Question

Lymphocyte Development 1. B cell development in the bone marrow shares may features with T cell development in the thymus. A) Discuss what you consider to be the two major goals of lymphocyte development (i.e, what is the purpose of the Bone marrow and Thymus environments). B) Describe what occurs during the Precursor B cell stage and identify/describe the analogous stage in T cells.

Answer 1

A) The main goals of lymphocyte development are to ensure that all T-lymphocytes have functional T-cell receptor (or TCR) and to ensure self tolerated cells by deleting the autoreactive cells.

Thymus undergo a process of maturation, which involves ensuring the cells react against antigens, that is positive selection, but that they do not react against antigens found on body tissue (negative selection).T-lymphocytes are develop from stem cells in the bone marrow and migrate to the thymus to provide vital functions in the immune system and here they are known as thymocytes.

B cell development begins in the foetal liver and continues by haematopoietic cells in the bone marrow throughout our lives. B cell development occurs when lymphoid progenitor cells receive signals from bone marrow stromal cells.

B) The dividing B cells are larger than other resting cells and this dividing stage is called as the large precursor B cell or pre-B cell stage. And the small undividing B cells are known as small pre-B cells.

Stage of Maturation Stem cell Pro- Pre Immature lymphocyte lymphocyte lymphocyte Mature lymphocyte Differentiated effector lymphocyte

Both T cells and B cells undergo series of stages before maturation. These cells have precursor stage and mature stage in their development.