microbiology chapter 16

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

Microbiology Chapter 16Fig. 16.1

Microbiology Chapter 16

Type 1 Hypersensitivity – Anaphylaxis (Pg. ___)1. Occurs quickly 2 – 30 minutes2. Involves IgE antibodies3. Can be localized hypersensitivity or generalized

a. Localized common allergic reaction like hay fever, food allergiesb. Generalized – affect breathing, drop in blood pressure

4. Sensitizing results in production of IgE antibodies, 2nd exposure causesIgE 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 antibodies reactwith cells, and with complement cause cells to lyse1. Common transfusion reactions – pg.495 abo blood grouping2. In transfusion reactions, ag-ab complex and complement in serum causedonors rbc to lyse3. Rh factor is also a cytotoxic reaction – Rh+ and Rh-, negative whenexposed to positive develops ab to rh ag, 2nd expsoure can result incytotoxic 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 two1. Time is required for the T cells and macrophages to migrate to site of foreign antigens2. 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 antigen4. Tb skin test uses this type of reaction to detect earlier exposure to tb ag5. 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 ag2. 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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