Cytotoxid T cells are known for their ability to unite with

Options

A. human tissue cells
B. bacteria and viruses
C. MHC I bound antigen
D. small molecules known as epitopes

Answer

### Step-by-Step Solution:

1. **Understanding Cytotoxic T Cells**: Cytotoxic T cells are a type of immune cell that plays a crucial role in the body's defense against pathogens. They are responsible for identifying and destroying infected or cancerous cells.

2. **Function of Cytotoxic T Cells**: These cells release substances called cytokines, which help in the destruction of infected cells, including those infected by bacteria and viruses. They are particularly effective against cells that display abnormal antigens, such as those from pathogens.

3. **Identifying the Correct Answer**: The question asks with what cytotoxic T cells unite. The options provided include:
- Human tissue cells
- Bacteria and viruses
- MHC1 bound antigen
- Small molecules known as epitopes

4. **Evaluating Each Option**:
- **Human Tissue Cells**: Cytotoxic T cells do not unite with healthy human tissue cells; they target infected or damaged cells.
- **Bacteria and Viruses**: Cytotoxic T cells are known for their ability to attack and destroy cells infected by bacteria and viruses. This is the correct answer.
- **MHC1 Bound Antigen**: While cytotoxic T cells recognize antigens presented by MHC1 molecules, they do not unite with them in a physical sense.
- **Small Molecules Known as Epitopes**: Epitopes are parts of antigens that antibodies bind to, but cytotoxic T cells do not directly unite with epitopes.

5. **Conclusion**: Based on the analysis, the correct answer is that cytotoxic T cells are known for their ability to unite with **bacteria and viruses**.