I've been reading a lot lately about the immune system and how
overreactions to particles such as pollen & dust mites result in
allergy symptoms. But what I can't find information on is how such
particles are dealt with in non-allergic individuals. When one who is
non-allergic breathes in pollen & dust-mites, don't these particles
have to be cleared out of the lungs somehow? If so how does this
occur? Do phagocytes just quietly engulf the particles without
triggering inflammation? What is the process?

Thanks for any help,
James

bryan heit

The difference is quite profound. The first thing worth mentioning is
that "normal" people still have immune responses to allergens, but the
nature of the response is very, very different from those with allergies.

It all centers around antibodies - when you are first exposed to an
allergen your body will develop an immune response against it, and part
of this response is the production of antibodies against that allergen.
These antibodies then circulate through your body for the rest of your
life (or at least a large portion of it), and mediate future immune
responses against that allergen.

Not all antibodies are the same - in fact there are several major
"flavors" (called isotypes) of antibodies, and these isotypes have
specific roles in the immune system. "Normal" people will produce the
IgG isotype of antibody in response to an allergen. This type of
antibody will bind to the allergen and then allow cells like macrophage
to bind to the antibody/allergen complex. These immune cells can then
take up (i.e. "eat") the allergen and destroy it.

People who develop allergies to an allergen produce a different isoform
of antibody, called IgE. IgE also binds to the allergen, but instead of
targeting the allergen to macrophage for degradation, these antibodies
direct the allergen to other immune cells - mast cells and eosinophils.
These cells are specialized cells which are usually used to kill
large pathogens (i.e. hook worms, liver flukes, and the like). Because
these cells are targeted against pathogens too big for the cells to
"eat", these cells instead release a lot of toxic stuff when they bind
to IgE, instead of engulfing and destroying he antigen.

Many of the chemicals released by these cells have systemic effects -
substances like histamine and leukotrienes have profound effects on
breathing, blood pressure, and also induce inflammation of the
surrounding tissue. It is these chemicals which induce the allergic
response. In some cases these substances can induce responses so strong
that it kills the patient.

Bryan

<snip>

Bryan, thanks so much for the detailed response. Exactly what I was
looking for.

Regards,
James