steele Flashcards
1
Q
describe the length of time of the mucosal immune response
A
FAR SHORTER
- mucosal antibody responses = months to a year
- serum antibodys = persist for decades
2
Q
physical mechanisms of defense in GI tract
A
- High acidity of stomach –> retards bacterial growth
- Peristaltic motility, detergent action of bile, secretion of mucus limits uncontrolled growth
3
Q
Gut-associated lymphoid tissue (GALT)
A
- GALT = mucosal inductive sites
- peyer’s patches, appendix, lymphoid aggregates in appendix and large intestine, lymphoid cells in lamina propria
- Peyers patch = important in promoting IgA production and CTL response
- peyer’s patches, appendix, lymphoid aggregates in appendix and large intestine, lymphoid cells in lamina propria
- Most GALT sites have distinct B cell follicles and T cell areas, with antigen presenting cells present
4
Q
Peyer’s patches
A
- Dome epithelium = M-cells with cell membrane microfolds
- M cells transfer antigens from gut lumen to lymphoid tissue
- PRESENT by APC’s to T helper cells
- M cells transfer antigens from gut lumen to lymphoid tissue
- T cell rich parafollicular areas and distinct B cell rich follicle
- Endocytosis or phagocytosis used to take up antigens from gut:
- M cells interact physically with underlying APC’s and activate T cells
5
Q
Intraepithelial lymphocytes (IEL)
A
- epithelial cells of the GI tract for the intestinal lumen:
- IEL;s are composed PRIMARILY of T LYMPHOCYTES
- lymphocytes are in epithelium –> exposed to mucosal antigens
- CN8+ IEL possess cytotoxic function –> cell-mediated immunity against viral + intracellular bacterial infections
6
Q
Immune system cells of the lamina propria
A
- cells in lamina propria composed mianly of CD4+ t cells
- vast numbers of B lymphocytes, plasma cells, macrophages, dendritic cells, eosinophils and mast cell
7
Q
Role of IgA
A
- major immunoglobulin in secretions (saliva, mcuus, sweat etc)
-
Prevents binding of microbes to epithelila and facilitates expulsion
- opsonizes small pathogens for pahgocytosis
- eosinophil degranualtion via the FcalphaR for anti-parasite immunity
- IgA from lamina propria can diffuse into extracellular tissue spaces, drain into lymphatic system and transported into blood stream
- from bloodstream –> excreted into the gut via the bile
- OBSTRUCTIvE JAUNDICE (don’t excrete bile) = Increase plasma IgA
8
Q
Immune response in the GI tract
A
- M cells take up antigen by endocytosis and phagocytosis
- antigen is transported accross teh M cell in vesicles and released at basal surface
- antigen is bound by dendritic cells, which activate T cells
- T cells enter Peyer’s patches from blood vessels and encounter antigen transported across M cell and become activated by dendritic cells
- Activated T cells drain via mesenteric lymph nodes to thoracic duct and return to the gut via bloodstream
- activated T cells target the lamina propria and intestinal epithelilium of the small intestine
9
Q
role of pre-plasma cells
A
Pre-plasma cells –> form plasma cells and secrete IgA
- IgA binds to poly-immunoglobulin receptors –> transported across the cell and delivered onto the mucosal surface
- IgA antibodies bind to microbes, preventing access to epithelium + promoting clearance
10
Q
Mast cells
A
- beneath epithelia exposed to environement
- normal immunity = IgE-mediated defense against parasties
- eliciting food-induced allergic reactions
- diarrhea, anaphylactic shock
11
Q
Oral tolerance
A
- immunization with antigen via the GI tract can induce systemic unresponsiveness
- prevents hypersensitivity reactions to ingested food proteins
- Dose of oral antigen
- High Dose –> clonal deletion of antigen-specific lymphocytes
- Low Dose –> clonal anergy (unresponsiveness) + regulatory T cells suppress immune responses
- regulatory T cells developed in GALT can migrate systemically
12
Q
SELECTIVE IgA deficeincy
A
- not typically assocaited with clinical problems SINCE mucosal transport of IgM can compensate for absence of IgA
- Assocaited iwth greater risk for autoimmune disorders
- due to absorption of intestinal macromolecules that mimi self antigens –> may stimulate autoimmune responses
13
Q
Food hypersensitivites
A
- Some reactions to food proteins are the result of IgE-mediated immediate hypersensitivity rxns:
- nausea, vomiting, abdominal pain, and skin rashes
- pharyngeal edema and bronchospasm may be seen
- some food hypersensitivites –> fatal anaphylactic rxns
- vasoactive amines (principally histamine) –> severe changes in vascular permeability –> massice protein-losing enteropathy and hypoalbuminemia
14
Q
Gluten-sensitive enteropathy
A
- Disease of SMALL INTESTINE –> malabsorption due to villous atrophy:
- celiac sprue and idiopathic sprue
- hypersensitivity to gliadin (family of proteins in wheat gluten)
- epithelial cell lining intact, but functions abnormally
- confined to small intestine -_> gliadin not broken down into a.a.
- B and T cell infiltrates present in the lesion
- anti-gliadin IgA may play role in pathogenesis, main mediator of damage appears to be T cells
15
Q
Ulcerative colitis
A
- Relatively superficial inflammation limited to the large bowel:
- Ulcer formation and loss of mucosal absorptive function
- If anti-inflammatory or immunosuppressive therapy not sufficient to control disease –> total colectomy:
- surgery definitive since disease doesn’t affect small intestine
