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Complement proteins are proteins that play a role in the non-specific immune responses alongside these non-specific immune cells to make up the first line of immune defense. [4] The non-specific immune response is an immediate antigen-independent response, however it is not antigen-specific. Non-specific immunity results in no immunologic memory.
Rather, NK cells destroy compromised host cells, such as tumor cells or virus-infected cells, recognizing such cells by a condition known as "missing self". This term describes cells with abnormally low levels of a cell-surface marker called MHC I ( major histocompatibility complex ) - a situation that can arise in viral infections of host ...
Besides phagocytosis, they play a critical role in nonspecific defense (innate immunity) and also help initiate specific defense mechanisms (adaptive immunity) by recruiting other immune cells such as lymphocytes. For example, they are important as antigen presenters to T cells.
Scheme of the complement system. The complement system, also known as complement cascade, is a part of the humoral, innate immune system and enhances (complements) the ability of antibodies and phagocytic cells to clear microbes and damaged cells from an organism, promote inflammation, and attack the pathogen's cell membrane. [1]
Innate immune defenses are non-specific, meaning these systems respond to pathogens in a generic way. [19] This system does not confer long-lasting immunity against a pathogen. The innate immune system is the dominant system of host defense in most organisms, [2] and the only one in plants. [20]
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.
In general, this results in the uptake (internalization, phagocytosis) of bound molecules by endosomes/phagosomes and in cellular activation; thus such elements of innate immunity as macrophages, PMNs and dendritic cells assume functions of nonspecific immune defense, B1a and MZ B cells form the first antibodies, and specific antibody formation ...
Dendritic cells are specialized antigen-presenting cells that have long outgrowths called dendrites, [87] that help to engulf microbes and other invaders. [ 88 ] [ 89 ] Dendritic cells are present in the tissues that are in contact with the external environment, mainly the skin, the inner lining of the nose, the lungs, the stomach, and the ...