Lymph Drainage - Tissue Functioning and Remodeling in the Circulatory and Ventilatory Systems - page 185

(afferent L) L

capsule
subcapsular sinus

lymph node

A

medullary sinuses

V

L

(efferent L)

(afferent L)

L

cortical follicles

Fig. 4.1 Lymph node (A: artery; L: lymph vessel; V: veinule)

Lymph nodes contain lymphatic vessels and venules. Afferent lymphatics enter
a lymph node at several sites to fill the subcapsular sinus. The subcapsular sinus
drains into trabecular and cortical sinuses, then into the medullary sinuses, from
which lymph flows into the efferent lymph vessel.
Lymphocytes B and T circulate inside the lymph node via venules. They can
cross the endothelium and enter the lymph node. Afterward, B cells migrate to the
cortex and medulla, whereas T cells move to the paracortex. Otherwise, they exit
via efferent lymphatics.
Follicular dendritic cells and dendritic cells are antigen presenting. Dendritic
cells present antigens in the context of major histocompatibility complex class-1
and -2 molecules to stimulate T cells. Follicular dendritic cells target B cells with
antigen-antibody complexes.
The recruitment of lymphocytes and dendritic cells in the lymph node is regulated
by lymphoid chemokines. Non-hematopoietic stromal cells form the scaffold of
architecture of secondary lymphoid organs by producing chemokines. The lymphoid
chemokine set is composed of 4 ligands — CCL19, CCL21, CXCL12, and CXCL13
— and 2 receptors — CCR7 and CXCR5. Chemokines CCL19 and CCL21 as
well as CCR7 receptor are expressed by stromal cells of T-cell region. Chemokine
CCL21 is produced by the endothelium of venules of the lymph node, as well
as of lymphatics of non-lymphoid tissues. Chemokine CXCL13 is synthesized by
follicular stromal cells.
Fibroblastic reticular cells not only constitutively produce chemokines, but also
constitute support structures for migrating T lymphocytes and dendritic cells and
distribute antigens throughout the parenchyma of secondary lymphoid organs.