Inflammation

If the skin is cut (see Chapter 23) then chemicals are released from the damaged tissue; these initiate an inflammatory response (Fig. 24.1). Inflammation can be identified by four cardinal signs:

Fig. 24.1 Non-specific defences.

The outcome of the inflammatory response is that vasodilation (swelling of blood vessels) takes place. This increases their permeability, and macrophagocyte cells migrate to the site of the injury. The macrophagocyte cells include monocytes and neutrophils and these are responsible for ingesting foreign bodies and destroying them. The inflammatory response is also necessary for the initiation of wound healing (see Chapter 23). The basophil cells, which are called mast cells when they are in the skin, play a part in this inflammatory response by releasing histamine, which leads to inflammation.

A collection of white cells at a site of injury can be recognized as the white material pus, which is a collection of dead cells and fluid. In some cases of injury and inflammation the body temperature can rise for prolonged periods above normal body temperature, and this is called pyrexia. While pyrexia can be very uncomfortable and even dangerous if too prolonged, it is a response of the body aimed at speeding up all the processes that deal with invasion by foreign matter.

Cells of the non-specific defences, along with T lymphocytes, play a role in the immune system as antigen-presenting cells. By ingesting foreign bodies the antigen-presenting cells subsequently display parts of these foreign bodies or antigens on their surface, at the outside of the plasma membrane, and these are part of the process that triggers the immune system.

The immune system

There are two types of immunity: