The antibody which can cross placental barrier is

Options

A. IgA
B. IgE
C. IgM
D. IgG.

Explanation

To answer the question "The antibody which can cross the placental barrier is:", we will analyze the different types of antibodies one by one.

### Step-by-Step Solution:

1. **Understanding Antibodies**: Antibodies, also known as immunoglobulins, are proteins produced by the immune system to identify and neutralize pathogens like bacteria and viruses.

2. **Identifying the Types of Antibodies**:
- **Immunoglobulin A (IgA)**: This antibody is primarily found in mucosal areas, such as saliva, tears, and breast milk (especially colostrum). It plays a crucial role in mucosal immunity but does not cross the placental barrier.

- **Immunoglobulin E (IgE)**: This antibody is present in very small amounts in the body and is primarily involved in allergic reactions. It triggers responses from mast cells but does not cross the placental barrier.

- **Immunoglobulin M (IgM)**: This is the first antibody produced in response to an infection. It is large in size and effective in trapping pathogens but does not cross the placental barrier due to its size.

- **Immunoglobulin G (IgG)**: This is the most abundant antibody in the body, accounting for about 70-80% of the total immunoglobulins. Crucially, IgG is the only antibody that can cross the placental barrier, providing passive immunity to the fetus during pregnancy.

3. **Conclusion**: Based on the analysis of the different types of antibodies, the only antibody that can cross the placental barrier is **Immunoglobulin G (IgG)**.

### Final Answer:
The antibody which can cross the placental barrier is **Immunoglobulin G (IgG)**.

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