Which of the following is incorrect regarding T-cells ?

Options

A. These play important role in cell mediated immunity.
B. These play an important role in activation of B-lymphocytes.
C. These are a type of lymphocytes.
D. These are not responsible for graft rejection.

Answer

To determine which statement is incorrect regarding T-cells, we will analyze each option provided in the question.

### Step-by-Step Solution:

1. **Understanding T-cells**:
- T-cells are a type of lymphocyte that plays a crucial role in the immune response, particularly in cell-mediated immunity. They are developed in the thymus gland.

2. **Evaluating the Options**:
- **Option 1**: "This plays an important role in cell-mediated immunity."
- This statement is **correct**. T-cells are indeed essential for cell-mediated immunity, which involves the direct attack on infected cells.

- **Option 2**: "This plays an important role in the activation of B lymphocytes."
- This statement is also **correct**. T-helper cells (a subtype of T-cells) are involved in activating B-cells, which produce antibodies.

- **Option 3**: "These are a type of lymphocytes."
- This statement is **correct**. T-cells are classified as lymphocytes, which are a type of white blood cell involved in the immune response.

- **Option 4**: "These are not responsible for graft rejection."
- This statement is **incorrect**. T-cells are indeed involved in graft rejection, as they can recognize foreign tissues and mount an immune response against them.

3. **Conclusion**:
- The incorrect statement regarding T-cells is **Option 4**: "These are not responsible for graft rejection."

### Final Answer:
The incorrect statement regarding T-cells is that they are not responsible for graft rejection.

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