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 pentamer.

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 of the provided features step by step.

### Step 1: Identify the Heaviest Antibody
The first feature states that the antibody is the heaviest. Among the different classes of antibodies (IgG, IgA, IgM, IgE, and IgD), IgM is known to be the heaviest due to its structure and size.

**Hint:** Remember that the weight of antibodies varies, and IgM is the largest in size and weight.

### Step 2: First Antibody to Respond
The second feature mentions that it is the first antibody that comes into action after the entry of a pathogen. IgM is typically the first antibody produced in response to an infection. It is generated shortly after the exposure to an antigen.

**Hint:** Consider the immune response timeline; IgM is the first responder in the primary immune response.

### Step 3: Pentamer Structure
The third feature indicates that the antibody is a pentamer. IgM has a pentameric structure, meaning it is composed of five monomer units linked together. This structure allows it to effectively bind to multiple antigens simultaneously.

**Hint:** Think about the structural forms of antibodies; pentamer means five units working together.

### Conclusion
Based on the analysis of the three features, we conclude that the antibody characterized by being the heaviest, the first to respond after pathogen entry, and having a pentameric structure is **IgM**.

**Final Answer:** IgM antibody