Clinical Immunology and Viral Pathogens - Strand B

What type of response does a parenteral vaccine produce?

Systemic immune response however no mucosal immune response.

Systemic and local IgG production.

What type of response does a mucosal vaccine produce?

Both systemic and mucosal immune responses.

Systemic and local IgG

Local SIgA production.

The urogenital tract is completely sterile.

True or False.

False.

It is sterile in parts but proximal parts of the urogenital tract host members of the human microbiota

Which mucosal surface contains no MALTs or M-cells?

Urogenital tract.

Why are there no MALTs or M-cells in the urogenital tract?

Adaptation for reproduction.

Anti-sperm antibodies can mediate immuno-infertility

Weaker Ig responses occur in the urogenital tract due to infections/immunization.

How is a strong antibody response produced?

Antibody input from systemic circulation are important in the immunity of the urogenital tract

What inductive sites can induce an immune response in urogenital effector sites?

Nasal inductive sites and vaginal inductive sites.

Where does IgG originate from when an immune response is initiated in the urogenital tract?

Can originate locally or from systemic circulation via transudation/exudation

What is transudation?

Flow of plasma filtrate across the epithelium

May represent a specific defence mechanism allowing passage of plasma immune elements such as IgG

What is exudation?

Build up of fluid caused by tissue leakage due to inflammation or local cellular damage

Why are parenteral and nasal vaccinations useful for STIs?

Urogenital tract has a large number of antibodies in circulation and a strong humoral response is generated there in response to systemic and intranasal immunizations

How does the adaptive immune system protect against a urogenital virus infection?

1) CD4+ T-cells block viral replication via IFN-gamma

2) CD8+ T-cells kill virally infected cells

3) Immunoglobulins of local and systemic origin block virus entry into cells

What type of pathogen is Trichomonas vaginalis?

Parasitic protist

STI

What type of pathogen is Neisseria gonorrhoeae?

Bacteria

STI

What type of pathogen is Chlamydia trachomatis?

Bacteria

STI

What type of pathogen is Treponema pallidum?

Bacteria

STI

What treatment can be given to HIV patients to reduce the viruses impact?

Highly active antiretroviral therapy (HAART)

What type of epithelial cells does HPV infect?

Stratified squamous epithelium and targets basal keratocytes

What HPV protein is used in HPV vaccines?

Prophylactic vaccines use HPV L1 protein

HPV requires tissue damage for the initial infection of basal keratinocytes.

True or False?

True.

HPV needs access to the keratinocytes deep in the epithelial layer.

This means tissue damage can allow HPV to infect.

What cell type in particular does HIV infect?

CD4+ T-cells which results in destruction of the immune response in an infected individual.

What five unique steps in HIV’s life cycle are targeted by antiretroviral drugs?

Binding

Fusion

Reverse Transcription

Integration

Proteolytic cleavage

Where do most HIV infections occur through?

Mucosal surfaces.

~10 to 1 compared to other sites

What type of transmission accounts for 80% of all HIV transmission?

Heterosexual transmission (from intercourse)

How can HIV be transferred from mother to child?

• In utero (by amniotic fluid)

• During birth (by infected blood/cervical secretions

• Breast feeding (by virus particles in the milk which mediate infection through the gut)

What are Langerhans cells?

Type of dendritic cell

How can Langerhans cells contribute to HIV infections?

Can capture cell associated HIV and transmit HIV to T-cells and other immunocytes

Can also migrate to draining lymph nodes, further spreading the virus

Breast milk or semen contaminated with HIV can enter the GI tract. How does HIV then cross the epithelial membrane?

HIV can pass through the simple epithelium easily.

• Via endocytosis

• Via dendritic cells

• Via cellular damage

Mucosal infection by what pathogens can increase HIV-1 transmission across the gut mucosa?

Bacteria vaginosis and Trichomonas vaginalis

Why is a HIV vaccine hard to develop?

