Hematopoiesis - Tissue Functioning and Remodeling in the Circulatory and Ventilatory Systems - page 21

multi- and unipotent stem cells (USC) to the different lineages via proerythroblasts
and erythroblasts, megakaryoblasts, myeloblasts and promyelocytes, and lym-
phoblasts.

2.1 Hematopoietic Stem Cells

Hematopoietic stem cells (HSC) generate a set of progenitors for erythroid,
lymphoid, megakaryocytic, and myeloid lineages. Another type of multipotent cells
resides in the bone marrow — mesenchymal stem cells — that can differentiate into
osteoblasts, chondrocytes, and adipocytes. Most primitive hematopoietic stem cells
are quiescent.
Two subpopulations of hematopoietic stem cells exist: (1) long-term quiescent
(reserve) and (2) active hematopoietic stem cells [ 40 ]. In the bone marrow, endosteal
regions composed of osteoblasts, osteoclasts, as well as vascular and CXCL12 high
reticular cells, and central regions that lack osteoblasts form inhibitory and stim-
ulatory (proliferative) zones, respectively. These 2 adjoining, but separate regions
enable the coexistence of 2 different subpopulations (states) of hematopoietic stem
cells.
The pool of hematopoietic stem cells comprises clonal subtypes with different
lineage potential and self-renewal capacity. Aging affects the function and com-
position of mature blood cell compartments with a decline in lymphoid lineage
potential and increased myeloid lineage commitment [ 41 ]. The gene program that
specifies lymphoid fate is downregulated with age. Myeloid-biased hematopoietic
stem cells produce high levels of signaling lymphocytic activation molecule family

Tabl e 2. 1. Members of the signaling lymphocytic activation molecule family (SLAMF) of
immune receptors, or cluster of differentiation CD2 receptor family. They are synthesized
in various subsets of immunocytes (T, B, and NK cells; BLAME: B-lymphocyte activator
macrophage-expressed membrane protein; BLAST: B-lymphocyte activation surface marker;
CD2F: CD2 family member; CD84H: CD84 homolog; CRACC: CD2-like receptor activating
cytotoxic cells; CS: CD2 subset; Ly: lymphocyte surface antigen; NAIL: NK-cell activation-
inducing ligand; NKR: NK-cell type-1 receptor; nLy: novel lymphocyte antigen; NTBA: natural
killer-, T-, and B-cell antigen; SF: signaling lymphocytic activation molecule family member).

Member Other aliases

SLAMF1 CD150, SLAM

SLAMF2 CD48, BLAST1

SLAMF3 CD229, Ly9

SLAMF4 CD244, NAIL, NKR2B4

SLAMF5 CD84, Ly9 β

SLAMF6 CD352, Ly108, NTBA, SF2000

SLAMF7 CD319, nLy9, CRACC, CS1

SLAMF8 CD353, BLAME

SLAMF9 CD2F10, CD84H1, SF2001