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Aim of Review: Studies have been published in the field of innate system and microbial invasion but much is not know on the mechanisms involved. This review is organized into areas of components and function of the immune system, microbial detection, cells of the innate immune system and homeostasis.
Findings: The innate immune system activates and instructs adaptive immune responses, regulates inflammation, and mediates immune homeostasis which is the balance between opposing pro inflammatory and anti-inflammatory processes. The cells of the innate immune system use pattern recognition receptors (PRRs), which recognize pathogen-associated molecular patterns (PAMPs) on microorganisms, and communicate through cytokines. Activation of the innate immune system begins with resident cells such as the macrophages, epithelial cells and mast cells in the tissues at the site of the infection. If the threat of infection accelerates, these cells recruit other cells such as the neutrophils, NK cells, dendritic cells, monocytes and platelets from the circulation into the inflamed tissues. Many of the same cells and mechanisms used to recognize and attack microbes and initiate inflammatory reactions are also used to clear away damaged and dying cells and down regulate inflammation to maintain homeostasis within the host.
Conclusion: The innate immune system refers to germline defense mechanisms that are directed against molecular components found only in microorganisms. These mechanisms are not learned, adapted, or permanently heightened as a result of exposure to microorganisms, although they are refined by evolution over generations.
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