16. Hypersensitivity Reactions (III & IV)

Question 1

What causes Type III Hs?

Answer 1

large amounts of immune complexes that aren’t removed by normal mechanism

Question 2

What are some examples of Type III Hypersensitivity disease?

Answer 2

Serum sickness, Farmer’s lung caused by inhalation of moldy hay

Question 3

What are the hallmarks of DTH (Type IV)?

Answer 3

• Delayed time for reaction to develop
  o 1-3 days
• Purely cell-mediated rather than Ab mediated
• Recruitment of Macs (as opposed to neutrophils in type III reactions)

Question 4

Basics of Type IV DTH

Answer 4

T helper cells encounter Ag, secrete cytokines that induce localized inflammatory reaction (delayed type hs), cytokines cause large influx of Macs which cause tissue damage

Question 5

Immune complex =

Answer 5

Ab plus soluble Ag

Question 6

Immune complexes can damage tissue. T or F?

Answer 6

TRUE

Question 7

What type of response occurs if immune complex is deposited near site of Ag entry?

Answer 7

localized reaction

Question 8

(Type III) What type of response occurs if complexes are formed in the blood?

Answer 8

reactions develop where deposited

Question 9

(Type III) After immune complex is formed, what four steps occur:

Answer 9

1. Immune complex activates complement
2. Generation ofo anaphylatoxins (C3a, C4a, C5a)
3. Recruit neutrophils and granule release
4. Anaphylatoxins cause mast cell degranulation

Question 10

Deposition of immune complexes can trigger

Answer 10

release of inflammatory mediators and vasoactive mediators including proteases which may damage connective tissues; clots may form as complexes activate platelets

Question 11

Deposition of immune complexes in blood vessels causes

Answer 11

vasculitis

Question 12

Deposition of immune complexes in kidneys causes

Answer 12

glomerulonephritis

Question 13

Deposition of immune complexes in joints causes

Answer 13

arthritis

Question 14

Arthus reactions are

Answer 14

localized Type III Hs reactions

Question 15

Why is granuloma a double edged sword?

Answer 15

walls off organism in the infected tissue; macrophage lytic enzymes damage the body tissue

Question 16

Explain skin testing for DTH reactions.

Answer 16

• To determine whether a person has been exposed to M. tuberculosis:
• PPD (bacterial cell wall protein) is injected intradermally
• Development of firm, red, swollen lesion @ 48-72 h indicates previous exposure
• Positive result indicates person has population of sensitized Th1 cells

Question 17

Skin test for DTH reaction distinguishes whether exposure was to pathogenic for or to vaccination. T or F?

Answer 17

FALSE; skin test does not distinguish between exposure to pathogen for or to vaccination

Question 18

Contact dermatitis is a Type IV Hs. T or F?

Answer 18

TRUE

Question 19

How can sensitization occur?

Answer 19

if a reactive chemical compound binds to skin proteins

Question 20

Type IV Hs can be induced by:

Answer 20

pharmaceuticals, cosmetics, industrial chemicals, metal ions, and more

Question 21

What type of Hs can cause strong cell-mediated responses against skin cells, inducing blister-like lesions and rashes?

Answer 21

Type IV Hs (DTH)

Question 22

Tolerance =

Answer 22

prevention of an immune response against self Ags

Question 23

Central tolerance is the prevention of an immune response against self Ags by what mechanism?

Answer 23

deletion of lymphocytes before they mature; central tolerance limits development of autoreactive T and B cells

Question 24

Where does tolerance occur?

Answer 24

generative lymphoid organs

Question 25

Peripheral tolerance =

Answer 25

either renders self-reactive lymphocytes nonresponsive or actively generates inhibitive lymphocytes outside the bone marrow and thymus

Question 26

Antigen sequestration

Answer 26

a means to protect self antigens from attack

Question 27

What are some examples of antigen sequestration?

Answer 27

-anterior chamber and lens of eye lack lymphatic drainage -blood brain barrier -development of male reproductive cells

Question 28

What does peripheral tolerance regulate?

Answer 28

autoreactive cells that made it into circulation

Question 29

Name the 3 steps of peripheral tolerance.

Answer 29

1. if T cells only receive "signal 1" they become anergic 2. CTLA-4 expression on T cells (in lieu of CD28) 3. Induction of T regulatory cells

Question 30

T regulatory cells are

Answer 30

regulatory CD4+ T cells which can be generated in they thymus or in the periphery following Ag induction

Question 31

Treg cells still engage Ag-MHC Class II complexes through TCR. T or F?

Answer 31

TRUE; but they downregulate responses when they do so

Question 32

Name four mechanisms by which Tregs suppress.

Answer 32

1. kill APCs and effector T cells by perforin and granzymes 2. inhibit APC function via CTLA-4 3. secrete immune inhibiting cytokines such as IL-10 and TGF-beta 4. act like a sponge to absorb IL-2 so other T cells can't get fully

Question 33

Autoimmunity =

Answer 33

when the immune system turns on itself due to a lack of self tolerance

Question 34

Some autoimmune diseases are mediated by direct cellular damage. Explain this four step process.

Answer 34

1. lymphocytes or Abs bind to cell-membrane self Ags 2. cellular lysis and/or inflammatory response 3. damaged tissue replaced by scar tissue 4. organ function declines

Question 35

Hashimoto's thyroiditis is most common in what population?

Answer 35

middle aged women

Question 36

Hashimoto's thyroiditis decreases the function of what?

Answer 36

thyroid function, leading to hypothyroidism

Question 37

Explain the role of Ab in Hashimoto's thyroiditis.

Answer 37

Auto Abs and Th1 cells produced are specific for thyroid Ags; Ab produced interferes with iodine uptake

Question 38

Diseases characterized by induced DTH response in the thyroid.

Answer 38

Hashimoto's Thyroiditis

Question 39

Goiter

Answer 39

visual enlargement of the thyroid gland as a result of inflammation induced by DTH response in thyroid (intense WBC infiltration)

Question 40

CTLA-4 expression only occurs on what type of cells?

Answer 40

activated T cells

Question 41

CTLA-4 binding to _________________ inhibits T cells.

Answer 41

CD80/86

Question 42

Mice lacking CTLA-4 show widespread _________________ disease.

Answer 42

autoimmune