Which of the following antibody can be characterized by the following features ?
1. It is the heaviest antibody.
2. The first antibody which come into action after entry of the pathogen.
3. It is a pantamer.

Options

A. lgA
B. lgC
C. lgM
D. lgE

Answer

To solve the question regarding the characteristics of a specific antibody, we will analyze each option based on the given features:

1. **Identify the Characteristics**:
- The antibody in question is the heaviest antibody.
- It is the first antibody that comes into action after the entry of a pathogen.
- It is a pentamer, meaning it consists of five subunits.

2. **Evaluate Each Option**:
- **Option 1: IgA**:
- IgA is primarily found in mucosal areas and is not the heaviest antibody. It does not fit the criteria of being the first responder or a pentamer.
- **Option 2: IgG**:
- IgG is the most abundant antibody in serum but is not the heaviest and is not the first antibody produced in response to an infection. It is also not a pentamer.
- **Option 3: IgM**:
- IgM is known to be the heaviest antibody due to its pentameric structure, consisting of five antibody units. It is also the first antibody produced in response to an infection, making it the correct choice.
- **Option 4: IgE**:
- IgE is involved in allergic reactions and does not fit any of the specified characteristics.

3. **Conclusion**:
- Based on the analysis, the correct answer is **IgM**. It is the heaviest antibody, the first to respond to pathogens, and has a pentameric structure.

### Final Answer:
The antibody characterized by the given features is **IgM**.