Antigen Presenting Cells (APCs)
387
10.1
DC Subsets
Phagocytic
cells
carrying
numerous
dendrites
and
expressing
considerable
amounts
of
MHC
and
costimulatory
molecules in their unactivated state are
found in distinct microenvironments of
our
body,
for
example,
in
peripheral
tissues,
in
lymph
nodes,
and
in
the
thymus. In addition, DCs do not only
interact with T cells, but also with B
cells and with NK cells. These aspects
render it most likely that the various
and often opposing functions ascribed to
DCs can only be performed by different
sets of DCs. According to the functional
plasticity model, only a single DC lineage
(hematopoietic precursor, DC precursor,
immature DC, mature DC) exists and local
environmental factors cause functional
diversity
(Fig. 10).
According
to
the
specialized
lineage
model,
however,
specialized DC subtypes are the product of
entirely separate developmental lineages,
with
DC
precursors
being
already
functionally committed. It appears that in
reality, we are facing a complicated mixture
of both models.
10.1.1
Myeloid Versus Lymphoid DCs
Distinct DC subtypes were initially more
evident among mouse DCs than among
human DCs because of the availability of
Functional plasticity
model
Specialized lineage
model
DC1
DC2
pDC1
pDC2
pDC
DC
precursors
DC
subsets
Hematopoietic
precursor
1
1
2
2
Fig. 10
Generation of functionally distinct DC subsets. According to the
functional plasticity model, all DCs belong to a single hematopoietic lineage,
the subtypes DC1 and DC2 being generated by local environmental factors in
the periphery (1). The specialized lineage model proposes that DC subsets
originate from early divergences in the development, triggered by the
microenvironment of the bone marrow (2), giving rise to distinct precursors,
pDC1 and pDC2. Subsequently, pDC1 and pDC2 function as the precursors of
the DC1 and DC2 subsets respectively.
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