Microbiology Chapter 16
Chapter 16 Immune System Disorders
The 3rd line of defense – The immune response is fantastic
and helps us survive in a world populated by harmful
agents – but sometimes things go wrong and our
own immune system causes us problems. Hay fever
and food allergy are not uncommon. Severe disorders
can be serious to fatal.
Hypersensitivity – body responds to allergen – immunological
response – but tissue damage instead of immunity is the
result.
Microbiology Chapter 16
1. Allergen - antigen that causes a hypersensitivity
reaction
2. Sensitized – person is exposed to this allergen
3. Hypersensitivity reaction – re-exposed to allergen
– resulting in harmful reaction
4. 4 types of reactions
Fig. 16.1
Microbiology Chapter 16
Microbiology Chapter 16
Type 1 Hypersensitivity – Anaphylaxis (Pg. ___)
1. Occurs quickly 2 – 30 minutes
2. Involves IgE antibodies
3. Can be localized hypersensitivity or generalized
a. Localized common allergic reaction like hay
fever, food allergies
b. Generalized – affect breathing, drop in blood
pressure
4. Sensitizing results in production of IgE antibodies,
2nd exposure causes
IgE ab bind with surface of mast cells (in
tissues) and basophils (blood)
Microbiology Chapter 16
a. Symptoms are related to these cells
degranulating and dumping of chemical
mediators like histamine
b. Histamine, most well known, causes
vasodilation, edema, swelling, redness
(common hay fever)
c. Other mediators can cause the symptoms of
asthma
d. Systemic anaphylaxis – injected allergens in
particular, drop in blood pressure (shock) can
be fatal in minutes – insect stings, penicillin
(hapten)
Fig. 16.3
Fig. 16.4
Microbiology Chapter 16
Type 2 Hypersensitivity – Cytotoxic reaction, IgM and IgG, these
with cells, and with complement cause cells to lyse
1. Common transfusion reactions – pg.495 abo blood grouping
2. In transfusion reactions, ag-ab complex and complement in se
donors rbc to lyse
3. Rh factor is also a cytotoxic reaction – Rh+ and Rh-, negative
exposed to positive develops ab to rh ag, 2nd expsoure can resu
cytotoxic reaction
Microbiology Chapter 16
Type 2 Hypersensitivity – Cytotoxic reaction, IgM and IgG,
these antibodies react
with cells, and with complement cause cells to lyse
1. Common transfusion reactions – pg.___ abo blood
grouping
2. In transfusion reactions, ag-ab complex and complement in
serum cause donors rbc to lyse
3. Rh factor is also a cytotoxic reaction – Rh+ and Rh-,
negative when exposed to positive develops ab to rh
ag, 2nd expsoure can result in cytotoxic reaction
Fig. 16.9
Microbiology Chapter 16
a. Erythroblastocysis fetalis – hemolytic disease of the
newborn
b. Prevented now with rhogam – preformed antiRh antibody
(passive immunity) prevents mom from developing
own antibodies if exposed to Rh antigen at time of birth
(P._____)
c. Total transfusion was used before
Fig. 16.10
Fig. 16.11
Fig.
16.12
Microbiology Chapter 16
Type 3 – Immune complex hypersensitivity – antibodies
against soluble antigens in the serum (pg.____)
1. IgG antibodies, the ab react with antigens in serum and
these complexes are deposited in the cells of
basement membrane tissue
2. The subsequent complement fixation results in severe
tissue damage
3. Glomerulonephritis kidney damage
4. Systemic type 3 reactions – auto allergies – lupus (sle),
rheumatoid arthritis (IgM and IgG complexes in tissue
of joints)
Fig. 16.13
Microbiology Chapter 16
Type 4 – Cell mediated hypersensitivity - t cells involved (td)
– delayed hypersensitivity – symptoms are slow, at
least a day or two
1. Time is required for the T cells and macrophages to
migrate to site of foreign antigens
2. Allergic contact dermatitis is an example (poison ivy) see
pg____
3. T cells are exposed to allergen, develop clone of t memory
cells, these are circulating and are ready to interact
with later exposure to antigen
4. Tb skin test uses this type of reaction to detect earlier
exposure to tb ag
5. Inflammation reaction – macrophages dump (degranulate),
(histamine reaction in tissue) redness, swelling, itch
Fig. 16.15
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Microbiology Chapter 16
Autoimmune diseases – self antigens cause improper
immune response, a break down in self tolerance (pg.____)
1. Body produces ab to own ag
2. Sensitized t cells react against the body’s own tissue
antigens
Transplants – foreign tissue can be perceived as antigenic, a
tissue can then be rejected as T cells and antibodies attack
the foreign tissue – need immunosuppresant drugs
Microbiology Chapter 16
1. Congenital – borne with defective immune
system
2. Acquired – drugs, cancers, virus cause the
degradation of immune system
3. HIV virus and aids – we’ll cover it later in
disease of blood and emerging
diseases
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Microbiology Chapter 16