HIV has a fast rate of evolutionary change and fast immune evasion

High-titre broadly HIV-neutralising antibodies are not typically induced by HIV infection or vaccination

What types of respiratory immune defences are there?

• Microbiota

• Filtration and clearance mechanisms to remove particles/pathogens

  • Filtration in nasal cavity

  • Muco-ciliary clearance along trachea

  • Macrophages ingesting particles/pathogen in alveoli

• Mucosal immune system

  • Innate response (epithelial cells, macrophages, dendritic cells, neutrophils, etc)

  • Adaptive response (T-cells, B-cells, SIgA and IgG)

Where in the airways are NALTs typically found?

Upper airways

• Nasal passages

• Sinuses

• Pharynx

Where in the airways are BALTs typically found?

Central airways

• Trachea

• Bronchi and bronchioles

• Typically present in children but not adults

Lower airways

• Respiratory bronchioles

• Alveolar ducts, sacs and alveoli

What is surfactant and what its role?

Lipid-protein complexes which facilitate gas exchanges at the alveoli

Contribute to stimulating host defences

Also help reinflate alveoli by reducing surface tension

What type of immune cells are found in the middle airway?

Ciliated EC

Goblet EC

Dendritic cells

Macrophages

T-cells

B cells

AEC (Airway Epithelial Cells)

What type of immune cells are found in the lower airway?

Type I AEC

Type II AEC

Dendritic cells

Macrophages

T-cells

What is antigenic shift in influenza?

Major change in influenza virus antigen due to gene assortment

What is antigenic drift in influenza?

Minor change in influenza virus antigens due to gene mutation

What is a cytokine storm?

Excessive, dis-regulated cytokine production

This leads to severe inflammation and multi-organ damage (Sepsis)

What is Sepsis?

The bodies uncontrolled reaction to an increase in the amount of cytokines (cytokine storm)

This leads to organ damage and potentially organ failure.

Can also lead into septic shock

What is septic shock?

The most severe stage of sepsis which results in a huge drop in blood pressure and organ failure.

What are some of the advantages of mRNA vaccines?

Once the virus is sequenced, there’s no need to manipulate it

Well tolerated by, and effective in all age groups

If variants appear, the mRNA sequence can just be modified

What is the function of secretory IgA (sIgA)?

sIgA plays a critical role in mucosal immunity by preventing pathogen adherence and invasion.

What immune responses occur in the urogenital tract?

Relatively weaker immune (Ig) responses are induced locally through infections and immunizations, with antibodies from circulation (IgG and monomeric IgA) playing an important role.

Which immunoglobulin class is dominant in mucosal secretions?

Secretory IgA (sIgA) is the dominant class in mucosal secretions.

Where are NALTs found?

Digestive tract

Respiratory tract

Urogenital tract

Oral NALT inductive sites cause immune responses where?

Cause immune responses in GI tract and mammary gland effector sites

Nasal NALT inductive sites cause immune responses where?

Cause strong immune response in respiratory tract effector sites

• Also cause a immune response in reproductive tract effector sites

What type of cells are important for antigen sampling at NALTs?

M-cells

What type of cells are important for antigen sampling at GALTs?

M-cells and Dendritic cells

What are Peyer’s patches?

Small clusters of lymphatic tissue in the gut.

M-cells catch and transport antigens from the gut lumen to basal membrane to present them to intestinal lymphocytes

The majority of antigens encountered by GALTs are derived from where?

Beneficial bacterial members of the gut microbiota

How many bacteria does the stomach contain and why?

Very few bacteria in the stomach

• Due to the high acidity of gastric juices

Which has a higher abundance of bacteria? Small intestine or Colon?

Colon has an extremely high abundance of bacteria.

The small intestine has fewer bacteria but still more bacteria than the stomach

What are the 5 key roles of the GI microbiota?

• Detoxification

• Biosynthesis

• Immune maturation

• Metabolic roles

• Protection from pathogenic bacteria

How does the GI microbiota perform detoxification?

