GI infection and immunology

Question 1

massive antigen load

Answer 1

resident microbiota, dietary antigens, exposure to pathogens

Question 2

restrained activation

Answer 2

tolerance (food antigens; microbiota required for healthy imune system) vs active immune response (dual immunological role)

Question 3

function of microbiota

Answer 3

depends on nutrients available to increase cell numbers; peristalsis, contrations, defecations and digestive factors reduce amount

Question 4

dysbiosis of microbiota

Answer 4

symbionts (regulation), commensals, pathobionts (inflammation); can be unbalanced

Question 5

causes and disease development

Answer 5

infection and inflammation, genetics, hygeine, xenobiotics, diet

Question 6

dysbiosis

Answer 6

produce metabolites and toxins which can affect many tissues (brain, lung, liver, adipose, intestine) or whole body (systemic)

Question 7

physical barriers

Answer 7

epithelial (goblet cells - tight junctions - paneth cells), peristalsis, enzymes, low pH

Question 8

commensal bacteria

Answer 8

ecological niche

Question 9

immunological following invasion

Answer 9

MALT, GALT

Question 10

MALT

Answer 10

organised beneath epithelium as lymphoid mass containing follicles surrounded by HEV postcapillary venules (allow easy passage of lymphocytes); oral cavity rich in immunological tissue

Question 11

GALT

Answer 11

adaptive and innate immune response; sections of unorganised and organised

Question 12

non-organised GALT

Answer 12

intra-epithelial lymphocytes (T cells, NK cells); lamina propria lymphocytes

Question 13

organised GALT

Answer 13

Peyer’s patches (small intestine), caecal patches (large intestine), isolated lymphoid follicles, mesenteric lymph nodes (encapsulated)

Question 14

Peyer’s patches

Answer 14

immune sensors; found mainly distal ileum; aggregated lymphoid follicles covered with follicle associated epithelium (no microvilli, goblet cells, secretory IgA)

Question 15

Peyer’s patches

Answer 15

organised collection of naive T and B cells, requiring exposure to bacterial microbiota to develop; M cells sample antigens in gut lumen (FAE) and uptake antigens to Peyer’s patch lymphocytes

Question 16

M cells

Answer 16

express IgA receptors, facilitating transfer of IgA-bacteria complex into Peyer’s patches

Question 17

trans-epithelial dendritic cells

Answer 17

perform antigen sampling from submucosa through thin extensions through tight junction proteins in mucosal epithelial cells without compromising epithelial barrier

Question 18

B cell adaptive response

Answer 18

thymus-dependent B cell maturation

Question 19

mature naive B cells express IgM in Peyer’s patches, but switch to IgA upon antigen presentation

Answer 19

T cells and epithelial cells influence B cell maturation via cytokine production, then further mature to become SIgA and populate lamina propria

Question 20

SIgA formation

Answer 20

dimeric IgA in blood, poly-Ig receptor on epithelial cells, becomes SIgA (by neutralisation)

Question 21

large intesine

Answer 21

not as deep crypts; outer and inner mucous layer (outer so thick pathogen can’t enter)

Question 22

lymphocyte homing and circulation

Answer 22

activated lymphocytes to mesenteric lymph node (proliferation) to thoracic duct and circulation; either back to lamina propria (most) or other lymphoid organs

Question 23

entering lamina propria

Answer 23

integrin/MAdCAM-1 adhesion (homing) - strong binding leads to activation and arrest

Question 24

vaccine cholera

Answer 24

dukoral, oral, inactivated

Question 25

causes of infectious diarrhoea

Answer 25

viral, bacterial, protozoal parasitic

Question 26

viral infectious diarrhoea

Answer 26

rotavirus: (RNA, A most common), oral rehydration, vaccine (rotarix); norovirus (norwalk virus): RNA, sample PCR, acute gastroenteritis, faecal-oral

Question 27

bacterial infectious diarrhoea

Answer 27

campylobacter (curved): undercooked meat, untreated water, low infective dose can cause disease, no treatment normally required but can use antibiotics (azithromycin); E. coli: 6 pathogenic strains; cholera like toxin with watery diarrhoea; cause haemolyric uraemia syndrome (bloody diarrhoea); shigella like illness; C. difficile: antibiotics cause dysbiosis (disbalance) and cause C. difficile to propogate and cause bloody diarrhoea; isolate patient, stop current antibiotics, replace with others, if becomes increasingly difficult to treat use faecal microbiota transplantation