Immunology

Question 1

Physiological function of mucosa tissues (4)

Answer 1

Gas exchange
Food absorption
Sensory activity
Reproduction

Question 2

Lamina propria is filled with

Answer 2

Immune cells of all stages except neutrophils - Neutrophils only migrate to region during infection

Question 3

Isolated lymphoid follicles produces

Answer 3

B cells

Question 4

Peyer’s patches structure (3)

Answer 4

Covered by epithelial cells 
Contains M (Microvilli) cells with specialized membrane ruffles - Increases SA for absorption
Underneath dome has dendritic cells, germinal centres and T cell centres

Question 5

Immune action of M cells (3)

Answer 5

M cells take up antigen by endocytosis and phagocytosis
Antigen is transported across M cell in vesicles and released at basal surface
Antigen is bound by dendritic cells which activates T cells

Question 6

Dendritic cells and epithelium layer

Answer 6

Can extend processes across epithelial layer to capture antigen from gut lumen

Question 7

Integrin of mucosa epithelium

Answer 7

Alpha 4: Beta 7 integrin

Question 8

T cell immune action (4)

Answer 8

Enters Peyer’s patches from blood vessels directed by receptors CCR7 and L-selectin
T cells encounter antigen transported across M cells and are activated by dendritic cells
Activated T cells drain to thoracic duct via lymph nodes and return to gut via bloodstream
Activated T cell expressing Alpha 4: Beta 7 integrin and CCR9 home to lamina propria and intestinal epithelium

Question 9

Humoral Intestinal response ratios (4)

Answer 9

IgA - 80%
IgM - 15%
IgG - 5%
Systemic is opposite (GMA of same ratio)

Question 10

IgA secretion (3)

Answer 10

IgA binds to poly-Ig receptor on basolateral face
Endocytosis and transcytosis to apical face
IgA dimer is released with secretory component - Broken down quickly with secretory component

Question 11

IgA functions (3)

Answer 11

Neutralises pathogens and toxins on gut surface
Neutralises antigens internalized in endosomes
Exports toxins and pathogens from lamina propria

Question 12

Intraepithelial lymphocytes - Special T cells (6)

Answer 12

90% of T cells with 80% CD8+
Activated appearance with killing machinery
Restricted antigen receptor repertoire
Expression of Alpha E: Beta 7 integrin anchors them in epithelium
2 types with different recognition mechanisms
Immunopathology coeliac disease

Question 13

Intraepithelial lymphocyte (IEL) immune response (2)

Answer 13

Infection, toxins or damage causes secretion of gliadin peptide and displays CD8 IEL via MHC class 1
Activated IEL kills infected cell by perforin/granzyme and Fas-dependent pathways

Question 14

Mechanisms of mucosal hyporesponsiveness (4)

Answer 14

Commensal organisms help regulate local hyporesponsiveness- PPAR gamma activation
Anergy or deletion of antigen specific T cells- No co-stimulation
Generation of regulatory T cells particularly CD4+ TGF Beta producing TH3 cells - Weak co-stimulation
(Both immunosuppressive and induces switching of B cells to IgA production)

Question 15

Mucosal response to infection and regulation of mucosal immune responses (5)

Answer 15

Innate mechanisms eliminate most intestinal infections
Activation through pattern recognition receptors ligation
Intracellular sensors in epithelial cells, PRR, activate the NFkB pathway
Gene transcription and production of cytokines, chemokines and defensins
Activation of underlying immune response

Question 16

Outcome of infection by intestinal pathogens is determined by

Answer 16

Complex interplay between the microorganism and the host I.R.

Question 17

What happens when mucosal immunity becomes dysregulated in infectious disease (3)

Answer 17

Infection crosses mucosa and fuses to dendritic cells which shuttle virus to regional lymph nodes
Infection spreads to CD4+ lymphocytes
These viral infected cells go into bloodstream and disseminate across the body.

Question 18

Selective IgA deficiency (3)

Answer 18

Asymptomatic
Recurrent sinopulmonary infections
Increases Coliac disease risk by 10 times

Question 19

Common Variable Immuno-Deficiency (CVID) (3)

Answer 19

Recurrent sinopulmonary and GI infections
Failure to differentiate into Ig secreting cells
Low IgG,A,M,E

Question 20

X-linked Agammaglobulinaemia (XLA) (2)

Answer 20

Sinopulmonary and GI infections with devastating systemic manifestations of chronic enteroviral infections
No B cells

Question 21

Chronic Granulomatous Disease (CGD) (2)

Answer 21

Staph. aureus/Inflammatory granulamos-pneumonia, liver abscess, perianal abscess and skin abscess
Failure of phagocyte respiratory burst

Question 22

SCID (3)

Answer 22

Profound defect in T and B cell immunity
Causes oral candidiasis, Chronic diarrhoea, Interstitial pneumonitis
Pathogens commonly involved are EBV and rotavirus

Question 23

Food allergy (3)

Answer 23

Type I hypersensitivity
IgE secreted by plasma cells forms crosslink on mast cell surface
This secretes signals to B cells triggering more IgE production
Memory response- immune system must be primed

Question 24

Coeliac Disease/ Gluten sensitive enteropathy (6)

Answer 24

Genetic disease to HLADQ2/HLADQ8 (MHC class 2 molecules)
NOT an allergy
Trigger is enteric viruses
Gamma interferon from Gluten specific T cell activate epithelial cells which produce IL-15 inducing proliferation and activation of IEL
Diagnosed by biopsy (GOLD STANDARD) and serology (looks for IgA auto antibodies with 95% clinical sensitivity)
Gluten must be consumed prior to testing for antibodies to be present

Question 25

Crohn’s disease (5)

Answer 25

Effect all GI Tract - Commonly in distal ileum and colon
Gene identified is NOD2 - 10 to 15% of cases
Focal and discontinuous inflammation with deep fissures with or without granulomas
Mediated by TH1 CD4+ T cells, gamma interferon, IL-12, TNF alpha
Inappropriate immune response to commensal bacteria

Question 26

Ulcerative colitis (7)

Answer 26

Prevalence increase in children of immigrants
Only in colon and rectum (starts at rectum)
Develops arthritis, uveitis and skin lesions
Distortion of the crypts with infiltration of monocytes, neutrophils and plasma cells
Inflammation and ulceration just in surface mucosa
May be an NK T cell mediated disease via IL-13
Treatments are NSAIDS and immunosupressive drugs and anti-TNF alpha