Cell mediated immunity is mediated by

Options

A. B-lymphocytes
B. NK cells
C. T-lymphocytes
D. Plasma cells

Answer

**Step-by-Step Solution:**

1. **Understanding Cell Mediated Immunity**:
- Cell mediated immunity is a type of immune response that does not involve antibodies but rather the activation of immune cells to fight off pathogens.

2. **Identifying Key Players**:
- The primary cells involved in cell mediated immunity are T lymphocytes. These cells play a crucial role in identifying and destroying infected or cancerous cells.

3. **Types of T Lymphocytes**:
- Within T lymphocytes, there are different types, including cytotoxic T lymphocytes (CTLs) which are specifically responsible for killing infected cells.

4. **Activation of T Lymphocytes**:
- When an antigen (a substance that induces an immune response) is presented to T lymphocytes by antigen-presenting cells, these T cells become activated.

5. **Function of Activated T Lymphocytes**:
- Upon activation, cytotoxic T lymphocytes release various cytokines that help in neutralizing the antigen and coordinating the immune response.

6. **Evaluating the Options**:
- B lymphocytes: These are involved in humoral immunity, producing antibodies, so they are incorrect.
- NK cells: Natural Killer cells are part of the innate immune response, not cell mediated immunity, so they are incorrect.
- Plasma cells: These are differentiated B cells that produce antibodies, thus also part of humoral immunity, making them incorrect.
- T lymphocytes: These are indeed responsible for cell mediated immunity, making this the correct answer.

7. **Conclusion**:
- The correct answer to the question "Cell mediated immunity is mediated by" is T lymphocytes.

**Final Answer**: T lymphocytes

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