Immunity in the GIT

Question 1

what are the two groups of pattern recognition receptors

Answer 1

cell surface - transmembrane and intracellular receptors

fluid phase soluble molecules

Question 2

each lymphocyte has a unique antigen receptor - what happens when it it triggered by an pathogen

Answer 2

undergoes clonal expansion

Question 3

what is the estimated range of antigenic variability

Answer 3

10^9

Question 4

how any genes in the human genome

Answer 4

30,000

Question 5

describe the mechanism of antigen presentation

Answer 5

antigens internalised
broken down to peptides
associate with MHC class 2 and brought to cell surface
recognition by T helper cells which are then activated
these produce cytokines needed by B cells, T cells etc

Question 6

what are the roles of these molecules 
B lymphocytes
CD8
CD4
suppressor T lymphocytes

Answer 6

develop potential to secret antibodies - humeral immunity
cytotoxic T lymphocytes - cellular immunity
helper T lymphocytes - secrete growth factors which control immune reponse - help B lymphocytes and T lymph
may damp down immune response

Question 7

why do we need gut immunity

Answer 7

major site for foreigns bodies
GIT diseases kill more than 2 mill every year
lack of effective mucosal vaccines vs pathogens

Question 8

what does the gut mucosal barrier encounter

Answer 8

harmless antigens such as food, normal flora, pathogenic organisms which try to colonise and invade - ie this is the first line of defence

Question 9

what are the two types of immune response we need in the gut

Answer 9

ignorance / tolerance from normal flora

protection from foreign matter

Question 10

what are the innate defences of the gut immune system

Answer 10

commons bacterial flora
epithelial barrier
biochemical faros produced by epithelial cells

Question 11

what are specific defences of the gut immune system

Answer 11

lymphoid tissue associated with mucosal surfaces

Question 12

what are m cells in the gut and what is their role

Answer 12

microfold cells
found in the follicle-associated epithelium of the Peyer’s patch; have the unique ability to sample Ag from the lumen of the small intestine and deliver it via transcytosis to APC and lymphocytes located in a unique pocket-like structure on their basolateral side.

Question 13

what is the approx number of bacteria in the gut and how many different species

Answer 13

10^14

300 - 1000

Question 14

describe how gut bacteria changes with age

Answer 14

infants acquire gut flora swallowed from breast milk or vaginal fluid at delivery

colonic microflora is adult like after 2 years of birth but don’t fully resemble until much older

elderly harbour fewer bifidobacteria and higher levels of enter-bacteria and clostridium difficile

Question 15

what is a prebiotic

Answer 15

non-digestible food ingredient that beneficially affects the host by selectively stimulating the growth and/or activity of one or a limited number of bacteria in the colon, and thus improves host health

Question 16

describe how inulin is a prebiotic

Answer 16

Inulin is indigestible by the human enzymes ptyalin and amylase, which are adapted to digest starch. As a result, inulin passes through much of the digestive system intact. It is only in the colon that bacteria metabolise inulin, releasing carbon dioxide, hydrogen and/or methane

Question 17

what are the benefits of gut microflora

Answer 17

resistance to colonisation by pathogens 
stimulate local immunity 
oral tolerance 
nutrition 
epithelial cell turnover 
intestinal motility

Question 18

what is symbiosis in the gut

Answer 18

in the absence of commensals a poor immune reposes develops and oral tolerance cannot be induced

Question 19

what percentage of faeces in weight does bacteria take up

Answer 19

60%

Question 20

what is the problem with antibiotic and protection in the gut

Answer 20

kill many commensal bacteria which allows pathogens to colonise and proliferate such as clostridium difficile

Question 21

what is eubiosis and dysbiosis

Answer 21

state of balance between microbial population

imbalance

Question 22

what is IBD

Answer 22

group of disorders inflammatory bowl disease

Question 23

what are the most common kind of IBD

Answer 23

crohns and ulcerative colitis

Question 24

describe the structure and function of the epithelial barrier

Answer 24

prevents penetration by microorganisms
single layer thick
self renewing from stems cells in crypts of leiberkhun

Question 25

what are the 4 types of cells the stem cells mature into in the gut

Answer 25

enterocytes
goblet cells
enteroendocrine
paneth cells

Question 26

what are the three defence mechanism of the epithelial barrier

Answer 26

goblet cells
enterocytes
secretory IgA

Question 27

what is the role of goblets cells

Answer 27

produce muffins to provide for mucus laters that resist microbial access

Question 28

what is the role of enterocytes

Answer 28

mechanical action, filial action creates current ro remove microbes that are poorly adhered
also produce defensins and acthelicidins
produce lysozyme and lactoferrin

Question 29

what is the role of secretory IgA

Answer 29

may be of limited specificity to bind to microbes

Question 30

what does the specific immune system of the gut require

Answer 30

transport of antigens through the epithelial barrier
co-operation between epthialial cells, APC’s - T and B lymphocytes
tolerance vs commensal microbial flora and food antigens
protective immunity vs pathogens

Question 31

what is the structure and function of organised mucosal associated lymphoid tissue (mucosal follicles)

Answer 31

aggregated follicles in peters patches (lower part of the small intestine)
singel follicles in along length of GI tract
induction of immune response

Question 32

what are diffuse mucosal associated comprising widespread leucocytes

Answer 32

intra epithelial lymphocytes (most of which are T cells)
leucocytes of the lamina propria
effector sites for immune responses

Question 33

describe the induction of specific immune response at a payers patch

Answer 33

M cells adapted to antigen uptake
pass antigens to professional APCs
dendritic cells preset antigens to T cells and B cells which are activated
B cells migrate to mesenteric lymph nodes
differetineated plasma cells migrate to tissues
plasma cells secrete IgA

Question 34

what does overwhelming response to antigen produce

Answer 34

oral tolerance

Question 35

describe the structure and function of intraepithelial lymphocytes

Answer 35

large granular lymphocytes 
mostly CD8 (cytotoxic T cells) 
produce IL2 IFN-y
cytotoxic ie perforin and granzyme 
role in immunosurveillance

Question 36

what are lamina propria lymphocytes and what is their role

Answer 36

found in loose connective tissue lying under the epithelium 
mostly CD4 (Helper T cell)

Question 37

what do these cells do
Th1
Th2
Th17

Answer 37

cell mediated responses - intracellular pathogens
antibody mediated responses (allergens, parasites)
Th17 cell mediated responses - mucosal pathogens, IBS

Question 38

what is the difference in production of IgA1-2

Answer 38

IgA exists as two isotypes, IgA1 (90%) and IgA2 (10%):
IgA1 is found in serum and made by bone marrow B cells
IgA2 is made by B cells in the mucosa
IgA2 : IgA1 ratio in the gut = 3:2

Question 39

where is IgA synthesised

Answer 39

by plasma cells in the lamina propria

Question 40

what are the properties of secretory IgA

Answer 40

relatively resistant to proteolysis
neutralises viruses and toxins
enhances non-specific defences mechanisms - lactoperoxidase and lactoferrin
inhibits bacterial adhesion
macromolecule absorption and inflammatory effects of other Ig’s

Question 41

what does lactoperoxidase do

Answer 41

antimicrobial agent in milk, saliva and tears that helps oxidation of toxic thiocyanate ions by hydrogen peroxide.

Question 42

what does lactoferrin do

Answer 42

in mucosal secretions inhibits both bacteria and viruses by binding to host cells/viral particles. This reduces the ability of bacteria and viruses to attach to cell membranes.