Gut-Associated Lymphoid Tissue - GALT
Small accumulations of lymphocytes or solitary
lymph follicles are found scattered in beneath the epithelium throughout the
gastrointestinal tract. However, the most prominent accumulations occur in the
ileum and appendix in the form of Peyer's patches. In the ileum, they form
dome-shaped protrusions into the lumen. Beneath the epithelial lining of the
domes, Peyer's patches extend from the lamina propria to the submucosa. Within
Peyer's patches, lymph follicles with germinal centers are typically located
deep in the submucosa.
The epithelium in contact with the lymphoid tissue
is specialised to facilitate the contact of antigens with cells of the immune
system. The epithelium appears columnar and contains cells with deeply
invaginated basal surfaces - microfold cells or M-cells.
Immune system cells can enter these invaginations (intraepithelial pockets)
where they are exposed to materials which have been endocytosed by the
epithelial cells and then released into the invaginations. Goblet cells are
rare or absent in the epithelium which covers the domes.
slides of appendix, ileum or Peyer's patches - H&E
Slides of the appendix and ileum may be useful is there
is no specially prepared slide of Peyer's patches. Extensive areas of lymphoid
tissue are alway present in the appendix, but domes and specialised sections of
epithelium may not. If you have a slide of the ileum hold it against the light
and see if parts of the wall look darker than the rest. These parts are likely
to contain lymphoid tissue and may show domes and/or specialised sections of
epithelium.
Peyer's Patch, Ileum - H&E
If you hold the sections against a light surface the areas which are occupied
by the lymphoid tissue should be readily visible - in H&E stained sections
they appear darker than the remaining tissue. Look at these areas under the
microscope. Identify the domes and their epithelial covering. The epithelium
will be lower than the epithelium covering the villi and goblet cells are rare
or absent. See if you can find intraepithelial pockets containing immune cells.
Even if no clear pockets are present, some lymphocytes should appear scattered
"over" the epithelium. In reality they will be located in the
intraepithelial pockets. High-endothelial venules should be present in the
lymphoid tissue beneath the domes but may be difficult to find. Next go further
towards the submucosa and see if you can find lymph follicles.
Draw the epithelium covering the domes at high magnification.
Include a scetch of the normal intestinal epithelium for comparison. Scetch the
appearance of Peyer's patches at low magnification.
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Title:
Gut-Associated Lymphoid Tissue - GALT
by:
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at
2013-02-15T03:30:00+07:00
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Gut-Associated Lymphoid Tissue - GALT