An antibody is a

Options

A. White corpuscle which attacks invading bacteria
B. Molecule that specifically inactivates an antigen
C. Component of the blood
D. Secretion of mammalian erythrocyte

Answer

**Step-by-Step Solution:**

1. **Understanding Antibodies**: Antibodies are proteins produced by the immune system in response to foreign substances called antigens. They are also known as immunoglobulins (Ig).

2. **Production of Antibodies**: When the body detects antigens (which can be pathogens like bacteria or viruses), it triggers an immune response that leads to the production of antibodies.

3. **Function of Antibodies**: Antibodies bind specifically to antigens. This binding initiates several immune responses aimed at neutralizing or destroying the antigen.

4. **Types of Reactions**: The interactions between antibodies and antigens can lead to various reactions, including:
- **Agglutination**: Clumping of pathogens.
- **Opsonization**: Marking pathogens for destruction by immune cells.
- **Precipitation**: Formation of insoluble complexes.
- **Neutralization**: Blocking the harmful effects of toxins or pathogens.
- **Lysis**: Rupturing the cell membrane of pathogens.

5. **Conclusion**: The primary role of antibodies is to inactivate or neutralize antigens, thereby protecting the body from infections. Therefore, the most accurate definition of an antibody is that it is a molecule that specifically inactivates an antigen.

**Final Answer**: An antibody is a molecule that specifically inactivates an antigen.

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