Immunology Flashcards
what do goblet cells produce?
mucus
what do paneth cells produce?
defensins
what is the function of peyers patches?
antigen sampling and immune activation
compare small intestine and large intestine in terms of crypts and villi?
small intestine has both villi and crypts
large intestine has only crypts- no villi
compare goblet cells in the small intestine and large intestine?
more goblet cells in large intestine than small intestine
where are paneth cells found?
small intestine (none in large intestine)
where are peyers patches found?
lamina propria of small intestine
none in large intestine
what type of cells do peyers patches contain?
macrophages dendritic cells intra-epithelial lymphocytes effector T cells IgA secreting plasma cels innate lymphoid cells stromal cells (eg fibroblasts)
apart from in peyers patches, how else can antigen presentation in the gut occur?
directly across epithelium
what immune cells extend across the epithelial layer to capture antigens?
dendritic cells
what are peyers patches covered with?
an epithelial layer containing M cells
what is the function of M cells?
M cells sieve antigens through into peyers patches
how do M cells take up antigen?
via endocytocis and phagocytosis
what happens if a dendritic cell within a peyers patch or directly across the epithelium takes up an antigen while in the right pro-inflammaroty state?
the dendritic cell will migrate to the mesenteric lymph nodes to present the antigen and stimulate acquired immune response
what is the most common antigen type in the gut?
IgA
how are circulating T cells directed to Peyers patches from the blood vessels?
CCR7 and L-selectin are homing receptors which direct the T cells
once a T cell has become activated by dendritic cells from peyers patches what integrin and chemokine become expressed?
a4b7 and CCR9
what do a4b7 and CCR9 allow the T cell to do?
home to the lamina propria and intestinal epithelium of the small intestine
what is the function of chemokine CCR7?
allows T cells to keep recirculating
what happens to CCR7 when a T cell has become activated?
CCR7 is no longer expressed
what adhesion molecule on the endothelium does the a4b7 on the activated T cell bind to?
MAdCAM-1
what chemokine is specific to the small intestine and attracts the CCR9 on the activated T cell?
CCL25
when might IgG be the most abundant antibody in the gut?
flare of ulcerative colitis
compare immunoglobulin structure in the circulation to structure in the gut?
dimeric in the gut
monomeric in circulation
in a dimeric immunoglobulin what joins the 2 immunoglobulins together?
J chain
joining chain
why does IgA coat the lumen of the cut?
creates an immune barrier
why must immunoglobulins keep being produced for the immune barrier to maintain?
because IgA is constantly lost from the barrier during gut contractions and absorption of food
what is the function of the poly-Ig receptor?
binds to the IgA dimer and facilitates endocytosis across the basal membrane
what happens when the IgA dimer-poly-Ig-receptor complex gets to the lumenal membrane?
the poly-Ig receptor is cleaved but a remnant (secretory piece) still remains on the IgA which goes into the lumen
what is the function of the secretory piece that is bound to the IgA in the lumen of the GI tract?
prevents IgA being digested
remember immunoglobuls are proteins
what are intraepithelial lymphocytes?
pre-activated lymphocytes (mainly cytotoxic)
what is the importance of mucosal hyporesponsiveness?
so the immune system isn’t attacking every antigen (most non-pathogenic) found in the gut lumen
what is anergy of specific T cells?
switching off of specific T cells (ie specific to non pathogenic antigen) so they will not attack cell
what 2 factors cause anergy of T cells?
high TGFbeta (transforming growth factor beta) and low pro-inflammatory cytokines
what microscopic changes causes scalloping of the small intestine seen in coeliacs disease?
villous atrophy
total loss of villi
what is the gold standard for diagnosis of coeliacs?
biopsy
what serology test is a very useful screening test fo coeliacs disease?
serology for IgA anti-TTG
anti-tissue transglutaminase auto antibodies
when might you get a false negative on serology testing for coeliacs disease?
IgA deficiency
patient hasn’t eaten gluten
what is the main cause of persistent symptoms of Coeliacs disease?
lack of compliance
compare the parts of the GI tract that ulcerative colitis and crohns affect?
UC- colon (rectum+proximally)
Crohns- any part with skip lesions
compare the depth of inflammation of the GI tract that ulcerative colitis and crohns affect?
UC- mucosal
Crohns- transmural/granulomatous
which has a greater genetic link- crohns or UC?
crohns
compare the types of CD4 T cells involed in crohns and UC?
UC- Th2
Crohns- Th1
what type of hypersensitivity reaction is a food allergy?
type 1 hypersensitivity
what is the usual hypersensitivity response to food?
vomiting diarrhoea pruitis urticaria anaphylaxis (rarely)
