Lymph Drainage - Tissue Functioning and Remodeling in the Circulatory and Ventilatory Systems - page 181

Lymphoid neogenesis is defined by cellular assemblies during chronic
inflammation in any region of the human body. These tertiary lymphoid organs have
structural similarity to lymph nodes. Hence they are able to carry out angiogenesis
and lymphangiogenesis.

4.2.4 Tertiary Lymphoid Tissue - Mucosa-Associated

Lymphoid Tissues

4.2.4.1 Bronchus-Associated Lymphoid Tissue

Bronchus-associated lymphoid tissues (BALT) are ectopic organized structure with
B- and T-lymphocyte regions supported by specialized vascular networks, high
endothelial venules in the T-cell zone, and an overlying lymphoepithelium that
contains cells similar to microfold cells of Peyer's patches [ 324 ].
Bronchus-associated lymphoid tissues reside, in general, along bifurcations of
large bronchi and between an artery and bronchus. However, BALTs do not always
possess an overlying epithelium. Furthermore, BALTs are not always associated
with a bronchus and can form in the lung parenchyma.
Inducible bronchus-associated lymphoid tissue yields a niche for T-cell priming
and B-cell learning to assist in the clearance of respiratory pathogens. Non-classical
BALT that lacks contact with the epithelium is observed in most smokers (84%),
but also a small fraction of non-smokers (14%) [ 324 ].
Bronchus-associated lymphoid tissue pertains to the integrated mucosal system
that includes the gut-associated and nasal-associated lymphoid tissue (NALT),
among others. The development of this tertiary lymphoid tissue commences postna-
tally. Formation of BALT results from various diseases characterized by chronic
inflammation, infection, or autoimmunity, hence its preferred name of inducible
BA LT ( i BA LT ) .
Many of the molecular and cellular factors necessary for the genesis of secondary
lymphoid organs intervene during the formation of tertiary lymphoid tissue. How-
ever, classical factors of secondary lymphoid organogenesis, such as TNFSF2 and
chemokines CCL19, CCL21, and CXCL13 are dispensable for iBALT formation,
even though they influence its organization and function [ 324 ].
Some cell populations may participate in the BALT genesis rather than lymphoid
tissue-inducer cells, such as mature CD3

+ ,CD4 + and TNFSF14 + T lymphocytes

and TNFSF2-TNFSF3 2 + B lymphocytes. In addition, dendritic cells that, once

activated, interact with stromal cells are required to form, organize, and sustain
iBALT tissue. Integrin- α X + (CD11c + ) conventional and complement component

receptor CR2 ) follicular dendritic cells reside in T- and B-cell regions of

BALT and within B-cell follicles, respectively. Dendritic cells synthesize CCL19,
CCL21, CXCL12, and CXCL13, thereby fostering entrance and survival of lym-
phocytes within iBALT [ 324 ]. Moreover, activated plasmacytoid dendritic cells that
can produce high concentrations of TNF

+ (CD21 +

α and IL8 accumulate in lymphoid follicles

of COPD patients.