As
we have seen, an allergic reaction starts with an allergy
trigger being recognised by the body. However, this is just
the start of a process that involves a complex interplay
between dozens of chemicals that the body releases and several
categories of immune cells.
Mast cells
A good starting point in understanding the process that leads
to allergy symptoms is the mast cell.
Mast cells are filled with chemicals that cause inflammation,
the name itself comes from the German word mast meaning
fattening.
On the surface of each mast cell are thousands of receptors
that bind with the antibody involved in allergy. During an
encounter with an allergy trigger (allergen) the trigger
is recognised by these antibodies. Trigger and antibody bind
together. When an allergy trigger binds to two neighbouring
antibodies this causes the wall of the mast cell physically
to wiggle or judder. The cell breaks open, releasing an array
of chemicals that initiate the allergic reaction.
Mast cells contain 30 or more different allergy-causing
chemicals. The best known of these is histamine.
In airborne allergy histamine causes typical symptoms such
as sneezing,
a runny nose and itching of the nose and throat. However,
some of the other chemicals released by the mast cell are
just as disruptive as histamine. The complexity of the process
set underway by the release of chemicals from the mast cell
is one of the reasons why antihistamines alone
treat the early phase and not the late phase.
Early and late phase response
The initial allergic reaction produces symptoms within minutes.
It causes sneezing, a runny nose and itchy nose, and
throat. However, this early phase is just part of the process.
Many people also experience a late phase allergic reaction.
Mast cells initiate a slower, longer lasting reaction as
some of the released chemicals attract a variety of other
inflammatory cells to travel to the nasal passages. Here,
these cells produce swelling and blockage of the nasal passages.
The late phase response is also encouraged by the cells
responding to the impact of the early phase response.
The early and late phase allergic reactions together
create a bad allergic response.
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