Lecture 29: Infection and immunity

Question 1

What factors affect infection and response to it?

Answer 1

• Environmental
• Social/epidemiological
• Psychological
• Genetic/lineage
• Ontogenetic/personal history
• Behavioural

Question 2

What are the lymphocyte effector populations?

Answer 2

• B Antibody production (B-lymph)
• Antigen-specific cytotoxicity (CD8 T cells)
• Natural killer activity (NK lymphocytes)
• ADCC (K lymphocytes)

NK & K are functions of same subsets of cells. Manifest one or other depending on context of antigen presentation

Question 3

What are the lymphocyte regulator cells?

Answer 3

• Cytokine production (CD4 T lymph)
• TH1 (Intracellular)
• TH2 (Multi-cellular i.e parasites, allergens)
• Treg (Regulatory T cells, down regulation)
• TH17 (Mucosa and inflammation)

Question 4

Describe antibody responses change between primary and secondary response:

Answer 4

Class switch from IgM to IgG controlled by T cells, needs CD40-CD40Ligand interaction

IgG much high conc. second time.

Question 5

What happens in hyper-IgM syndrome?

Answer 5

No CD40-CD40Ligand interaction = No class switching to IgA, IgG, IgE

Question 6

What are the microbial factors when it comes to infection:

Answer 6

• Type of organism
• Amount
• Route of entry i.e Gut->Peyers Patches, Blood->Spleen
• Virulence

Question 7

What are the host factors that influence infection?

Answer 7

• Integrity of the innate barriers
• Adaptive immune competence
• HLA, TCR and Ig genes
• Previous exposures
• Other infections

Question 8

What factors influence immunity and infection?

Answer 8

Microbial and host factors

Question 9

What can the lymphocyte populations be divided into?

Answer 9

Effectors and regulators

Question 10

Write some notes on viruses and its antigens:

Answer 10

• Lytic or integrated cycle
• Capsid antigens
• Internal structural components (HLA Class 1)
• Metabolic products (HLA Class 1)

Question 11

Write some notes on bacteria (and fungi) and its antigens:

Answer 11

• Extracellular (S. aureus) or intracellular (M. Tuberculosis)
• Structural components
• Metabolic products or toxins

Question 12

Write some notes on parasites and its antigens:

Answer 12

• Large (multicellular) (slower)
• Life cycle changes
• Radical changes in antigenicity

Question 13

What are the arms of the immune system?

Answer 13

• Direct neutralisation by antibodies
• Opsonisation and phagocytosis
• Complement mediated effects
• HLA restricted T cell mediated cytotoxicity
• NK cell mediated cytotoxicity
• Inflammatory and immunoregulatory cytokines
• Antiviral cytokines (i.e interferons)

Question 14

What do antibodies target?

Answer 14

Effective against antigens outside cells of body

• Viruses
• Toxins
• EC bacteria
• Parasites

Question 15

What do cytotoxic T cells target?

Answer 15

Effective against intracellular protein antigens

• Virus infections
• Tumour cells
• Transplanted organs

Question 16

How does bacteria trigger the immune system?

Answer 16

PAMPS i.e LPS, peptidoglycans

Local inflammation

• Vascular permeability changes
• Phagocyte recruitment
• Acute phase protein induction
• Local temp changes

== Phagocytosis and compliment activation

Question 17

What is the effect of antibodies and compliment against bacteria?

Answer 17

AB and compliment

• Prevent adherence or reduce mobility
• Enhance bacterial destruction (complement)
• Enhance phagocytosis (Opsonisation)

Question 18

How do bacteria avoid AB effects?

Answer 18

• Capsule resistance i.e heamophilus influenzae

- Intracellular growth i.e mycobacterium tuberculosis

Question 19

Describe how cells decide on NK or K lymphocyte activity:

Answer 19

This population of cells have a Antibody receptor (CD16) (ADCC). In addition they have a killer activating receptor + killer inhibitory receptor. (NK activity)

If the KAR+KIR bind a normal cell, theres antigens for both. IF it binds a abnormal cell i.e infected or tumour (down regulated HLA1). Then only KAR is activated and the NK cell attacks the abnormal cell.

If an antigen is recognised by CD16 then it has ADCC activity.

Question 20

What cytokines enhance NK activity?

Answer 20

IL2 and IFN-gamma enhances activity.

Question 21

Describe the time profile of acute viral infections:

Answer 21

• Interferon peaks first (Produced by infected cells to induce transient anti-viral state of neighbouring cells).
• NK activity follows quickly and peaks in activity
• Cytotoxic cells come last and antibodies.

Question 22

What are some pro-inflammatory cytokines and what do they do?

Answer 22

IL1, IL6, TNF-a

• Induce acute phase proteins
• Fever + Behavioural changes
• TNFa triggered by bacterial LPS
• Tissue repair: Bone reabsorption, fibroblast proliferation, collagenase synthesis, leukocyte adhesion.
• T and B cell activation

Question 23

What is the role of chemokines in infection?

Answer 23

• Aid chemotaxis

- Direct effector cell traffic

Question 24

What is the role of interferons in infection?

Answer 24

• Induce transient antiviral state
• Activate NK cell activity
• Upregulate MHC expression (improves CD8 T cells killing)