Biomedical Engineering Reference
In-Depth Information
Neutrophils, major effector cells in innate immunity against bacteria, undergo
platelet-dependent activation in the vasculature during bacteremia. They can form
neutrophil extracellular traps that consist of chromatin coated with peptidases to
trap and kill bacteria within the vasculature. Complement activation, specifically
anaphylatoxin C5a, contributes to the recruitment of neutrophils in particular to the
lung [
97
].
3.3
Proliferation and Mobilization of Blood Cells
Blood cell genesis, growth, proliferation in their bone marrow niches, and mobi-
lization in the blood stream and in the body's tissues are regulated by numerous
substances (Vol. 2 - Chaps. 2. Cell Growth and Proliferation and 6. Cell Motility).
Blood cells need to communicate between them and with other body's cells.
They secrete
cytokines
that have a broad activity spectrum. Cytokines allow com-
munications between immunocytes as well as between immunocytes and other cell
types. They thus target manifold cell types.
Chemokines
are inducible chemotactic
cytokines, which mobilize nearby responsive cells according to a chemotactic
direction (Vol. 2 - Chap. 6. Cell Motility and Chaps.
10
and
11
).
Three main action modes are used via suitable receptors according to the length
scale: (1)
intracrine
2
and
autocrine
3
mechanisms act on the producing cell without
or after secretion, respectively; (2)
juxtacrine
4
and
paracrine
5
regulation happens on
apposed and neighboring cells, respectively; and (3)
endocrine
6
activity is exerted
on remote cells.
3.3.1
Cytokines
Cytokines are growth factors implicated in immunity and hematopoiesis (Table
3.2
;
Chap.
2
; Vol. 2 - Chap. 3. Growth Factors)). Cytokines exhibit both pleiotropy
and redundancy. Pleiotropic actions of cytokines can be explained by the presence
of receptors for a given cytokine on multiple cell lineages and the activation
of multiple signaling pathways contributing to different functions. Overlapping
actions of different cytokines can be explained by similar cellular distributions of
specific receptors for different cytokines, as well as by share of signaling pathways.
2
Latin intra: within.
3
Greek
o: inside.
4
Latin juxta: immediately adjacent, adjoining.
5
Greek
αυτ
παρα
: close to.
6
Greek
νδ
κρινω
o
: release inside.
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