Question

What Happens in Lymphopoeisis in the embryo up until the lymphocyte maturation stage. Please give a detailed answer

Answer 1

Hematopoiesis describes the formation of blood cells.

During development, it occurs in yolk sac, liver and spleen and subsequently in red bone marrow in the medullary cavity of all bones.

All blood cells are derived from hematopoietic pluripotent stem cells. It give rise to a myeloid progenitor cell and lymphoid progenitor cell.

Lymphopoiesis
Lymphopoiesis refers to the production of new lymphocytes. They are produced from lymphoid progenitor cell.

Lymphocytes are of 3 main types.
1.T-lymphocyte(mediate cellular immunity)

2. B-lymphocyte(mediate humoral immunity)

3. Natural killer cells(NK cells)

Lymphocytes are derived from lymphoid progenitor cells within bone marrow.

**Development of B cells

Formation and maturation of B cells occur in bone marrow.

B lymphocyte development occurs in two phases

1. antigen-independent phase - in bone marrow and ileal Peyer's patches (development of B progenitor cells from non-B progenitor cells)
2. antigen-dependent phase - in peripheral lymphoid tissues

development of B progenitor cells is mediated regulatory cytokines such as IL-1, IL-2, IL-4, IL-10 and interferon gamma.

B cells migrate to peripheral lymphoid tissues like lymph node from where it is introduced to an antigen that it can recognize.

Early B cell development includes:

Stem cell--> Early pro-B cell--> Late pro-B cell--> Large pre-B cell-->Small pre-B cell--> Immature B cell

Transitional B cell development includes

Immature B cell--> T1 B cell--> T2 B cell--> Marginal zone B cell and mature B cell.

**Development of T cells

T-lymphocytes derive from the lymphoid progenitor cells in the bone marrow. This is mediated by several cytokines like IL-1, IL-2, and IL-9.

Then T lymphocyte progenitor cells migrate from the bone marrow to thymus. They undergo differentiation and maturation processes in thymus.

Upon maturation, they are derived into several types of cell:

• T helper cell
• T cytotoxic cell
• T memory cell
• T suppressor cell

** Develpoment of NK cell

Development and maturation occurs in the bone marrow.

Then the get released into the blood.
They don't have antigen specific receptors.