Question

T-lymphocytes are
A. Formed in thymus
B. Formed in bone marrow and mature in thymus
C. Formed in thymus and preprocessed in bone marrow
D. Formed and preprocessed in bone marrow

Answer 1

Hint: T-lymphocytes are the type of White Blood Cells or WBC’s. T-lymphocytes are important components of the body’s immune system. T-lymphocytes are also known as T cells.

Complete answer:
• T-lymphocytes are small cells with a diameter of about 8 to 10 micrometers. They contain a large nucleus which encloses dense hetero-chromatin. They also contain a small number of mitochondria, ribosomes, and lysosomes.
• T-lymphocytes act via cell mediated immunity. It involves direct destruction of the infected cell and release of chemicals to activate other cells of the immune system to destroy the pathogen or infected cell.
• T-lymphocytes are formed from the Hematopoietic Stem Cells (HSCs) in the following process:
- The Hematopoietic Stem Cells (HSCs) are present in the bone marrow. HSCs undergo division and differentiation to produce lymphoid stem cells.
- The lymphoid stem cells undergo morphological changes such as reduction in cell size and produce immature lymphocytes and lymphoblasts.
- Lymphoblasts or immature lymphocytes are released into the bloodstream from bone marrow. Once inside the bloodstream, they are transported to the thymus gland in the neck. Lymphoblasts are now called thymocytes. Thymocytes undergo further maturation and number of selection processes in thymus. All these processes lead to the formation of mature T-lymphocytes.
- As this final maturation of lymphocytes happens inside thymus, they are known as T-lymphocytes or T cells (T stands for thymus).
- Thus, the T-lymphocytes are formed in bone marrow and mature in thymus.

Hence, the correct answer is option (B).

Note: T-lymphocytes belong to White Blood Cells or WBC’s. They are produced from Hematopoietic Stem Cells (HSCs) of bone marrow and undergo final maturation in thymus. Lymphocytes such as B-cells and T-cells are produced in the bone marrow.