Download Revision: The process of inflammation

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Volume 29, Number 2, November 2016
Revision
The process of inflammation
Jan Bradley and Kathryn Else
Inflammation is an acute response to invasion by pathogens, and can cause significant tissue damage
if it is not controlled. In the absence of infection or damage, tissues are healthy and uninflamed (see
Figure 1A). Upon infection, white blood cells are activated and there is an increase in the flow of blood
to the infected area. The blood vessels become ‘leaky’ (Figure 1B). Fluid and white blood cells move
out of the blood vessels into the infected tissue. The white blood cells fight the invading pathogens by
producing molecules that also cause inflammation, so the tissue is damaged further. It becomes
swollen, painful and red — inflamed. If the infection is not cleared, the inflammation escalates and
damage to cells and tissues grows, as more white blood cells accumulate, releasing inflammatory
molecules to destroy the pathogen (Figure 1C). Tissue damage also occurs if the initial response to
infection is too strong. In this case, even though the pathogen may be cleared, this is at the expense
of exposing the host’s tissues to very high levels of inflammatory molecules. Once an infection is
cleared and the pathogens killed, the blood vessels become less leaky. The white blood cells that
entered the tissue from the blood vessels die, having done their job (Figure 1D). The inflammation
dies down or ‘resolves’, and the tissue damaged during the inflammatory response can heal.
Figure 1
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