Overview Introduction The human immune system is designed to deal with a variety of insults including acute exposure to new infectious agents such as bacteria and viruses re-exposure to the same infectious agent after clearance of the initial infection chronic infection by fungi and parasites In order to have a variety of responses to infection, the immune system is divided into the innate immune system that is responsible for fast recognization and clearance of initial infections destruction of fungi and parasites the adaptive immune system that is responsible for immunological memory and rapid responses to re-infection recognition of pathogens that have defences against innate immunity Differences Between Innate and Adaptive Immunity Differences Between Innate and Adaptive Immunity Feature Innate Immunity Adaptive Immunity Genetics All components encoded in germline May vary between individuals but does not change over course of an individual lifetime Inherited from parents Encoded as variable V, D, and J regions Immunity is generated by recombination of these regions and further hypervariation Not inherited from parents Components Myeloid lineage white blood cells such as neutrophils monocytes macrophages Natural killer (NK) cells Complement system Physical barriers (such as mucus membranes) Killer CD8+ T-cells Helper CD4+ T-cells B-cells Antibodies Recognition Uses receptors that recognize conserved pathogen-associated molecular patterns (PAMPs) Examples linclude LPS flagellin nucleic acids Uses recombined B- and T-cell receptors that recognize specific antigens on pathogens Can recognize aspects of almost all pathogens Response Nonspecific recognition Occurs rapidly from minutes to hours Does not confer memory Specific recognition that can be refined Occurs over days to years Confirms immunological memory Resistance Caused by pathogenic virulence factors Often involves disabling the conserved pattern recognition used by innate system Caused by mutation of the recognized antigen Can be overcome by further maturation of the receptor Interactions between Innate and Adaptive systems These two branches of the immune system can cooperate in several ways including opsonization coating pathogens with antibodies in order to activate antibody dependent cellular cytotoxicity antibody dependent cellular phagocytosis complement activation activation of the C3 convertase by the classical complement pathway interaction of antibodies with C1q cytokine secretion release of signaling molecules by helper T-cells causes additional production of innate immune cells synthesis of circulating factors such as the complement system