Lecture (20) : Blood and immune

Question 1

What are the constituents of blood?

Answer 1

• Plasma (Water and dissolved substances)
• White Blood Cells and Platelets
• Red blood cells (synonymous with erythrocytes)

Question 2

What are the types of white blood cells?

Answer 2

Neutrophils
Lymphocytes (T and B cells)
Monocytes (i.e macrophages)

Question 3

What is the function of the immune system?

Answer 3

Defence system, it must;

1) Differentiate self from non self (if it gets it wrong or confused then you can have autoimmune disease)
2) Seek and destroys pathogens / material that is not you

Question 4

Define pathgen:

Answer 4

Something that causes disease i.e bacteria, virus, prion, fungi

Question 5

Define antigen:

Answer 5

A molecule/ molecular shape that induces an immune response via a lymphocyte (generic definition…)

NB: Pathogens have many antigens on their surface (antigens are any molecules that can be recognized)

Question 6

Define antibody:

Answer 6

A molecular component of the immune system that recognizes and binds (interacts with) antigens

Question 7

What is innate immunity? How can it be divided?

Answer 7

Innate immunity are the features of the immune system that are always deployed / ready to engage.

Can be divided into external / first line of defense and internal/second line of defense.

Question 8

What are some examples of external innate immune factors?

Answer 8

First line of defense: In essence the barrier to the internal body.

• Skin
• Secretions (Context: saliva contains immune molecules, enzymes (examples of context, Do Not Learn (DNL))
• Mucous membranes ( Context: lungs produce mucus that traps foreign particles and defends against bugs, DNL)

Question 9

What are some examples of internal innate defenses?

Answer 9

Second line defenses:

• Phagocytic cells
• Natural Killer cells
• Defensive proteins
• Inflammatory response

NB: “Humoral” factors is a term chucked around a lot and simply refers to molecules that create the immune response, not cells.

Question 10

What is adaptive immunity?

Answer 10

An immune response that results in long term changes

i.e Immune cells activated by exposure to specific pathogens (lymphocytes)

Question 11

What are the cells of adaptive immunity?

Answer 11

Lymphocytes:

• T cells (T helper (CD4), cytotoxic T cells (CD8))
• B cells
• Plasma B cells (Antibody producing)

Question 12

Whats the role of the lymphatics system?

Answer 12

Involved in internal innate immunity and adaptive immunity

Question 13

What is the role of the internal innate immune system? (2 roles) Give some specific details on the roles

Answer 13

To recognize pathogens and initiate an immune response. They are constant surveyors of the internal environment.

Two Roles: Phagocytosis and Inflammation

More specifically:
-> Initiate inflammation
i.e Vasodilation of blood vessels at sites of injury or infection.
Also increasing permeability of blood vessels
Chemotactic cytokines to attract other immune cells to sites of injury or infection.
-> Phagocytosis of pathogens
-> “Cleanup and repair”

Question 14

What is the role of the external innate immune system?

Answer 14

In essence it is a barrier to prevent the movement of pathogens into the body

NB: Humans are like donuts, so the lumen of the gut is considered external. It also means the microbiome, that is the natural bacterial environment covering every external part of our body is considered part of the external innate immune system as they like to rule the land and dont want other pathogens invading their territory.

Question 15

What do natural killer cells do and are they involved in innate or adaptive immunity?

Answer 15

Internal innate immune factors

Natural killer cells recognition and killing of virus infected and cancer cells.

Question 16

Describe the 3 step process of inflammation:

Answer 16

1) Tissue injury; Release of chemical signals i.e histamine
2) Histamine causes: Dilation and increase leakiness of local blood vessels (fluid enters tissue and causes swelling); Migration of phagocytic cells to the area. (fluid factors also help with healing and clotting.)
3) Phagocytic cells activated, recognize and engulf bacteria and cell debris.

Question 17

Describe the process of phagocytosis:

Answer 17

Phagocytes i.e neutrophils, monocytes/macrophages, engulf and digest bacteria or cell debris.

• Cell receptors recognize bacterial antigens
• Phagocyte engulfs bacteria into ‘phagosome’
• Lyosome filled with acidic factors i.e H2O2 merges with phagosome to form a phagolysosome.
• Bacteria is broken down
• Debris are released from the phagocyte

(NB antigen presenting cells might display some fragments on the surface of the cell to active lymphocytes)

Question 18

Write some notes on the origin of B and T cells:

Answer 18

B cells: Develop and specialize in bone marrow (produce Antibodies)

T cells: Develop in bone marrow and mature in thymus.

Question 19

How are B and T cells activated?

Answer 19

Activated by exposure to SPECIFIC pathogens

i.e SPECIFIC shapes of receptors detect SPECIFIC pathogens

Question 20

How do we end up with enough B and T cells to recognize all pathogens?

Answer 20

• Born with massive repertoire of B and T lymphocytes.
• Each one recognizes a specific antigen
• Specificity RANDOMLY PRODUCED by rearrangement of the genes coding for the B and T cell ANTIGEN RECEPTORS

Question 21

Describe the the two important characteristics of antigens:

Answer 21

1) Immunogenicity: The ability to provoke an immune response by stimulating the production of antibodies or T-Cells.
2) Reactivity: The ability of the antigen to react specifically with the antibodies or cells it provoked.

Question 22

What are epitopes of antigens and why are they important?

Answer 22

Epitopes are regions of the antigen that can be recognized, and each antigen typically has several epitopes that can be recognized by Antibodies or T cells

Question 23

What happens once a lymphocyte recognizes an antigen?

Answer 23

Antigen recognition activates lymphocytes to undergo ‘clonal expansion’ that mediate adaptive immunity.

Question 24

Describe the antibody concentration/time profile following a primary and secondary response to an antigen:

Answer 24

Following the first exposure to an antigen it takes around 7 days for antibodies to start being produced. Peaking around 17 days, lasting ~23 days.

Following the second exposure to the same antigen the antibodies are produced within a few days and peaks around 7 days but at 4x the concentration and lasts a long time at this higher concentration. (Memory B and T cells can live in lymph nodes for decades)

• This is the basis for infection induced immunity and vaccination

Question 25

What is the secondary response to an antigen like? (generic concept)

Answer 25

Much faster, stronger and lasts longer than the first first.

Question 26

Describe how the adaptive immune response can be activated following a splinter infection:

Answer 26

• Bacteria divide rapidly. Even if phagocytes are efficient, can often require help.
• A B-cell with a matching receptor binds to the bacteria with the non-self antigen, it can then activate and start producing antibodies. Antibodies mark pathogens for destruction.
• T cells can also recognize antigens and help the B-cells in their quest.

Question 27

What do B cells also do?

Answer 27

Produce antibodies and divide to produce memory be cells for future infections for that rapid secondary reponse.

Question 28

How are Sars-cov2 antibodies used to understand the pandemic?

Answer 28

• Antibodies are an important marker of previous infection. (serology based assays)
• Used in an antibody assay to:
  1) Detect historical infections
  2) Estimate prevalence
  3) Understand persistence and protection (i.e how long ABs last)

Question 29

How is serology used for an individual vs a population:

Answer 29

Individual: Single persons infections or vaccination history

Population: Serosurvery, estimate prevalence and indicator of exposure. (blood sample from pop)

Question 30

Write some bullet point notes on antibodies:

Answer 30

• Adaptive immune response
• Highly specific molecules
• Can be measured to understand infection and vaccination status of an individual

Question 31

Write some bullet point notes on adaptive immunity:

Answer 31

• Defense against specific antigens
• Has memory of prior antigen encounters
• Response is highly specific/effective but slower