Biomedical Engineering Reference
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On the other hand, regulatory T cells in the draining mediastinal lymph nodes
can attenuate iBALT development. The majority of cells within BALT are IgM
low
,
IgD
high
,
11
plasmocytes can
also lodge in BALT according to the nature of the antigen. Follicular dendritic cells
in BALT present antigen to B lymphocytes and yield costimulatory signals that
enhance B-cell activation and proliferation in the germinal centers [
324
].
Activated pulmonary epithelial cells synthesize many pattern recognition recep-
tors (e.g., TLR1-TLR9) and secrete multiple cytokines, chemokines, and growth
factors that trigger recruitment and local proliferation of immune cells. Therefore,
at least 3 events can initiate BALT formation [
324
]: (1) activation of innate
pattern-xrecognition receptors such as TLRs; (2) inflammatory cytokines, such as
TNF
B lymphocytes. Nonetheless, IgG1
+
IgA
+
,andIgE
+
(TNFSF1), TNFSF2, and TNFSF3, and lymphoid chemokine production
by hematopoietic or stromal cells; and (3) activation and maturation of antigen-
presenting cells and development of high endothelial venules. Interleukin-6 with its
cognate receptor IL6R also leads to BALT formation.
Bronchial epithelial cells and T-cell-zone fibroblastic reticular cells synthesize
CCR7 ligands CCL19 and CCL21 [
324
]. Chemokine CCL21 localizes to endothe-
lial cells and reticular cells on the periphery of follicles or in the interfollicular
zones.
α
4.2.4.2
Nasal-Associated Lymphoid Tissue
In humans, inducible nasal-associated lymphoid tissue (iNALT) is a structure
distinct from the pharyngeal lymphoid ring
12
with pharyngeal (adenoids when
infected), palatine, lingual, and tubal (where Eustachian tube opens in the nasophar-
ynx) tonsils. This tissue is disseminated in the nasal mucosa. It belongs to the set
of mucosa-associated lymphoid tissue (MALT) with larynx- (LALT) and bronchus-
associated lymphoid tissue in the respiratory tract.
This organized lymphoid tissue in the nasal mucosa is characterizd by aggregates
of follicles in different parts of the nasal cavity that serve in local defense.
It contributes not only to the development of the local mucosal immunity, but
11
Four IgG categories exist in humans (IgG1-IgG4) with different amounts in blood (IgG1:
∼
66%, IgG2:
∼
23%, IgG3:
∼
7%, IgG4:
∼
4%). These IgG types can also be sorted according
to their as complement activator potency (IgG4
<
IgG2
<
IgG1
<
IgG3) and affinity to IgG Fc
receptors (Fc
γ
<
∼
R) on phagocytic cells (IgG2
IgG4
IgG3
IgG1) [
325
]. Phagocytic effector
γ
γ
γ
cells express 2 types of phagocytic Fc
receptors: high-affinity Fc
R1 and low-affinity Fc
R3.
Hetero-oligomers arise from connection of ligand-binding
α
chains to the common
γ
chain that is
required for the assembly of both Fc
R3 as well as triggering of phagocytosis. In mice,
IgG2a, IgG2b, and IgG3 subtypes, but not IgG1, efficiently activate complement. The affinity of
IgG to Fc
γ
R1 and Fc
γ
receptors on phagocytic cells depends on the antibody type, in addition to its category
(for a high-affinity antibody, IgG2a
γ
=
IgG2b
>
IgG3
>
IgG1, whereas for a low-affinity antibody,
IgG2a
IgG3) [
325
].
12
A.k.a. Waldeyer's tonsillar ring and Waldeyer's-Pirogov ring.
>
IgG1
>
IgG2b
>
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