Immunology

Question 1

Gut Immune System

Answer 1

Specialised antigen uptake

• respond to pathogenic antigens
• don’t respond to unharmful antigens

Memory T cells predominate

Question 2

Peyer’s patch

Answer 2

Lymph node in the SI
Situated immediately underneath columnar epithelium
Antigenic material goes straight from lumen of gut to the peyer’s patch via “M” cells
Immune activation occurs

Question 3

M cells

Answer 3

Transport antigens from lumen -> peyer’s patch
Antigen then released in peyer’s patch

Massive surface area - absorb as much antigen as possible

Question 4

Dendritic cells

Answer 4

APC’s - capture antigen and present it to T cells and prepare for T cell activation
Can extend their dendrites across the epithelial layer to the lumen of the gut and directly sample antigens

Question 5

T cells

Answer 5

Become activated once they enter peyer’s patch (via blood) and are exposed to dendritic cells
Activated T cells exit peyer’s patch via lymphatic system and drains to mesenteric lymph nodes
T cells trafficked back to the gut

Question 6

MAd CAM-1

Answer 6

Present on endothelial surface of gut immune system

Question 7

Ig_ levels in the gut immune system

Answer 7

IgA (80%) - dimeric form
IgM (15%)
IgG (5%)
(this is essentially the reversal to the systemic Ig_ levels)

Question 8

IgA

Answer 8

Transfer IgA across epithelial cell into the lumen using ‘poly Ig receptor’
IgA released into lumen along with the secretory component (part of the poly Ig receptor) to protect it.
The IgA in the lumen binds to and neutralises pathogenic material.
Important in defence of the gut

Question 9

Intraepithelial lymphocytes

Answer 9

Mainly CD8+ T cells
contain full killing machinery
always ready to respond
found in epithelial lining of the gut

Question 10

Mucosal response to infection

Answer 10

We want a Th2 response as this produces antibodies (i.e.: IgE which activates mast cells and eosinophils)

Question 11

HIV (mechanism of action)

Answer 11

Dendritic cells take up harmful HIV (antigen) and present it to CD4+ T cells i
HIV is thus transferred from dendritic cell -> T cell
This spreads infection further
Activated T cells move back to gut and HIV kills the memory T cells in the gut

Question 12

Selective IgA deficiency

Answer 12

Common

Presentation: asymptomatic, recurrent sinopulmonary infections, coeliac disease

Question 13

CVID

Answer 13

Patient fails to make enough Ig
Mainly affects adults
Management: Ig replacement therapy

Question 14

XLA

Answer 14

X-linked (only affects males)
No B cells - therefore no antibodies
Age group: children (after 6 months)
Management: Ig replacement therapy

Question 15

SCID

Answer 15

Profound defect in T cells and B cells

Age group: children (first 3-6 months)