Page 196 - Veterinary Immunology, 10th Edition

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FIG. 7.5 The role of hepcidin in regulating iron availability. This
protein prevents iron efflux from enterocytes and macrophages by
binding to ferroportin and triggering its degradation. The net effect is
to retain iron within these cells, making it unavailable for hemoglobin
synthesis and leading to the development of anemia.

Most pathogenic bacteria, such as Staphylococcus aureus,

Escherichia coli, Bacillus anthracis, Pasteurella multocida, and
Mycobacterium tuberculosis, require iron for growth since iron forms
the key catalytic site in many of their enzymes. Animals, however,
also require iron for vital functions such as oxygen transport and

energy production. As a result, bacteria and their hosts compete for
the same metal. The result of this competition may determine the
outcome of an infection.
Free iron concentrations within animal tissues are normally very

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low. Mammalian blood has just 10 M free iron since almost all of
the available iron is bound to proteins. These iron-binding proteins
include transferrin, lactoferrin, hepcidin, siderocalin, haptoglobin,
and ferritin.

Iron is usually absorbed from food by duodenal enterocytes. It
binds to a cell surface iron carrier called ferroportin and is
transported to the bloodstream where it is bound by transferrin.
Most of this iron is incorporated into hemoglobin in red cells. Less

than 10% of our daily needs, however, are met by importing dietary
iron. Most is derived by recycling aged or damaged red cells. Aged
red cells give up their iron when ingested by splenic macrophages.
The macrophages phagocytose these cells and catabolize the
hemoglobin using hemoxygenase. They release the iron obtained

from hemoglobin into the circulation via ferroportin. The exported

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