Classify the hypersensitivity reactions, give an example for each reaction and describe the pathophysiological processes of each reaction.
A tabular format is a very desirable format for a response to this question. Again candidates
who struggled to provide an organised response also failed to provide sufficient and succinct
detail in their answer. A good answer would have included the following features.
| Mechanism | Pathophysiology | Disease types |
|
Type I |
· basophil & mast cell degranulation · histamine, SRSA, ECFA, NCF · immediate weal & flare |
· anaphylaxis |
|
Type II |
· direct phagocytosis or cell lysis · activation of complement, classical · tissue deposition of complement |
· blood transfusions |
|
Type III |
· tissue deposition of Ag-Ab complexes · accumulation of PMN's, macrophages & complement |
· SLE |
|
Type IV |
· T-cell induced mononuclear cell accumulation · release of lymphokines & monokines · often with granuloma formation |
· TB, sarcoid |