W13L22 - Immune Response to Infectious Diseases

Question 1

Immunity to Fungi

Answer 1

Depends on identity
- virulence factors
- physiological traits
- nutritional requirements
Immunosuppression is most important predisposing patient factor
Innate
- phagocytosis
- neutrophils 
- macrophages
Acquired
- cell mediated immunity 
- extracellular fungi - Th17 response
- intracellular fungi - macrophage response with Th1

Question 2

IR to Fungi - Cytokine Release

Answer 2

Both innate and adaptive IR to gundi results in cytokine release
IL-17 recruits neutrophils
Both IL-17 and Il-22 stimulates release of antimicrobial peptides

Question 3

Immune Response to Viruses

Answer 3

Innate and adaptive responses to viruses aimed at blocking virus entry to cells and eliminating infected cells

Question 4

Immune Response to Viruses - Innate Immunity

Answer 4

Inhibition of infection by type 1 interferons

• type 1 IFNs produced by virally infected cells
• they cause sequestration of lymphocytes to lymph nodes
• increase cytotoxicity of NJ cells
• type 1 IFNs can prime nearby uninfected cells as well as being self acting on an infected cell
• can stimulate internal mechanisms for inhibiting progression of viral infection in uninfected cells

Question 5

Internal Mechanisms of Type 1 IFN

Answer 5

1. Inhibit viral protein synthesis in infected cells
2. Stimulates production of enzymes which can degrade viral RNA
3. Can inhibit viral gene expression and viron assembly

Question 6

Mechanisms for Removing Tumor/Virus Cells

Answer 6

1. NK cells (innate IR) kill by detecting lack of MHC class 1 on cell surface
2. NK cells (adaptive) kill by detecting antibody bound to a cell
3. Cytotoxic (adaptive) T cells kill by detecting antigen presented on MHC 1

Question 7

Immune Response to Viruses - Adaptive Immunity

Answer 7

Type 1 IFNs
- increase cytotoxicity of CD8+ cytotoxic lymphocytes
- promotes differentiation of naive T cells into Th1 cells
- up regulates expression of class 1 MHC molecules on the surface of infected cells
Killing of infected cells by CD8+ cytotoxic lymphocytes
Antibody dependent cell mediated cytotoxicity
Neutralisation of virus particles by antibody

Question 8

Virus Adaptive Immunity - CD8+ Cytotoxic Lymphocytes

Answer 8

APCs phagocytose viral infected host cells
APCs present viral antigens to primed Th1 cells and naive cytotoxic T cells
Th1 cells release IFNγ and IL2
Cytotoxic T cells become primed to recognise virally infected cells

Question 9

Virus Adaptive Immunity - Antibody Dependent Cell-Mediated Cytotoxicity

Answer 9

NK cells detect antibody coated cells via Fc receptors
Mechanism for removal of tumor cells and virally infected cells
Antibody isotope only IgG (Th1)

Question 10

Virus Adaptive Immunity - Neutralisation of Viruses by Abs

Answer 10

Abs bind to surface antigens of a virus particle
Blocks adhesion of virus to mucosal epithelium/cell membrane
Antibody isotopes - IgG1 and 3 (Th1), IgA (Th2), IgM (still adaptive but no Th1 or 2 required)
Then targeted by NK cells and phagocytes

Question 11

Why can viruses still cause illness?

Answer 11

Antigenic variation
Inhbition of presentation of MHC class 1 
IL1 normally promotes inflammation
IFNγ normally promotes:
- Th1 differentiation
- B cell isotope switching to IgG
- activation of macrophages (Th1)
- increased expression of class 1 and 2 MHC
IL10 inhibits IL12

Question 12

Antigenic Shift and Antigenic Drift

Answer 12

Antigenic shift 
- genetic re-assortment of genes
- creates new viruses
- antigenically distinct precursors
Antigenic Drift
- mechanism of variation in viruses by mutation
- accumulation of mutations in genes that encode for surface antigens
- occurs in influenza A

Question 13

Immune Response to Parasites

Answer 13

Innate
- phagocytosis by macrophages/neutrophils
- many protozoa can survive inside phagocytes
Adaptive
- protozoa: Th1 assisted phagocytosis (IFNγ) and CD8 cytotoxic T cells
- helminths: Th2 and IgE leading to activated eosinophils