Download Immune System Disorders

Immune System Disorders
Occasionally the reactions of the immune system are harmful:
Instead of producing a desirable result, such
as immunity to disease, the immune
system may over-react, react to the wrong
substances, or not react when it should.
The immune system may fail to detect
an infectious agent that has penetrated the
first and second lines of defense.
Some immune system disorders cause only
Photo: CDC
discomfort, as in the case of hayfever.
Immune system failure may lead to lifethreatening conditions, such as anaphylaxis,
AIDS and cancer (when the abnormal tumor
cells escape immune system detection).
Kaposi’s sarcoma in the foot area
of an immune supressed AIDS
patient
Autoimmune Diseases
Rheumatoid arthritis
Inflammation of joints
leading to destruction
of cartilage.
Some people have an
immune system that
fails to appropriately
recognize substances
Axon
from their own body
and attacks them.
Autoimmune diseases
are the result of the
damage caused by the
immune system
responding to self
antigens.
Myelin layer
Multiple sclerosis
A progressive inflammatory
disease causing paralysis.
Caused by the myelin layers
around nerve axons being
destroyed.
Hemolytic anemia
A disorder in which the red
blood cells rupture or are
destroyed at an excessive
rate. Caused by a variety of
factors including excessively
fragile red blood cells,
hereditary, and autoimmune
disorders.
Hypersensitivity
Hypersensitivity refers to an immune system
response to an antigen beyond what is
considered normal.
The immunological response to the antigen
(or allergen) leads to tissue damage rather
than immunity.
Photo: Eyewire
Hypersensitivity reactions occur when a
person has been sensitized to an antigen.
Allergic reactions (e.g. hayfever, asthma, and
anaphylaxis from insect venom or drug
injections) are rapid. They occur when
antibodies respond to an allergen by causing
the release of histamine from mast cells.
An SEM photo showing a pollen grain
Photo: EII
Allergies
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When the immune system responds to harmless
substances
Allergens – antigenic substances which do no real harm
Allergens include house dust, animal skin, pollen,
house dust mite and its faeces
Allergies
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Histamine causes blood vessels to widen and become
leaky.
Fluid and white blood cells leave capillaries.
The area of leakage becomes hot, red and inflamed
Allergies
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Allergic responses such as asthma are the result of a
vigorous overreaction of the immune system to a
previously encountered antigen.
Mast cells are immune cells involved in allergic
responses, they are non- motile, found around blood
vessels, in connective tissue and in the lungs. Mast
cells release active agents such as Histamine, which
cause contraction of smooth muscles & vasodilation
of blood vessels, leading to swelling and inflammation.
Treatment includes use of antihistamine drugs.
The Basis of Hypersensitivity
B cell encounters
the allergen and
differentiates into
numerous
plasma cells.
B cell
Plasma cell
The plasma cell
produces antibodies.
Mast cell
Vesicles with
histamine
Antibodies bind to specific
receptors on the surface
of the mast cells.
The mast cell binds the allergen when it
encounters it again. The mast cell releases
histamine and other chemicals, which together
cause the symptoms of an allergic reaction.
Hayfever
Hayfever (allergic rhinitis) is an allergic
reaction to airborne substances such as:
dust, moulds, pollens, and animal fur or
feathers.
Photo: EII
Allergy to wind-borne pollen is the most
common. Certain plants (e.g. ragweed
and privet) are highly allergenic.
An SEM photo showing a pollen grain
Photo: James H. Miller, USDA Forest Service, Forestryimages.org
There appears to be a genetic
susceptibility to hayfever, as it is
common in people with a family history
of eczema, hives, and/or asthma.
Those with hayfever are best to avoid
the allergen, although anti-histamines,
decongestants, and steroid nasal sprays
will assist in alleviating symptoms.
A privet plant in flower
Asthma
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Attacks can occur at any time
Genes play a role in who develops asthma
Breathing becomes difficult, sufferers experience
wheezing, coughing, a tightness about the chest and
shortage of breath.
1/7 children in UK has asthma, number is increasing.
>1000 people die each year from asthma every year in
the UK
Asthma
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Airways in asthmatics are always inflamed, during an
attack this worsens.
Fluid leaks from blood into airways and goblet cells
secrete lots of mucus
Airways can become blocked
Muscles surrounding trachea and bronchioles contract
which narrows airways further
Asthma
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Vaccines are being developed to make allergic
responses less severe
Designed to desensitise people so they do not produce
antibodies to allergens
Genetic tests may be used to screen children and then
a vaccine could be given to prevent them developing
asthma
Blood group
Antigens present on the red blood cells
A
antigen A
B
AB
O
antigen B
antigens
A and B
Neither
antigen
A nor B
Antibodies present in the plasma
Contains anti-B antibodies,
but no antibodies that would
attack its own antigen A
Contains anti-A antibodies,
but no antibodies that would
attack its own antigen B
Contains neither anti-A
or anti-B antibodies
Contains both anti-A
and anti-B antibodies