What are plasma cells?

Explanation

**Step-by-Step Solution:**

1. **Definition of Plasma Cells**: Plasma cells are a type of white blood cell that plays a crucial role in the immune response. They are derived from B-lymphocytes (B-cells) and are responsible for producing antibodies.

2. **Role of Antigens**: When a foreign substance, known as an antigen, enters the body, it triggers an immune response. Antigens are typically proteins found on the surface of pathogens like bacteria and viruses.

3. **Activation of T-helper Cells**: The presence of an antigen activates T-helper cells, which are a subtype of lymphocytes. These T-helper cells recognize the antigen and signal B-cells to respond.

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