Immunology Revision

Define the term “pathogen”

A disease causing agent

Define the term “disease”

A malfunction of the body that has an adverse effect on good health.

Define the term antigen

A marker used for your immune system to tell whether something is harmful or not.

Name 2 ways pathogen can cause disease

• Release toxins and harmful chemicals in the body

• Replicate faster than can be removed.

Compare self and non-self antigens

Self antigens are recognised by immune cells as not harmful and hence are not attacked, therefore do not trigger an immune response.

Non-self antigens are displayed on MHC-I markers of infected cells and are identified by immune cells as harmful and is attacked by triggering an immune response.

What is the first line of defence?

Physical, chemical and microbial barriers that prevent pathogens from entering the internal environment of the body.

Name 3 examples of physical barriers

1. Intact skin

2. Mucosal membrane

3. epithelial cells in the respiratory system, gastrointestinal track and urogenital track.

Name 2 examples of chemical barriers

1. Lysozyme in tears

2. Stomach acid

Name 1 example of microbial barriers

1. Natural gut flora

Name 3 ways disease can spread

1. Inhalation of respiratory droplets contaminated with pathogens

2. Direct contact with pathogen contaminated surfaces

3. Consumption via food and drink

Name 2 physical barriers in plants

1. Intact bark

2. Waxy cuticles

Name 2 chemical barriers in plants

1. Caffeine (kills fungi)

2. Defensins ( kills microbes)

Name a microbial barrier in plants

Plant roots near colonies of non-pathogenic bacteria.

Outline the steps of the inflammatory response.

1. Infected cells release cytokine to attract neutrophils to the area of infection.

2. Neutrophils perform phagocytosis and release cytokines to attract macrophages and dendritic cells to aid with phagocytosis.

3. Complement proteins activated and attach to pathogen, performing opsonisation and forms membrane attack complex.

4. Mast cells release histamine, causing blood vessels to dilate (vasodilation) to increase blood flow to area of infection and brining in more leukocytes. Blood vessels also become more permeable to allow leukocytes to easily access area of infection.

5. After infection is cleared, macrophage and dendritic cells phagocytose debris from infection site.

Function of neutrophils

• Performs phagocytosis

• Respond rapidly to cytokine signals released from infected cells.

• Release cytokine to attract other immune cells.

Macrophage and Dendritic Cells

• Performs phagocytosis

• Have MHC-II markers, therefore can engulf pathogen and present antigen on MHC-II marker (antigen presentation).

• Carries antigen to lymph node + present to specific T helper cell.

• Release cytokine to attract other immune cells.

Function of mast cells

• Release histamine

• Histamine causes vasodilation and permeability of blood vessels.

Function of Natural killer cells

• Identifies foreign antigen on MHC-I markers or damaged MHC-I markers on cancer cells.

• Destroys infected or cancerous cell by releasing perforin, which perforates cell and initiates cell lysis, resulting in apoptosis.

• Not specific to a particular antigen (unlike cytotoxic T cells).

Eosinophils

• Targets large, multicellular pathogens such as parasites.

• Destroys parasites by releasing perforin and granzymes that damages their cell membrane.

Functions of interferons

• Signalling molecule

• Released by virally infected cells

• Warns other cells near by about presence of virus.

• Nearby cells reduce permeability of cell membrane to reduce suseptability to infection.

• Inhibits certain virus’s ability to synthesis new viral proteins within host cell.

• Attracts NK cells.

Functions of complement proteins

• Directly attack bacterial plasma membrane by forming membrane attack complex (MAC).

• Enhance phagocytes’ ability to clear pathogens.

• Assist in recruitment of WBC to the site of infection.

• Coat pathogenic microbes to make them more visible to phagocytes.

Outline the steps of phagocytosis.

1. Phagocytes engulf pathogen and forms a phagosome.

2. Lysosome migrates to phagosome and fuse with phagosome, releasing lysozymes into phagosome.

3. Lysozyme break down pathogens

4. Antigen of pathogen displayed on MHC-II markers of macrophage and dendritic cells.

Side effects to inflammatory response

• Redness: caused by vasodilation and increase of blood flow to infection site.

• Swelling: increase permeability of blood vessel releases fluids.

What’s the purpose of a fever?

Slows down pathogen replication and speeds up immune response.

Define allergen.

A substance that can cause an allergic reaction.

Define allergy

A malfunction in the immune system, where the immune cells mistakingly identified allergens as a threat.

Outline the process of an allergic response.

1. Dendritic cell engulf allergen and present on MHC-II to specific T helper cell.

2. T helper cell selected, and release cytokines to activate B naive cell that has also encountered allergen.

3. B naive cell undergoes clonal expansion and differentiates into memory B and plasma B.

4. Plasma B produce IgE antibodies, which bind to mast cells.

5. Allergen reenters body and reacts with IgE on mast cells, causing mast cells to degranulate and release histamine.

6. Histamine cause vasodilation and mucus secretion and triggers inflammatory response in serious allergies.

7. Results in symptoms of allergic reaction.

Define vaccine.

Vaccine is a medical treatment typically containing antigen designed to stimulate a person’s adaptive immune system to create immunity to a pathogen.

What’s the purpose of booster vaccines?

Booster shots reinforces immunological memory by stimulating remaining memory cells to produce more plasma B as well as B and T memory cells to restore immunity.

What is herd immunity

When majority of the population (approx. 95%) gains immunity to an infectious disease, thereby limiting the spread.

What are vaccination programs?

Series of vaccinations designed to create long term immunity to a disease.

What is the purpose of vaccination programs?

• Protect vulnerable people who cannot get vaccinated.

• Eradicate disease by decreasing incidence and number of hosts available for pathogen to infect.

List and describe the type of vaccines. (SLIMT)

• Subunit vaccines: uses specific piece of pathogen.

• Live- attenuated vaccines: contains weakened version of living virus that cause no serious disease.

• Inactivated vaccines: contains dead pathogens killed by heat or chemicals.

• mRNA vaccines: gives cells instruction to code for viral protein to which the body produce antibodies.

• Toxoid vaccines: contains toxins made by pathogen.

What is the lymphatic system?

A network of lymph vessels, primary and secondary lymphoid organs and lymph.

List the primary lymphoid organs.

• Bone marrow

• Thymus

List the secondary lymphoid organs

• Spleen

• Lymph nodes

• Tonsils

• Appendix

Role of antibodies (ANAPO)

• Agglutination: Bind to foreign antigens and viral particles and clumps antigens together to make it easier for phagocytes to phagocytose.

• Neutralisation: Neutralises toxins released by pathogens.

• Activate complement system: activate complement proteins to perform their duties.

• Precipitation: bind to viral particles to make them solid.

• Opsonisation: make them easier to identify and find by phagocytes and enhances phagocytosis.

What is the function of MHC-I markers?

• For immune cells to identify infected/unhealthy cells from healthy nucleated cells.

• Healthy nucleated cells have undamaged MHC-I markers and are not destroyed by leukocytes.

• Infected or cancerous cells present pathogen antigen on MHC-I or have damaged MHC-I and are destroyed by leukocytes.

Compare and contrast bacterial infections and viral infections.

Bacterial:

• Can be intracellular or extracellular

• Relies more on humoral response.

Viral:

• Intracellular only

• Relies more on cell-mediated response.

Both:

• Involve T helper cells

• Involve antibodies produced by plasma B

• Create memory of pathogen via memory T and B.

• Involve antigen presentation stage.