What class of antibodies are responsible for the condition - erythroblastosis fetalis?

Options

A. lgA
B. lgM
C. lgD
D. lgG

Answer

**Step-by-Step Solution:**

1. **Understanding Erythroblastosis Fetalis**: Erythroblastosis fetalis is a condition that occurs when there is an incompatibility between the blood types of a mother and her fetus, specifically concerning the Rh factor.

2. **Rh Factor Compatibility**: In this condition, the mother typically has a negative Rh factor (Rh-) and the father has a positive Rh factor (Rh+). If the first child inherits the Rh+ factor from the father, the mother’s immune system may produce antibodies against the Rh factor.

3. **Antibody Production**: When the mother’s blood comes into contact with the Rh+ blood of the fetus during delivery, her immune system recognizes the Rh+ factor as foreign and produces antibodies against it. This process primarily involves the production of immunoglobulins.

4. **Types of Immunoglobulins**: There are several classes of immunoglobulins produced by B lymphocytes: IgG, IgA, IgM, IgD, and IgE. Each has different roles in the immune response.

5. **Identifying the Relevant Antibody**: The key point is that the antibodies produced by the mother that can cross the placenta and affect the fetus in subsequent pregnancies are of the IgG class. IgG is the smallest and most abundant antibody in the bloodstream, allowing it to cross the placental barrier.

6. **Conclusion**: Therefore, the class of antibodies responsible for erythroblastosis fetalis is IgG.

**Final Answer**: The class of antibodies responsible for erythroblastosis fetalis is **IgG**.

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