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The immune system is a network of biological systems that protects an organism from diseases. It detects and responds to a wide variety of pathogens , from viruses to bacteria , as well as cancer cells , parasitic worms , and also objects such as wood splinters , distinguishing them from the organism's own healthy tissue .
An immune response is a physiological reaction which occurs within an organism in the context of inflammation for the purpose of defending against exogenous factors. These include a wide variety of different toxins, viruses, intra- and extracellular bacteria, protozoa, helminths, and fungi which could cause serious problems to the health of the host organism if not cleared from the body.
An individual's immunity can be acquired via a natural infection or through artificial means, such as vaccination. [51] When a critical proportion of the population becomes immune, called the herd immunity threshold (HIT) or herd immunity level (HIL), the disease may no longer persist in the population, ceasing to be endemic. [5] [26]
Immunology is a branch of biology and medicine [1] that covers the study of immune systems [2] in all organisms.. Immunology charts, measures, and contextualizes the physiological functioning of the immune system in states of both health and diseases; malfunctions of the immune system in immunological disorders (such as autoimmune diseases, hypersensitivities, [3] immune deficiency, [4] and ...
The human immune system relies on a plethora of cell-cell signaling pathways to transmit information about a cell's health and microenvironment. Many of these pathways are mediated by soluble ligands, cytokines, that fit like a lock-and-key into adjacent cell surface receptors.
A representation of the cholera epidemic of the 19th century. For thousands of years mankind has been intrigued with the causes of disease and the concept of immunity. The prehistoric view was that disease was caused by supernatural forces, and that illness was a form of theurgic punishment for "bad deeds" or "evil thoughts" visited upon the soul by the gods or by one's enemies. [8]
Cellular immunity, also known as cell-mediated immunity, is an immune response that does not rely on the production of antibodies. Rather, cell-mediated immunity is the activation of phagocytes , antigen-specific cytotoxic T-lymphocytes , and the release of various cytokines in response to an antigen .
The innate immune system or nonspecific immune system [1] is one of the two main immunity strategies in vertebrates (the other being the adaptive immune system). The innate immune system is an alternate defense strategy and is the dominant immune system response found in plants , fungi , prokaryotes , and invertebrates (see Beyond vertebrates ).