10 February 2009

How mast cells work

Your body is a weapon. The immune system is a machine of war, ready to take on invaders. The immune system has its own internal affairs department: it can identify cells which are

Your body is a weapon. The immune system is a machine of war, ready to take on invaders. The immune system has its own internal affairs department: it can identify cells which are infected with viruses and which are in the process of becoming tumours.

But like all armed forces, your immune system makes mistakes. In real life they call it friendly fire, an oxymoron like negative growth or military intelligence. In your body it’s called an allergic reaction.

In its allergic mode, your immune system misidentifies an otherwise benign substance as harmful, and then attacks the substance with a vigour and ferocity that’s far greater than required.

This can cause you to feel either mildly inconvenienced, or it can lead to the complete failure of the organism the immune system is supposed to protect.

Mast cells play a vital role in allergies because they produce histamine, a key weapon in the body’s flight against infection.

The problem is that when histamine is released in too great a quantity or at the wrong time it creates trouble.

It takes around eight days for the mast cells to become primed with IgE antibodies, the antibodies that react to intrusion.

After that, if the allergen is encountered, it triggers a destructive domino effect within the immune system known as an allergic cascade. So whether it’s a pollen particle that’s been inhaled or venom of a honeybee that’s been injected into your bloodstream, it results in the same sequence of events.

Here’s what happens next:

  • IgE antibodies on the surface of mast cells recognize the allergen. They actually identify it by its protein;
  • The IgE antibodies attach themselves to the protein (the proper name is protein surface markers), while staying attached to the mast cells;
  • The binding process sends an alert to a group of special proteins called the complement complex that circulate in your bloodstream;
  • After the IgE antibody, which is attached to a mast cell, binds to an allergen, the first complement protein attaches itself to the site. This alerts the next protein in the sequence, which in turn alerts the next one, and so on. When this process is completed, the allergenic cell is destroyed;
  • In a healthy immune system this is fine. But in when the body has misidentified the cell it triggers what’s called allergic episode. When this happens, the cells involved are mast cells;
  • When mast cells are destroyed, their stores of histamine are released into the surrounding tissue and bloodstream. This triggers a dilation of surface blood vessels and a drop in blood pressure. The spaces between the surrounding cells then fill with fluid.

Depending on the part of the body or the allergen involved, this heralds the onset of various allergy symptoms, some of the most common being:

  • Itching of the body, eyes and nose;
  • Hives;
  • Sneezing;
  • Wheezing;
  • Nausea;
  • Diarrhoea;
  • Vomiting.

Allergy Society of South Africa (ALLSA)


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