14 Hypersensitivity and Autoimmunity I

Question 1

What are the two ways in which the immune system can go wrong?

Answer 1

exaggerated responses (hypersensitivity) and autoimmune responses

Question 2

what are the four mechanisms of immunopathology?

Answer 2

Type I. Anaphylactic/atopic
Type II. Cytotoxic injury
Type III. Immune-complex mechanism
Type IV. Delayed hypersensitivity

Question 3

What is the mechanism of Type I hypersensitivity?

Answer 3

First, IgE binding to mast cells and basophils results in release of histamine, which causes vasodilation and leakage, an increase in mucus, eosinophil infiltration, and vascular collapse. Later, synthesis and release of prostaglandins and leukotrienes results in prolongation of symptoms.

Question 4

T/F: Type II hypersensitivity may involve either cytotoxic or noncytotoxic mechanisms.

Answer 4

T

Question 5

How does cell death occur in Type II cytotoxic hypersensitivity?

Answer 5

The target cells are opsonized by antibodies, and undergoes various cytotoxic processes, such as attack by killer T-cells and myeloid cells, complement mediated lysis, and immune adherence to and destruction by phagocytes of spleen

Question 6

T/F: hemolysis of donor RBCs of an incompatible blood type is an example of type III hypersensitivity.

Answer 6

F; type II

Question 7

What are non-cytotoxic type II reactions?

Answer 7

antibodies to structural proteins (eg Pemphigous and pemphigoid diseases)

Question 8

review slide 12 for examples of immunohistochemistry staining of blistering diseases.

Answer 8

.

Question 9

antibodies to cell receptors in Type II reactions can activate or deactivate a cellular function. Name an example for each.

Answer 9

Thyrotoxicosis (Graves disease): Ab activates TSH receptor

Myasthenia gravis - Ab inactivates ACh receptors

Question 10

what are the symptoms of Graves disease?

Answer 10

heat intolerance, weight loss, hyperreflexia, and exopthalmia/proptosis

Question 11

what are the symptoms of myasthenia gravis?

Answer 11

muscle weakness

Question 12

What is the mechanism of Type III hypersensitivity?

Answer 12

1) Antibodies form against foreign or self antigens in the circulation
2) Complement activation leads to increased vascular permeability and increased activity of PMNS. Increased PMN activity leads to greater tissue infiltrate and phagocytosis and local destruction of blood vessels and connective tissue.

Question 13

What are the signs and symptoms of systemic immune complex diseases?

Answer 13

fever, urticaria, arthralgias, proteinuria and hematuria, lymphadenopathy

Question 14

T/F: hypersensitivity reactions are all mediated by antibodies.

Answer 14

F; I-III are, but IV is t cell mediated

Question 15

what are the two types of Type IV hypersensitivity reactions?

Answer 15

delayed hypersensitivity and cell-mediated cytotoxicity

Question 16

What is the mechanism of a type IV delayed hypersensitivity reaction?

Answer 16

Sensitized T lymphocytes direct the reaction, but recruit additional cells (especially macrophages) to act as major effector cells.

Question 17

What type of cells mediate type IV cell-mediated cytotoxicity reactions?

Answer 17

CD8 t cells

Question 18

TB skin test reaction is an example of what?

Answer 18

delayed hypersensitivity

Question 19

what is the time course of a delayed hypersensitivity reaction?

Answer 19

local erythema and induration appear after 8-12 hours. Reaction peaks after 2-7 days and slowly subsides.

Question 20

what is the time course of a granulomatous reaction?

Answer 20

Require weeks to months to develop and may resolve slowly or persist indefinitely.

Question 21

Transplant rejection is most like what type of hypersensitivity reaction?

Answer 21

Type IV

Question 22

T/F: in Graft vs. Host disease, the host attacks a transplanted tissue.

Answer 22

F; that is the definition of rejection. In GvHD, the graft immune cells attack the host

Question 23

Acute rejection is what type of hypersensitivity reaction?

Answer 23

Type IV

Question 24

Hyper acute rejection is what type of hypersensitivity reaction?

Answer 24

Type II

Question 25

What is hyper acute rejection?

Answer 25

occurs when host Abs attack vascular endothelium, resulting in antigen-Ab complexes and destruction of the vessels

Question 26

what is is called when anti-donor antibodies cause necrotizing vasculitis?

Answer 26

Acute humoral rejection

Question 27

What is goodpastures?

Answer 27

a condition in which patients make antibodies to type IV collagen in the lungs and kidneys, resulting in glomerulonephritis and pulmonary hemorrhages

Question 28

what type of hypersensitivity reaction is goodpastures?

Answer 28

Type II

Question 29

what type of hypersensitivity reaction is serum sickness?

Answer 29

Type III

Question 30

what are the symptoms of serum sickness?

Answer 30

high fever, rash, joint pain, and lymphadenopathy

Question 31

what causes serum sickness?

Answer 31

usually presents 1 wk after innoculation with anti-venom or drug treatment (eg streptokinase)