Can absorb xenobiotics (molecules foreign to host) and turn them into harmless metabolites

What is an example of the GI microbiota doing biosynthesis?

Gut microbiota can produce menaquinone which is also known as vitamin K2.

• The body can use vitamin K2 for various important processes

How does the GI tract microbiota induce immune maturation?

Beneficial bacteria present antigens to the maturing immune system and induce mucosal T-cell and IgA plasma cell development

Also help train the immune system to differentiate beneficial and pathogenic bacteria

What is an example of the GI tract microbiota’s metabolic role?

Gut microbiota can turn indigestible fiber into short-chain fatty acids which is the main energy source for epithelial cells of the colon

SCFAs are also absorbed systemically have have various functions around the body

How does the gut microbiota help protect against pathogens?

Gut microbiota can produce anti-microbial peptides which can help defend against pathogens

Gut microbiota can also prevent pathogen growth by out performing pathogenic bacteria and compete for resources

SCFAs stimulate Goblet cells to do what?

Secrete more mucin.

SCFAs stimulate T-reg cells to do what?

Secrete the anti-inflammatory cytokine IL-10

Why can antibiotics have a negative impact on the gut microbiota?

Kill both pathogenic and beneficial bacteria.

This can cause a shift in biomass and allows for certain bacteria (e.g. Clostridium difficile) to thrive

What can a Clostridium difficile bloom in the gut cause?

Clostridium difficile can damage the epithelial barrier and lead to chronic bloody diarrhoea

Many strains of C. diff are also multi-drug resistant meaning antibiotics will not treat it.

What is sometimes the only effective treatment for an overgrowth of C. diff in the gut microbiota? Why can antibiotics not be used?

Since many strains are multi-drug resistant, sometimes a faecal transplant is the only effective treatment

How does the microbiota stimulate the producing of a healthy mucus layer?

Microbiota is recognised by the immune system which stimulates the production of Mucin and Anti-microbial peptides WITHOUT inducing inflammation

This keeps the microbiota away from the epithelial cells while maintaining a healthy mucus layer

How do some members of the microbiota block pro-inflammatory pathways?

Some members can interfere with NF-kB pathway of epithelial cells to block pro-inflammatory pathways

If a bacteria manages to cross the epithelial barrier, what happens?

Any bacteria which crosses the epithelial barrier will be killed by macrophages

Why do intestinal macrophages not trigger strong inflammatory responses?

When they recognise and kill bacteria, they do not secrete pro-inflammatory mediators.

• This prevents a strong inflammatory response being generated

What are Overt pathogens?

Microorganisms which cause disease upon infection

• Usually not present in the entire host population

What are Opportunistic pathogens/Pathobionts?

Microorganisms which cause disease under some circumstances

• Sometimes are normal members of the microbiota which cause disease during dysbiosis

What is a Parenteral vaccination?

A vaccination which avoids the GI tract.

• Intramuscular vaccinations

• Intravenous vaccinations

• Sub-cutaneous vaccinations

Which mucosa are Parenteral vaccinations effective for and why?

Urogenital and lower respiratory tracts

• These are permeable to serum derived IgG so Parenteral vaccinations work well

When do Parenteral vaccinations not work well?

If the target pathogen is restricted to mucosal surfaces which are not permeable to IgG (e.g the gut)

The oral polio vaccine (OPV) is what kind of vaccine?

Live attenuated vaccine

The Oral Polio Vaccine (OPV) triggers production of which immunoglobulins?

Triggers production of both SIgA and IgG

• This means it can protect against mucosal and systemic infection

The Inactivated (killed) Polio Vaccine (IPV) triggers production of which immunoglobulins?

Only triggers production of IgG

• This means it can only protect against systemic infection and cannot prevent mucosal infection

The Rotavirus RotaRix vaccine is what kind of vaccine?

