User:Simon C Andrews

I am a molecular microbiologists at the University of Reading, and so have interests in various aspects of bacteriology. I am composing this page as part of a Wikipedia training event.

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Iron withholding

Iron withholding (or iron withdrawal) is a component of the innate immune system of humans and many other animals. The process involves the deliberate lowering of levels of available iron in tissue fluids (such as blood) in order to limit the growth of invasive microbes that might have the potential to cause disease. Since nearly all organisms, including pathogenic microbes, have an absolute requirement for iron, this acts as an effective strategy for limiting or preventing microbial growth within the host. This approach is only effective for pathogens that are extracellular since intracellular pathogens are considered to have ready access to iron from intracelluar sources. The iron withholding strategy is the major contributor to 'nutritional immunity' which refers to the host's attempt at preventing the growth of invading microbes by withdrawal of any nutrient (zinc and manganese, in addition to iron, are also subject to a nutritional immunity response).

In humans, iron withholding is largely dependent on the serum glycoprotein transferrin that transports iron between tissues. Transferrin is a monomer of approximately 80 kDa, normally present in serum at around 2-3 mg/ml. Each transferrin molecule has the capacity bind two ferric iron atoms with high affinity (association constant of 1020 M at pH 7.4). However, in practice transferrin is only around 30% saturated with iron so maintains a high capacity for sequestering additional iron. This

''in progress............. to provide an article for a term that does not currently have a wikipedia page''