Lymph Drainage - Tissue Functioning and Remodeling in the Circulatory and Ventilatory Systems - page 184

produced by follicular dendritic cells is a B-cell chemoattractant that serves to
regulate the compartmentation of CXCR5 B lymphocytes within the follicle.

It also recruits lymphoid tissue-inducer cells and follicular helper T lymphocytes.
Stromal cells are the major producers of CCL21 in NALT.

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4.2.5 Lymph Nodes

Lymph nodes (few mm-2 cm) filter the lymph and serve as phagocytosis sites
of toxins and microorganisms. In addition, they are maturation loci for some
lymphocytes and monocytes. Lymphatic vessels process the lymph in lymph nodes
via dendritic cells.

4.2.5.1 Lymph Node Formation

Connective tissue protrudes into lymph sacs to form precursor structures of lymph
nodes. Mesenchymal cells differentiate into specific lymph node organizer cells.
Each set of lymph nodes (cervical, thoracic, mesenteric, etc.) develops according to
a combination of various regulators.
Establishment of lymph nodes relies on interactions between TNFRSF3

+

organizing cells 15

and TNFSF2-TNFSF3 2 + ,CD3 − ,CD4 + ,PTPRc + inducer

cells B classical and non-

canonical pathways (Vol. 4 - Chap. 10. Other Major Signaling Mediators)
that initiate the production of adhesion molecules and chemokines to recruit
circulating cells. In addition, receptor-activator of NF

[ 319 ]. This cooperation primes 2 sequential NF κ

B ligand TNFSF11 and
its receptors TNFRSF11a and TNFRSF11b are essential regulators of lymph node
organogenesis, among other functions.

κ

Lymph Node Structure

Lymph nodes are surrounded by a fibrous capsule and an underlying subcapsular
sinus (Fig. 4.1 ). The inner region of lymph nodes can be decomposed into 3 parts:
cortex, paracortex, and medulla. Elastin and reticular fibers form a supporting
network within lymph nodes that delimit follicles of packed leukocytes in the cortex.
Primary cortical follicles are clusters of B lymphocytes and follicular dendritic
cells. After antigen stimulation, B cells undergo intense proliferation and give rise
to secondary follicles, the so-called germinal centers .The paracortex is composed
of T lymphocytes and dendritic cells. The medulla consists of medullary cords
separated by lymph-filled medullary sinuses. Medullary sinuses contain histiocytes
(immobile macrophages) and reticular cells.

15 I.e., lymphotoxin- β receptor-expressing cells.