Extracellular Immunity

Question 1

Why are parasites a difficult challenge to the immune system?

Answer 1

Most are extracellular and too big for phagocytosis
Thick coats- not penetrated by complement of T cell perforin
Molecular mimicry
Anatomical seclusion
Surface antigen shedding
Interference with antigen presentation
Immunosuppression
Migration

Question 2

What are the physiological changes induced in the GI tract for anti-worm immunity and what do they prevent?

Answer 2

Increases the number of goblet cells- increases mucin secretion, increased intestinal mobility, water influx into the intestinal lumen
Makes GI inhospitable for the parasite

Question 3

What is a helminth infection?

Answer 3

An infection by parasites

Question 4

What are they responses of helminth infections and what cytokine drives it?

Answer 4

TH2 cell response driven by IL-4:
TH2 activate macrophages and activate eosinophils and mast cells
TH2 cells promote a strong antibody response based on neutralising IgG an IgE

Question 5

What do mast cells do in response to helminth reactions

Answer 5

Surface of mast cells are loaded with IgE and antigen binding causes degranulation and release of pharmacological agents, resulting inflammation can be detrimental to worms as it stimulates mucin secretion and gut mobility

Question 6

How do eosinophils and mast cell cause parasite immunity?

Answer 6

Both eosinophils and mast cells react to antigen-complexed IgE and release vasoactive molecules with potent anti-worm activities:
Mast cells stimulate expulsion via mucus
Goblet cells and IgA do thin in ruminants
Eosinophils kill worms

Question 7

What are the 4 ways antibodies control extracellular infections?

Answer 7

Direct damage or complement mediated lysis
Prevents spread by neutralising attachment site- prevents escape from lysosomal vacuole, and inhibition of lysosomal function
Enhancement of phagocytosis
Antibody dependent cell mediated cytotoxicity

Question 8

How do TH2 cells promote neutralising antibodies?

Answer 8

Driven by IL-4
TH2 supresses activation of macrophages
Promore a strong antibody response based on neutralising IgGs
Most effective to combat extracellular pathogens

Question 9

How do antibodies protect against extracellular bacteria?

Answer 9

Neutralise toxins
Kill bacteria
Opsonize bacteria
Intracellular killing by macrophages