Which one of the following is true for T-lymphocytes?

Options

A. They cannot release antibodies.
B. They mature in lymph nodes.
C. They comprise `10-15%` of lymphoctyes.
D. They are principle cells in lymph nodes' cortical center.

Answer

### Step-by-Step Solution:

1. **Understanding T-Lymphocytes**: T-lymphocytes, also known as T cells, are a type of white blood cell that plays a central role in the immune response. They are involved in cell-mediated immunity and help regulate the functions of other immune cells.

2. **Function of T-Lymphocytes**: T-lymphocytes produce cytokines, which are signaling proteins that aid in the immune response. Cytokines help in the differentiation of B cells into plasma cells, which are responsible for producing antibodies.

3. **Analyzing the Options**:
- **Option 1**: "They cannot release antibodies." This statement is false because T-lymphocytes help in the production of antibodies indirectly by facilitating B cell differentiation.
- **Option 2**: "They mature in lymph nodes." This is incorrect as T-lymphocytes mature in the thymus, not in the lymph nodes.
- **Option 3**: "They comprise 10-15% of the lymphocytes." This is also incorrect because this percentage refers to B lymphocytes, not T lymphocytes.
- **Option 4**: "They are the principal cells in the lymph nodes of the cortical centers." This statement is true as T-lymphocytes are indeed found in the lymph nodes and play a crucial role in the immune response.

4. **Conclusion**: The correct answer is that T-lymphocytes are the principal cells in the lymph nodes of the cortical centers.