Predominant early antibody that first activates in primary immune response is

Options

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

Answer

To solve the question regarding the predominant early antibody that first activates in the primary immune response, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Primary Immune Response**:
- The primary immune response is the body's initial reaction to a specific antigen when it is encountered for the first time. This response involves the activation of various immune cells and the production of antibodies.

2. **Identify the Types of Antibodies**:
- There are several types of antibodies (immunoglobulins) produced by the immune system, including IgG, IgA, IgD, and IgM. Each has different roles and characteristics.

3. **Evaluate Each Option**:
- **Option A: IgG** - This antibody is primarily involved in the secondary immune response and is known for its ability to cross the placenta and provide immunity to the newborn. It is not the first antibody produced in response to an antigen.
- **Option B: IgA** - This antibody is mainly found in mucosal areas and plays a crucial role in mucosal immunity. It is not the predominant antibody in the primary immune response.
- **Option C: IgD** - This antibody is primarily involved in the activation of B cells and does not play a significant role in the initial response to an antigen.
- **Option D: IgM** - This is the correct answer. IgM is the first antibody produced in response to an antigen during the primary immune response. It is the predominant early antibody that activates in this phase.

4. **Conclusion**:
- After evaluating all the options, it is clear that IgM is the predominant early antibody that first activates in the primary immune response.

### Final Answer:
The predominant early antibody that first activates in the primary immune response is **IgM**.