Inflammation is the body’s response to infection and injury, its basic reaction to tissue damage. It is a protective mechanism and is part of the healing process. It can be seen as the body’s attempt to eliminate offending agents.

Inflammation can have biological (pathogens or necrotic (dead) tissue), chemical (toxic substances) or physical (extreme temperatures, trauma) causes or can be the result of abnormal immune responses (autoimmune conditions, allergic reactions).

The inflammatory process involves the host’s defence mechanism, the immune system. This is delivered by the circulatory and lymphatic system. In mammals the immune system is a sophisticated mechanism, made up of a non-specific immediate-response system (the innate immune system, which all living creatures have) and a specific-response layer which produces a delayed response.

There are advantages and disadvantages to maintaining a sophisticated immune system. It is advantageous to have an immune system that, in principle, can prevent infections by drawing on its memory functions (antibodies) and/or initiate highly specific responses to infections. It is, however, expensive (biochemically speaking) for the host system to maintain such a defence system and the complicated system is vulnerable to small errors and imbalances that can lead to profound malfunctions of the immune system.

The immune system can be under- or overactive, and there can be abnormal immune responses to the host’s own tissues (autoimmune disorders) or to foreign agents, for example pollen causing hay fever. Regular as well as abnormal immune responses can be acute or chronic. The characteristics of acute and chronic inflammatory conditions differ considerably. The chronic process begins when in the acute inflammatory phase the immune system failed to eliminate the offending agent from the body. Autoimmune disorders tend to fluctuate between acute-phase-type and chronic-phase-type behaviour.

In order to understand the purposes of different interventions aimed at moderating various different inflammatory conditions, it is necessary to first have a closer look at the complicated workings of the immune system and the cascade of inflammatory responses. Equipped with this insight, we will discuss a number of relevant inflammatory conditions and the working of medicinal drugs used to treat abnormal immune responses and other inflammatory conditions.

Next section: Inflammation