Which is a circulating antibody and protect the body from bacterial and viral infection?

Options

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

Answer

To determine which antibody circulates in the body and protects against bacterial and viral infections, we can follow these steps:

### Step 1: Understand the Types of Antibodies
There are several types of antibodies, known as immunoglobulins, which include IgD, IgE, IgG, and IgA. Each type has different functions and roles in the immune response.

### Step 2: Identify the Function of Each Antibody
- **IgD**: Primarily functions as a receptor on B cells and is not significantly involved in direct immune responses.
- **IgE**: Mainly associated with allergic reactions and protection against parasitic infections.
- **IgG**: The most abundant antibody in the blood and extracellular fluid, it plays a crucial role in the immune response against both bacterial and viral infections.
- **IgA**: Found in mucosal areas and bodily secretions, it primarily protects against pathogens entering through mucosal surfaces but is less effective against systemic infections.

### Step 3: Analyze the Question
The question specifically asks for an antibody that circulates in the body and protects against both bacterial and viral infections.

### Step 4: Compare the Options
From the analysis:
- IgG is known for its ability to neutralize pathogens and is effective against both bacteria and viruses.
- IgA, while important, does not circulate in the blood as much as IgG and is more focused on mucosal immunity.

### Step 5: Conclusion
Based on the information gathered, the antibody that circulates in the body and protects against both bacterial and viral infections is **IgG**.

### Final Answer
**C. Immunoglobulin G (IgG)**

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