Question

Given below are two statements, one is labelled as Assertion (A) and other one labelled as Reason (R).
Assertion (A) : Hemolytic disease after mismatched blood tranfusion is example of Type 2 hypersensitivity and may be sometimes with fatal outcome.
Reason (R) : Type 2 hypersensitivity is mediated by IgG and IgM directed against antigens on circulating red blood cells that leads to cell lysis
In light of the above statements, choose the correct answer from the options given below.

• A. Both (A) and (R) are true and (R) is the correct explanation of (A).
• B. Both (A) and (R) are true but (R) is NOT the correct explanation of (A).
• C. (A) is true but (R) is false.
• D. (A) is false but (R) is true.

Hint:

Remember the classic Coombs classification:
- Type I \(\rightarrow\) IgE-mediated (Allergy).
- Type II \(\rightarrow\) IgG/IgM against cell-surface antigens (Transfusion reaction, Rh disease).
- Type III \(\rightarrow\) Immune complexes (Serum sickness).
- Type IV \(\rightarrow\) T-cell mediated (Delayed type).

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
This question deals with immunology, specifically the classification and mechanisms of hypersensitivity reactions, with a focus on Type II (antibody-mediated) hypersensitivity.

Step 2: Detailed Explanation:
Let us analyze the assertion and reason:
- Assertion (A): "Hemolytic disease after mismatched blood transfusion is example of Type 2 hypersensitivity and may be sometimes with fatal outcome."
This statement is true. Type II hypersensitivity reactions occur when antibodies bind to antigen targets on cell surfaces.
A mismatched blood transfusion is a classic clinical example.
When a recipient receives incompatible donor red blood cells (RBCs), pre-existing antibodies in the recipient's serum immediately bind to the foreign antigens on the donor RBCs, causing massive intravascular hemolysis.
This can lead to acute renal failure, disseminated intravascular coagulation (DIC), and systemic shock, which can be fatal if not managed.
- Reason (R): "Type 2 hypersensitivity is mediated by IgG and IgM directed against antigens on circulating red blood cells that leads to cell lysis"
This statement is true. The immunological basis of Type II hypersensitivity involves circulating IgG or IgM antibodies directed against cell-bound or tissue-bound antigens.
Upon binding to antigens on the red blood cell surface, these antibodies activate the complement system via the classical pathway.
This leads to the formation of the membrane attack complex (MAC), causing direct osmotic lysis of the RBCs (complement-mediated lysis).
Alternatively, it can lead to opsonization and phagocytosis by macrophages in the spleen.
- Evaluating the Relationship:
The reason hemolytic transfusion reactions occur (the assertion) is precisely because pre-existing IgG or IgM antibodies in the recipient recognize and bind to the mismatched donor RBC antigens, initiating complement-mediated lysis (the reason).
Therefore, both statements are true, and the Reason (R) is the correct explanation of the Assertion (A).

Step 3: Final Answer:
Both (A) and (R) are true and (R) is the correct explanation of (A).
Therefore, the correct choice is Option (A).