How many classes of immunoglobulins are there in humans?

Options

A. 3
B. 4
C. 5
D. 6

Answer

To answer the question "How many classes of immunoglobulins are there in humans?", we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Immunoglobulins**:
- Immunoglobulins, also known as antibodies, are glycoproteins secreted by plasma cells in response to antigens.
- They play a crucial role in the immune response by neutralizing pathogens.

2. **Identifying the Classes**:
- There are five distinct classes (or isotypes) of immunoglobulins in humans.
- These classes are:
- **IgM (Immunoglobulin M)**: The first antibody produced during an immune response.
- **IgD (Immunoglobulin D)**: Primarily functions in the initiation of B cell activation.
- **IgA (Immunoglobulin A)**: Found in mucosal areas and secretions like saliva and tears.
- **IgE (Immunoglobulin E)**: Involved in allergic reactions and responses to parasitic infections.
- **IgG (Immunoglobulin G)**: The most abundant antibody in circulation, capable of crossing the placenta to provide immunity to the fetus.

3. **Conclusion**:
- Therefore, the total number of classes of immunoglobulins in humans is **five**.

### Final Answer:
The number of classes of immunoglobulins in humans is **five**.

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