Antigen Transport by ATCs
AG_Transport

LEGEND:
VC: veiled cell (an ATC);
ATC: Antigen Transporting Cell;
Ag: Ag-Ab-C';
SS: subcapsular sinus of lymph node;
L: lymphocyte;
MF: macrophage;
FB: follicular B cell;
Red Arrows: indicate direction of Ag transport.

ANTIGEN TRANSPORT BY ATCs:


The figure above illustrates active transport of antigen (Ag) in the form of immune complexes (black) by a group of cells of varying dendritic morphology (green cells). Based on their antigen transporting role, these cells are termed Ag-transporting cells (ATCs). This concept of Ag transport is based on a combined light and electron microscopic study [REF].
Following injection of the histochemically detectable antigen, horseradish peroxidase (HRP) into immune mice, the draining lymph nodes were examined at successive times for Ag transport. ATCs were recognized in lymph nodes in this study for the first time. This study helped to determine whether Ag flows to follicles via the lymph or whether it is actively transported by cells. The results showed that Ag is trapped initially on the surface of veiled cells (VC) which migrate through pores in the floor of the subcapsular sinus (SS) [see red arrows] into the cortex of lymph nodes and then to lymphoid nodules (or follicles; light-blue background). Along the way, these ATCs appear to mature into FDCs. This observation prompted subsequent work on the possible bone marrow derivation of FDC precursors and received support from the apparent identity of ATC and FDC phenotype [REF] and the presence of donor phenotype FDCs in SCID mouse recipients [REF].

ELECTRON MICROGRAPHS (EM):
1. The EM of the veiled-like cell (VC) in the SS, shows the cell with the black, deposit of the antigen-Ab (HRP-anti-HRP) complexes on the surface of its veils (arrows). Some of the veils are flattened against the cell body (arrow-heads).
2. The EM of the ATC shows a cell in transit through a pore of the floor of the SS. Note that the body of the cell is already through the pore (arrows) and lies beneath the basement membrane of the SS (arrow-heads). The immune complex coated processes of this cell are still in the SS.
3. The EM of the FDC is shown illustrating the development of the antigen transport pathway. (See legend to the right of the EM).

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