Which antigen is responsible for erythroblastosis foetalis?

Options

A. Antigen A
B. Antigen B
C. Rh antigen
D. Antigen O

Answer

**Step-by-Step Solution:**

1. **Understanding Erythroblastosis Fetalis:**
- Erythroblastosis fetalis is a medical condition where the fetus suffers from hemolytic anemia, which is the destruction of red blood cells (RBCs).

2. **Identifying the Cause:**
- This condition occurs when there is an incompatibility between the blood types of the mother and the fetus. Specifically, it arises when the mother is Rh-negative and the fetus is Rh-positive.

3. **Role of the Rh Antigen:**
- The Rh antigen is a specific protein found on the surface of red blood cells. If the fetus inherits the Rh-positive blood type from the father, it will have the Rh antigen.

4. **Immune Response:**
- The mother’s immune system recognizes the Rh-positive antigen as a foreign substance because she is Rh-negative. As a response, she produces antibodies against the Rh antigen.

5. **Crossing the Placenta:**
- These antibodies can cross the placenta and enter the fetal circulation. When they encounter the Rh-positive RBCs of the fetus, they bind to the Rh antigen.

6. **Destruction of Fetal RBCs:**
- The binding of maternal antibodies to fetal RBCs leads to their destruction (hemolysis), resulting in hemolytic anemia in the fetus, which is the hallmark of erythroblastosis fetalis.

7. **Conclusion:**
- Therefore, the antigen responsible for erythroblastosis fetalis is the Rh antigen.

**Final Answer:**
The Rh antigen is responsible for erythroblastosis fetalis.

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