An inflammation is a manifestation of the immune system's response to an invading organisms or substances.  These may be viruses, bacteria, fungi, allergens, or, in the case of autoimmune diseases, the bodies own tissue. A typical example of inflammation that most people are familiar with is the painful red swelling associated with acne.

When an invading organism (pathogen) is first recognised the immune system launches a response involving a number of different white blood cells (leukocytes) - this is known as an immune cascade.

At the site of the infection, there are a number of physiological changes that take place to assist the destruction of the invaders. These include:

• Increased blow flow to the area to maximise the number of leukocytes that can get to the infection site.
• A thinning of the cells in local blood capillary walls (endothelial cells) to allow the leukocytes to squeeze through.
• An increase in local temperature which has an antibiotic effect.
• A large number of immune system signalling molecules (chemokines) are released by leukocytes to co-ordinate the immune response and to call more leukocytes to the site.

In a skin infection, all these changes cause the hot, swollen and painful symptoms that we are all familiar with. The pus that often results is the debris of dead bacteria, leukocytes and other cells.

Once the invader has been dealt with, the body terminates the immune response by killing off the leukocytes in the locality. This is done by depriving them of nutrients (necrosis) and by making them commit suicide (apoptosis). There are two ways that apoptosis happens:

1. by sending cells special cellular messenger molecules (cytokines) to tell them to die.
2. By not sending them other cytokines that tell them to keep living. A type of leukocyte, a helper T-cell, continues to release this type of cytokine while it continues to detect the presence of the pathogen. Once it can no longer detect it, it stops and other leukocytes die.

In multiple sclerosis and other autoimmune diseases, the inflammatory response seems to be launched in the absence of a pathogen. It seems that certain T-cells are mistakenly recognising the insulating sheaths around nerves (myelin) as a foreign invader.

Inflammatory Response links:
The Inflammatory Response

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MS Glossary
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