General Defense Mechanisms Associated with the Digestive System
Mary Gorton
Microbiology Research paper
Page 1
General defense mechanisms associated with the digestive system
The gastrointestinal tract is a lymphoid organ, and the lymphoid tissue within it is collectively referred to as the gut-associated lymphoid tissue or GALT. The number of lymphocytes in the GALT is roughly equivalent to those in the spleen, and, based on location, these cells are distributed in three basic populations:
1. Peyer's Patches: These are lymphoid follicles similar in many ways to lymph nodes, located in the mucosa and extending into the submucosa of the small intestine, especially the ileum. In adults, B-lymphocytes predominate in Peyer's patches. Smaller lymphoid nodules can be found throughout the intestinal tract.
2. Lamina propria lymphocytes: These are lymphocytes scattered in the lamina propria of the mucosa. A majority of these cells are IgA-secreting B cells.
3. Intraepithelial lymphocytes: These are lymphcytes that are positioned in the basolateral spaces between lumenal epithelial cells, beneath the tight junctions (they are "inside" the epithelium, but not inside epithelial cells as the name may incorrectly suggest).
Another important component of the GI immune system is the M or microfold cell.
Mary Gorton
Microbiology Research paper
Page 2
M cells are a specific cell type in the intestinal epithelium over lymphoid follicles that endocytose a variety of protein and peptide antigens. Instead of digesting these proteins, M cells transport them into the underlying tissue, where they are taken up by local dendritic cells and macrophages. Dendritic cells and macrophages that receive antigens from M cells present them to T cells in the GALT, leading ultimately to appearance of immunoglobulin A-secreting plasma cells in the mucosa. Dendritic cells below the epithelium can also sample lumenal antigens by pushing pseudopods between epithelial cells. The secretory IgA is transported through the epithelial cells into the
Microbiology Research paper
Page 1
General defense mechanisms associated with the digestive system
The gastrointestinal tract is a lymphoid organ, and the lymphoid tissue within it is collectively referred to as the gut-associated lymphoid tissue or GALT. The number of lymphocytes in the GALT is roughly equivalent to those in the spleen, and, based on location, these cells are distributed in three basic populations:
1. Peyer's Patches: These are lymphoid follicles similar in many ways to lymph nodes, located in the mucosa and extending into the submucosa of the small intestine, especially the ileum. In adults, B-lymphocytes predominate in Peyer's patches. Smaller lymphoid nodules can be found throughout the intestinal tract.
2. Lamina propria lymphocytes: These are lymphocytes scattered in the lamina propria of the mucosa. A majority of these cells are IgA-secreting B cells.
3. Intraepithelial lymphocytes: These are lymphcytes that are positioned in the basolateral spaces between lumenal epithelial cells, beneath the tight junctions (they are "inside" the epithelium, but not inside epithelial cells as the name may incorrectly suggest).
Another important component of the GI immune system is the M or microfold cell.
Mary Gorton
Microbiology Research paper
Page 2
M cells are a specific cell type in the intestinal epithelium over lymphoid follicles that endocytose a variety of protein and peptide antigens. Instead of digesting these proteins, M cells transport them into the underlying tissue, where they are taken up by local dendritic cells and macrophages. Dendritic cells and macrophages that receive antigens from M cells present them to T cells in the GALT, leading ultimately to appearance of immunoglobulin A-secreting plasma cells in the mucosa. Dendritic cells below the epithelium can also sample lumenal antigens by pushing pseudopods between epithelial cells. The secretory IgA is transported through the epithelial cells into the
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