Attenuated virus vaccine

The Rotavirus RotaTeq vaccine is what kind of vaccine?

A Bovine-human reassortment vaccine composed of five rotavirus strains

• Each strain contains a human rotavirus gene encoding the VP7 neutralising protein

Both the Rotavirus RotaRix and RotaTeq vaccines cause what kind of immune response?

Both an SIgA response and a cellular immune response

What are Inner-epithelial lymphocytes (IELs)?

Important lymphocytes for controlling mucosa repair

• CD8+ IEL are active against intracellular pathogen (e.g. viruses) infected cells and tumour cells

Sit between and around epithelial cells and protect them

What are the functions of SIgA?

• Bind and neutralise pathogen/toxins

• Bind and neutralise antigens internalised in endosomes

What are the three fundamental levels of mucosa defenses?

• Immediate Innate immunity

• Induced innate immunity

• Adaptive immunity

What are some examples of immediate innate immunity?

• Tight junctions/mucus

• Antimicrobial peptides

• The microbiota

• Lysozymes

How is mucus cleared?

Ciliated cells propel the mucus away via movement of cilia

Muscle contractions can also move mucus along mucosal surfaces (e.g. sneezing/coughing)

What is the surface of epithelial cells which faces organ cavities called?

Apical membrane.

These face the air (lungs) or organ cavities (gut)

What is the ‘inner’ surface of epithelial cells called?

Basolateral membrane.

These mediate cell-cell interactions and extracellular matrix interactions.

Which surface of an epithelial cell can potentially have cilia?

Apical surface.

What is transcytosis?

Vesicular mediated transport of internalised material of endogenous or exogenous origin.

List some immune functions of epithelial cells.

Barrier functions

• Secrete innate and adaptive molecules

  • E.g. mucins/AMP and SIgA)

Integrates innate and adaptive defences

• TLR and NOD receptors sensing microbes leading to AMP/mucin secretion

• Antigen uptake and processing

Regulates defences

• Integrate signals from the microbiota, pathogens and immune cells

• Secrete mucosal immunoglobulins (SIgA)

What are the three key innate immune functions of epithelial cells?

• Can sense pathogens via TLR/NOD receptors

  • These activate NFkB which induce cytokine production to recruit immune cells

• Inflammasome can induce cytokines

  • Increases barrier integrity and recruits immune cells

• Epithelial cells can perform xerophagy which is a type of autophagy which can destroy some pathogens.

What majority of immune cells are involved at (or in transit between) mucosal surfaces?

~80% of immune cells

Where are mucosal immune cells activated?

Mucosal Associated Lymphoid Tissues (MALTs) and/or local mucosa-draining lymph nodes

What two sites is the mucosal adaptive immune system made of?

Inductive sites

• Antigen capture and presentation to naive B/T-cells

• Organised in some mucosa to MALTs

Effector sites

• Effector lymphocytes migrate here to carry out their functions

  • Lamina propria

  • Exocrine glands

  • Surface epithelia

Where are innate immune cells found at mucosal surfaces?

Dispersed within the lamina propria and/or squeezed between epithelial cells

What are the three major MALTs and where are they found?

NALT

• Nasopharynx, respiratory and digestive tract

GALT

• Respiratory tract

BALT

• Gut-digestive tract

Which mucosal surface has no MALT present?

Urogenital tract

What chemokines are secreted in effector sites to attract/retain CCR9/CCR10 expressing B-cells in the gut?

CCL25(Small bowel)

CCL28 (Large bowel)

What are the two ways the mucosal surfaces can overcome the problem of a physical barrier separating antigens and immune effector cells?

Antigens sampled by specialised cells

• M-Cells

• Cross-epithelial macrophages/DCs

• Macrophages in alveoli

IgA and IgM are transcytosed into the lumen to contribute to pathogen elimination

How do M-Cells sample antigens from the gut lumen?

Antigens taken up via endocytosis/phagocytosis

Antigens then transported across cell via transcytosis