In addition to its importance for human civilization as an industrial metal copper also plays a vital role in the immune system as a killer of foreign microbes.
S.E. Gould writing for Scientific American provides an interesting breakdown of the red metal's ability to destroy microbes and its use by the human immune system to dispatch bacterial threats.
Despite its innocuous reputation and commonplace nature copper is a toxic substance in quantities of more than an atom per cell, which accounts for its tremendous bacteria-killing capability.
According to Gould, although large amounts of copper are toxic for almost all living cells, it is this very toxicity which make the metal a vital ingredient for complex organisms such as human beings, who exploit its lethal propensity as a tool for their immune systems.
The white blood cells of the human immune system surround invading bacteria upon activation before boosting their levels of copper ions in order to break down the threatening intruders.
This is the reason that insufficient copper levels weaken the human immune system as well as increase susceptibility to sickness and infection.
Gould also notes that many pathogenic bacteria have developed copper-resistant genes, which when confronted with heightened copper levels are capable of manufacturing proteins to expel the deleterious ions.