Hypersensitivity

Question 1

What 3 types of antigens can trigger hypersensitivity possibly leading to chronic diseases?

Answer 1

1. Self-antigen
2. Microbial antigen
3. Environmental antigen

Question 2

What is Type I Hypersensitivity also known as?

Answer 2

Immediate, IgE-mediated, allergy/atopy Hypersensitivity

Question 3

Describe Type I Hypersensitivity

Answer 3

1. Timing: within seconds to minutes
2. Involves antigen-specific IgE on effector cells
3. Vasoactive (Histamine) & eicosanoids and cytokines are released

*Most common type of hypersensitivity

Question 4

Allergic rhinitis (hay fever), atopic asthma, anaphylaxis are examples of

Answer 4

Type I Hypersensitivity

Question 5

Which types of Hypersensitivity are mediated by antibodies?

Answer 5

Type I, II, and III

Question 6

Which type of hypersensitivity is local, tissue/cell specific?

Answer 6

Type II

Question 7

Which type of hypersensitivity is general/systemic and related to immune complex deposition?

Answer 7

Type III

Question 8

Which immunoglobulins have subtypes/subclasses?

Answer 8

IgA (2) & IgG (4)

Question 9

Which immunoglobulin has the highest concentration and the longest half-life in the serum?

Answer 9

IgG

Question 10

Which immunoglobulins have different forms?

Answer 10

IgA (monomer, dimer) & IgM (monomer, pentamer)

Question 11

What is Type II Hypersensitivity also known as?

Answer 11

Antibody-mediated, cytotoxic

Question 12

Describe Type II Hypersensitivity

Answer 12

1. Timing: within minutes to hours
2. Involves IgM and IgG
3. 3 mechanisms

Question 13

What is the complement and Fc receptor mediated mechanism of Type II Hypersensitivity?

Answer 13

Antibodies bind to antigens (allow direct binding of phagocytes on Fc portion) or activate complement (through classical pathway) which leads to inflammation (attract neutrophils).

Ex. Goodpasture Syndrome

Question 14

Describe Goodpasture Syndrome

Answer 14

aka. anti-glomerular basement membrane disease

Antibodies are produced against basement membrane in kidney and lung.

Symptoms: bloody urine/lung, kidney failure

Question 15

What is the opsonization and phagocytosis mechanism of Type II Hypersensitivity?

Answer 15

Antibodies opsonize the outside of cells and then phagocytes come and eat them up.

Ex. Idiopathic Thrombocytopenic Purpura (No platelets)
Ex. Autoimmune Hemolytic Anemia (AIHA)

Question 16

Describe ITP

Answer 16

Auto-antibodies are produced against platelets. Platelets are opsonized and removed in the spleen.

Symptoms: easy/persistent nose bleeding

Question 17

Describe AIHA

Answer 17

Auto-antibodies are produced against RBC membrane proteins.

Symptoms: faigue, jaundice, pallor (pale skin), weakness

Question 18

What is the abnormal physiologic responses without cell/tissue injury mechanism of Type II Hypersensitivity?

Answer 18

1. Graves’ Disease: Antibody binds TSH receptor (turns it on) without the presence of hormone/ligand. Causes hyperthyroidism.
2. Myasthenia Gravis: Antibody binds ACh receptor and prevents ACh hormone from binding and signaling muscle contraction.

Question 19

Acute rheumatic fever (myocardial antigens), pemphigus vulgaris (desmosomes), and pernicious anemia (intrinsic factors) are examples of

Answer 19

Type II Hypersensitivity

Question 20

What is Type III Hypersensitivity also known as?

Answer 20

Immune Complex mediated

Question 21

Describe Type III Hypersensitivity

Answer 21

1. Timing: within hours
2. Involves IgM and IgG
3. Due to accumulations of immune complexes in vessels, joints causing complement/Fc receptor inflammation leading to attraction of neutrophils/macrophages (vasculitis).

Ex. Serum Sickness
Ex. Systemic Lupus Erythematosus (SLE)

Question 22

What is an immune complex?

Answer 22

an antigen-antibody complex

Question 23

What is serum sickness?

Answer 23

A phenomenon when patient makes antibodies against the foreign horse antibodies (against diphtheria) causing complex formation and deposition.

Question 24

Describe SLE

Answer 24

SLE has type II hypersensitivity with blood (low WBC, RBC, and platelets), but majority of lupus symptoms are classic type III.

Symptoms: Malar rash (butterfly), fever, joint pain

Question 25

Poststreptococcal glomerulonephritis (group A strep antigen) and polyarteritis nodosa (HBV surface antigen) are examples of

Answer 25

Type III hypersensitivity

Question 26

What is Type IV Hypersensitivity also known as?

Answer 26

Delayed Type, cell-mediate

Question 27

Describe Type III Hypersensitivity

Answer 27

1. Timing: Days (slowest)
2. Involves T cells (CD4 or CD8)–> 2 mechanisms
3. Not transferrable by serum like in case of antibodies

Question 28

What is cytokine-mediated inflammation mechanism of Type IV Hypersensitivity?

Answer 28

APC presenting tissue antigen is recognized and bound by CD4 T cell. IFN-y is released and causes inflammation (attraction of macrophages, neutrophils) and tissue injury.

Ex. TST

Question 29

What is another name for TST or PPD test for tuberculosis?

Answer 29

Mantoux Test

Question 30

What is T cell mediated killing of host cells mechanism of Type IV Hypersensitivity?

Answer 30

Host cell infected with antigen presents MHC I + peptide and is recognized by CD8 for direct killing leading to cell death/tissue injury.

Ex. Contact Dermatitis (poison ivy)

Question 31

Describe Poison Ivy contact dermatitis

Answer 31

The antigen, urushiol (colorless oil) is lipid soluble so crosses cell membrane and gets presented by cells (MHC I). CTL recognizes, binds, and triggers cell destruction/apoptosis.