Hematopoiesis - Tissue Functioning and Remodeling in the Circulatory and Ventilatory Systems - page 25

Granulocyte-macrophage progenitors generate myelomonocytic and megakaryo-
cytic-erythrocyte progenitors. However, the separation between the myeloid and
megakaryocytic-erythroid cell lineages can occur before the development of
common myeloid progenitors.
Myelo-erythroid progenitors include pregranulocyte-macrophage precursors that
give rise to granulocyte-macrophage progenitors, whereas prepremegakaryocytic-
erythroid precursors yield preCFUe (CFU erythroid), CFUe, and megakaryocytic-
platelet (MKP) compartments.

2.2.1 Arborescence Models of Hematopoiesis

An arborescence model of hematopoiesis assumes branches for the differentiation
of blood cells [ 55 ]. This model states that: (1) megakaryocytes as well as erythroid
and myeloid cells from a multipotent progenitor (MPP), lymphoid-primed multi-
potent progenitor (LMPP), early lymphoid progenitor (ELP), or common myeloid
progenitor (CMP); and (2) natural killer cells and B and T lymphocytes from a
common lymphoid progenitor (CLP).
Another tree-like model supposes that: (1) a common myeloid-lymphoid progeni-
tor (CMLP) gives rise to (1.1) a myeloid-T-cell progenitor (MTP) that differentiates
into myeloid and T lymphocytes and (1.2) myeloid-B-cell progenitor (MBP) that
gives rise to myeloid and B lymphocytes; and (2) a common myeloid progenitor
generates myeloid cells and a myeloid-erythroid progenitor (MEP), a source of
erythroid cells and megakaryocytes.
A third model proposes that erythroid potential is lost early from a common
myeloid progenitor that differentiates into granulocyte-monocyte progenitor (GMP)
with myeloid potential and myeloid-erythroid progenitor , whereas a common
lymphoid progenitor leads to lymphoid cells.

Arborescence Model Drawbacks

Lymphoid progenitors can have a myeloid potential and differentiate into myeloid
cells (macrophages and dendritic cells). Therefore, models of early segregation of
lymphoid and myeloid differentiation axes are not validated by observations.

2.2.2 Lymphoid Progenitors

− + + +

Most Lin lymphoid-primed multipotent progenitors

lack erythroid and megakaryocytic potential. Several lymphoid progenitors that are
able to generate B and T lymphocytes and natural killer cells include: (1) Lin

,SCA1 ,SCFR ,FLT3

−

,

,FLT3 high ,VCAM1

+ + −

SCA1 ,SCFR lymphoid-primed multipotent progenitors;