similar to human leukocytes and defensive proteins that defend the organism against pathogens in general in a non-specific way. These defenses cannot distinguish between one type of pathogen and another."