Morphology of FDCs - Diagram
Lymphnode_diagram

This is an idealized diagram of the compartmentalization of lymph nodes.

It shows the capsule of the lymph node (LN) in green with its afferent lymphatics (AFF; on top) and its efferent lymphatics (EFF) at the hilus. The subcapsular sinus (SS) and medullary (MS) sinuses are in yellow and the peripheral cortex in pink with its lymphoid nodules (follicles). Each nodule contains a germinal center which can be divided into a light (L) and a dark (D) region based on staining with H&E. Most of the FDCs are located in the light region.

The green arrow labeled FDC network corresponds to the morphology below:

FDCfili_morph

The paracortex (or deep cortical units; DCU) are adjacent to the peripheral cortex and are shown in blue. The paracortex contains T cells (dark blue) and interdigitating cells (IDC; white). Post capillary venules (PCV), also termed high endothelial venules (HEV), run through the paracortex. For the vascular supply to the lymphoid nodules see the red arteriole (A) entering the node at the hilus and the dark blue venule (V) leaving the hilus. The medullary cords (MC; in purple) extend from the lymphoid nodules into the medullary sinuses. MCs are shown to contain plasma cells (PC) which are known to enter from the germinal centers. In parts of the sinuses brown macrophages (MO) are shown. These are found in all MS. Reticular cells crisscrossing all sinuses are not shown.
FDC1and2 FDC3and4
This series of scanning electron micrographs (Figs. 1-4), as suggested by kinetic and morphological evidence, is believed to represent a maturation series. In figure 1, the cell has numerous developing dendrites with large club-shaped ends. The club shaped end is typical of dendrite growth in neurons and apparently here also. In adition, there is a veil-like cell process on the left of the cell body (see arrow heads). This process with its surface irregularities is reminiscent of the ATC shown earlier crossing the floor of the subcapsular sinus:

temATC3

An ATC Migrating Through a Pore of the Lymph Node Subcapsular Sinus Floor

The FDC in Fig. 2 is one with long slender filiform or filament like dendrites. These dendrites still have a club-shaped end but smaller. Fig. 3 shows an FDC regarded intermediate between the filiform and beaded dendrite stage shown in Fig. 4a. Fig. 4b is an enlargement of the area indicated by the arrow heads in Fig.4a and show he morphology of some of the beads that will take part in the formation of ICCOSOMES (see Humoral immune response on the front page). This series of FDC morphology was reported in: [REF1] [REF2]

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