Stem Cell

Developmental Scheme of Stem Cells

Stem Cells

↓

Progenitor Cells

↓

Precursor Cells

↓

Mature Cells

Developmental Scheme (Proliferation and Potential)

Cells                 Prolif                     Potential

Stem Cells           +                            ++++

Progenitor Cells    ++++                         ++

Precursor Cells      +++                        Single

Mature Cells          +/-                          Single

Hematopoietic Stem Cell

-The hematopoietic stem cell divides to replace itself and produce a progenitor cell with the potential to give rise to all of the hematopoietic lineages, by generating further progenitor cells committed to progressively narrower ranges of differentiated fates.

-Both the red and the white blood cells are believed to be derived from a common hematopoietic stem cell (HSC) via committed progenitors  that give rise to the erythroid, myeloid and lymphoid lineages

Erythroid Lineage

-gives rise to the erythrocytes and to megakaryocytes which shed fragments that form the platelets that initiate blood clotting

Myeloid Lineage 

-gives rise to the phagocytic and inflammatory cells of innate immunity

ex. mast cell,  neutrophil, basophil, monocytes(which give rise to macrophages and dendrites)

- also gives rise to dendritic cells

Lymphoid Lineage

- The lymphoid lineage gives rise to the T and B cells of adaptive immunity and to natural killer (NK) cells which are specialized cytotoxic cells.

- Also gives rise to dendritic cells

Regulation of Hematopoiesis 

1.  Bone marrow-resident stromal cells make cytokines that control and direct hematopoietic cell growth and differentiation.

2.  Movement of developing cells from one microenvironment to another exposes the cells to new combinations of cytokines.

3.  Production of cytokines by activated T cells and macrophages in response to infection by pathogens.

4.  Up- or down regulation of cytokine receptor expression by developing hematopoietic cells.  This is essential for determining how the cell is able to respond to its microenvironment and it is a critical factor in the process of lineage commitment of the developing cell.

5.  Removal of developing (as well as mature) cells by apoptosis.

Key Early Cytokines

Key Late Cytokines