In my last post, which was about how and why the cells
within our bodies communicate amongst each other, I used the example of our
immune system. This incredible network of white blood cells guards our bodies
against disease-causing microorganisms with a variety of defensive mechanisms;
the importance of our immune system is reflected in the disastrous consequences
of deficiency diseases such as AIDS. Without an immune system, a common cold
would kill you. The whole system relies on the fact that our white blood cells
recognise pathogens as foreign, and thus set off an alarm signal which triggers
the whole response – including the familiar symptoms of coughing, fevers and
inflammation. As amazing as it is, the immune system is not infallible, and
often can be set off by harmless substances which happen to find their way into
our bodies – resulting in an allergic reaction.
When an allergen enters your body (which may be from eating
it, breathing it in, or via the bloodstream, e.g. insect bites), it will bind
to specific receptors on white blood cells – this happens because of their
complementary shape. These cells will then send out signals which trigger the production
of a type of antibody called Immunoglobulin E, or IgE1. IgE then
goes and attaches to another type of white blood cell called mast cells2.
The next time that allergen comes along, it will bind to the IgE antibodies,
which once again have a specific shape which allows them to recognise the
invading substance3. The
binding of the allergen causes IgE to change shape, kicking into an action a signal transduction pathway which causes
the mast cells to release chemicals such as histamine4.
The effect of these chemicals is to induce the well-known
allergy symptoms: in nasal allergies (collectively known as allergic rhinitis5),
such as hay fever, histamine causes inflammation, sneezing, running nose, etc.
but some allergic reactions have more serious effects. Anaphylaxis, for
example, can be brought on by an allergy to nuts or insect venom; characterised
by symptoms such as rapid swelling and hives, anaphylaxis can be fatal if not
treated6.
So essentially, your immune system does a great job of
protecting you from nasty bacteria, viruses and fungi, but every so often it
gets it wrong, going into overdrive at the first sign of something harmless
like pollen or pet hair. In a sense, it’s the price that must be paid for
having a really good immune system; so while hay fever can be a real nuisance
and many allergies can be very harmful, it’s a lot better than not having a
working immune system at all!
References
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