Antibody formed of five immunoglobin units/pentamer is

Options

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

Answer

To answer the question regarding which antibody is formed of five immunoglobulin units (pentamer), we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Structure of Antibodies**: Antibodies, also known as immunoglobulins, are glycoproteins produced by plasma cells. They play a crucial role in the immune response.

2. **Identify the Types of Immunoglobulins**: There are five main types of immunoglobulins:
- IgM (Immunoglobulin M)
- IgG (Immunoglobulin G)
- IgA (Immunoglobulin A)
- IgD (Immunoglobulin D)
- IgE (Immunoglobulin E)

3. **Examine the Structure of Each Immunoglobulin**:
- **IgM**: This is the only immunoglobulin that is pentameric, meaning it consists of five subunits.
- **IgG**: This immunoglobulin is monomeric, meaning it consists of a single unit.
- **IgA**: This can exist as a monomer or dimer but not as a pentamer.
- **IgD**: This is also monomeric.
- **IgE**: This is monomeric as well.

4. **Conclusion**: Since the question specifically asks for the antibody that is formed of five immunoglobulin units, the correct answer is **IgM**.

### Final Answer:
The antibody formed of five immunoglobulin units (pentamer) is **IgM**.

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