Type III and IV Hypersensitivity Reaction Flashcards Preview

PoD Test 1 > Type III and IV Hypersensitivity Reaction > Flashcards

Flashcards in Type III and IV Hypersensitivity Reaction Deck (22)
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1
Q

What is a type III hypersensitivity reaction?

A

Soluble antigen and specific antibody form a complex depositing in blood vessel membrane and causing tissue damage by inflammation (vasculitis)

Clinical: >3-6 hours after antigen exposure

2
Q

How is a type II reaction generated?

A

Antibody binds to an antigen as a soluble complex and deposits in small blood vessel.

C3b binds to exposed Fc site and complement activation/neutrophilic inflammation in vessel occurs

3
Q

What is serum sickness?

A

Type III reaction against foreign antigens (e.g. antivenom)

4
Q

How is vasculitis induced in a type III reaction?

A

Immune complex deposition leads to platelet aggregation and microthrombus formation

Immune complexes/complement products from activated cascade act on complement receptor on basophil/mast cell to allow for release of vasoactive amines

5
Q

How do you differentiate a “hive” from type I reactions and type III reactions?

A

Type I - presence of itching

Type III - presence of vessel damage indicates source is non-allergic

6
Q

What is Rheumatoid Arthritis?

A

Type III hypersensitivity reaction

Rheumatoid factor is patient’s autoantibody of IfM Fab component directed against Fc portion of own IgG

7
Q

What is the therapy for rheumatoid arthritis?

A

Anti-cytokine monoclonal antibody

Anti-B cell monoclonal antibody

8
Q

What is the antibody isotype of immune complex of Henoch Schonlein Purpura?

A

IgA

9
Q

What is post-streptococcal glomerulonephritis?

A

Type III hypersensitivity reaction

Causes immune complex deposition in the capillary/kidney unit (glomerulus)

10
Q

What is the arthus reaction?

A

Local immune complex deposition after antigen injection in skin with preformed antibody present

Occurs in presensitized individuals

Edema, necrosis, complement activation

11
Q

How can you test for type III hypersensitivity?

A

Skin or renal biopsy - leukocytoclastic vasculitis with infiltrate of neutrophils (lumpy bumpy appearance)

Hypocomplementemia - complement activation depletes C3/C4

Small vessel vasculitis in favored locations of kidney, joint, skin

12
Q

What is the therapy for type III hypersensitivity reactions?

A

Glucocorticoids and plasmapheresis (acute flare)

Immunosuppressants fro autoimmune disease

13
Q

What is a type IV hypersensitivity reaction?

A

Inflammation via CD4 T cell cytokine activation of macrophages and /or CD8 T cell mediated cell lysis

> 48 hours to weeks develop

14
Q

What is Steven’s Johnson Syndrome/Toxic Epidermal Necrolysis?

A

Type IV hypersensitivity reaction caused by drugs such as penicillin, sulfa or anti-seizure

Also caused by infection such as HSV or Mycoplasma

15
Q

What is the mechanism of SJS/TEN?

A

CD8 T cell response to drug hapten or antigen causes T cell activation which kills keratinocytes via cytolysis

Also induces apoptosis

16
Q

What is the therapy for SJS/TEN?

A

Cyclosporine, glucocorticoids

17
Q

What is the mechanism of Allergic Contact Dermatitis?

A

Antigens are soluble haptens which bind to keratinocytes enabling immunorecognition

Memory T cells (4 and 8) in dermis proliferate on 2nd exposure and inflammatory infiltrate ensues

18
Q

What is the therapy for allergic contact dermatitis?

A

Antigen removal and glucocorticosteroids

19
Q

How do you test for type IV hypersensitivity?

A

Sensitizing agent placed on skin and then examined in 48 hours

20
Q

What antigen properties enable type IV reaction?

A

Environmental chemical antigens

Hard to clear, chronic intracellular pathogens

Medication (haptens, e.g. penicillin and sulfa drugs)

Self antigens - MS, insulin dependent diabetes, RA

21
Q

What infection is a source of delayed type IV reaction?

A

TB

22
Q

What does the PPD (Mantoux test) reflect?

A

Reflects INF-gamma production by antigen specific CD4 T cells

Immunosuppression will decreasee the size of the reaction