20. Hypersensitivity Reactions - Type II and III

Question 1

What are the mechanisms by which antibodies and complement can destroy cells in type II hypersensitivity?

Answer 1

1. Cell lysis if Complement cascade is completed through C9
2. Opsonization and phagocytosis of cell
3. ADCC = Ab- dependent cellular cytotoxicity

Question 2

What type of hypersensitivity reaction is involved in the following conditions: hemolytic disease of the newborn; autoimmune hemolytic anemia; Grave’s disease?

Answer 2

Autoimmune hemolytic anemia = cell destruction by Type II hypersensitivity.
Graves disease = cell stimulation by Type II hypersensitivity

Question 3

How does complement cause pathology in type III hypersensitivity?

Answer 3

Complement components have biologic activities:
C3a, C5a = Anaphylatoxin activitiy (vasodilation/vasopermeability)
C5a = chemotactic activity
C3b = opsonization

Question 4

What type of hypersensitivity reaction is involved in the following conditions: Arthus reaction; serum sickness; SLE?

Answer 4

Arthus reaction = local reaction caused by Type III hypersensitivity
Serum sickness and SLE = systemic reactions caused by Type III hypersensitivity

Question 5

In an SLE patient experiencing severe disease manifestations, would you expect the level of serum complement to be increased, decreased, or the same, as compared to that of a healthy individual? what about total serum Ig levels or specific Abs? Immune complexes?

Answer 5

Serum complement = Decreased, because they are being used and complexed

Total serum Ig, Specific Abs, and Immune complex assays = Elevated