Flashcards in EXAM #1: IMMUNOLOGY OF THE GI TRACT Deck (48)
What is the big difference between mucosal immunity and "normal" immunity?
*Length of time*
-->Mucosal immunity does NOT last very long
How long do mucosal antibody responses last?
Months to a year
(vs. serum antibodies that persist for decades/life)
What are effector cells?
Lymphocytes that are "primed" to preform function immediately on contact with antigen
What is tertiary lymphoid tissue?
Any place in the body that becomes infected by microorganisms
What kind of lympoid tissue is the gut considered?
What are the physical mechanisms that prevent infection of the GI tract?
1) Acidity of stomach
2) Peristoltic motility
3) Detergent action of bile
4) Mucus secretion
What is GALT?
Gut Associated Lymphoid Tissue
List the sites of GALT.
1) Peyer's patches
3) Lymphoid aggregates in appendix/ large intestine
4) Lymphoid cells in lamina propria
What is a Peyer's Patch?
Aggregates of lymphoid tissue found in the ileum of the small intestine
What types of immunity are generated by Peyer's Patches?
1) IgA antibodies
Describe the structure of a Peyer's Patch.
- M-cells within the membrane of microfolds
- B-cell rich follicle
- T-cell area
- Germinal center
Where are APCs located in the Peyer's Patch?
T-cell rich areas adjacent to the Germinal Center
What is the function of M-cells in Peyer's Patches?
1) Uptake of antigen by endocyotsis and phagocytosis
2) Presentation of antigen to APCs
****Note that M-cells are sites of infection*****
List the microorganisms that utilize M-cells for introduction into the body?
1) Shigella--gets in via M-cells and then uses actin rockets to infect
What are IELs?
Intraepithelial Lymphocytes i.e. between enterocytes in the epithelium
What type of lymphocytes are most IELs? What are the two subtypes of these cells?
1) Alpha-Beta subtype*
What is the function of CD8+ IEL cells?
Cell-mediated immunity against:
1) Viral antigens
2) Intracellular bacterial antigens
Where are CD4+ T-cells located in the gut wall?
vs. CD8+ T-cells in the epithelium
In addition to CD4+ T-cells, what other immune cells are in the lamina propria?
- Plasma cells
- Dendritic cells
- Mast cells
Describe the basic immune response in the gut that results in IgA production.
1) M-cells uptake antigen
2) APCs bind antigen
3) APCs stimulate T-helper cells
4) T-helper cells stimulate antigen specific B-cells
Once B-cells have been stimulated, outline the path that the cell will take to find the Lamina Propria.
1) Pre-plasma cells leave Peyer Patch via efferent lymphatic capillaries
2) Migrates via mesenteric lymph channels
3) Enter bloodstream via the thoracic duct
4) Go "home" to the Lamina Propria
What is the role of addressins in B-cell stimulation?
These are the "homing" mechanisms that tell B-cells to go back to the Lamina Propria
How do IgA secreting Plasma Cells get from the Lamina Propria to the gut lumen?
1) IgA binds "poly-immunoglobulin receptors" on basolateral side of enterocyte
2) Endocytosis and transport to apical side
3) Release of IgA dimer + secretory component
What is "secretory component?"
Part of the poly Ig receptor that facilitates endocytosis of the IgA secreting plasma cell
What is the function of secretory component?
Prevents the breakdown of IgA in the gut lumen by proteolytic enzymes
What is the major immunoglobulin in secretions?
What are the two subclasses of IgA?
- cleaved by bacterial IgA protease
- can fix complement via alternate pathway
IgA2= not susceptible to IgA protease
What is the difference between the structure of IgA in the serum vs. mucousal sites?
Mucosal= IgA dimer
What is the role of IgA in immunity?
1) Opsonization of small pathogens for phagocytosis
2) Anti-parasite immunity by facilitating eosinophil degranulation