Blood Cells - Tissue Functioning and Remodeling in the Circulatory and Ventilatory Systems - page 172

dendritic cells, the so-called Langerhans cells , that are not replaced by blood-borne
cells in the absence of infection [ 296 ]. 183
Dendritic cells produce the lysosomal cysteine peptidase, cathepsin-K, that
regulates Toll-like receptor-9 and release pro-inflammatory cytokines to mediate
immune responses [ 312 ]. In particular, they attenuate activation of helper-17 T cells.
FoxP3 , regulatory T cells that prevent overproduction of reactive

immunocytes to avoid autoimmune disease preclude T-lymphocyte activation and
production of CD80 184 and CD86 185 on dendritic cells, which are costimulatory
or coinhibitory molecules of CD28 on T lymphocytes. Both CD80 and CD86
coreceptors present foreign antigens to immunocytes. Cytotoxic T-lymphocyte
antigen CTLA4 produced by regulatory T cells enables these cells to repress CD80
and CD86 expression on dendritic cells [ 313 ].

+ ,CD4 +

3.14.1 Myeloid and Plasmacytoid Dendritic Cells

Several dendritic cell subsets exist with distinct immunological activities, tissue
distribution, and migratory properties. Different subsets of dendritic cells are
defined according to cellular origin, location, function, and lifespan in peripheral
tissues, particularly in the spleen (where they have a relatively short life) and lymph
nodes.
Conventional dendritic cells originate from bone marrow-derived myeloid pre-
cursors for monocytes and dendritic cells [ 311 ]. Inflammatory dendritic cells , born
from monocytes during inflammation, migrate to lymphoid organs. Plasmacytoid
dendritic cells , which produce large amounts of type-1 interferon, may derive
at least partially from myeloid progenitors. Antigen-presenting Langerhans cells ,
located in the skin, may be generated from skin-resident progenitors.
Myeloid and plasmacytoid dendritic cells are the main producers of

interferon- . The fetal liver kinase FLK2, or stem cell receptor protein Tyr kinase

STK1 186 is required for the development of classical and plasmacytoid dendritic
cells [ 296 ].
In lungs, among other sites, 2 distinct populations of dendritic cells exist [ 296 ]:
(1) CD103

α

+ ( α E -integrin) and (2) slight T-cell stimulatory CX3CR1 + dendritic

cells.
In the bone marrow, macrophage-dendritic cell progenitors (MDP) gener-
ate common dendritic cell precursors (CDP) that give rise to preclassical and

183 Langerhans cells develop from an embryonic precursor that colonizes the epidermis before
birth, differentiates in situ, and then proliferates during the first week of life to constitute the
pool of Langerhans cells [ 296 ]. Langerhans cells self-renew and can massively proliferate during
inflammation.
184 A.k.a. CTLA4 counter-receptor B7.1.
185 A.k.a. CTLA4 counter-receptor B7.2.
186 Not Ser/Thr kinase-1. A.k.a. Fms-related Tyr kinase FLT3 and CD135.