Introduction to immunology

Question 1

What is the immune system?

Answer 1

Vast communication network of cells and chemical signals distributed in blood and tissues throughout the human body which regulates normal growth and development of the organism while protecting against disease

Question 2

define immunity.

Answer 2

Condition/process in humans that permits innate and acquired/adaptive resistance to disease
Host needs to recognise non-self components and eliminate them (microbes).

Question 3

Where do the cells of the immune system arise from?

Answer 3

Cells of the immune system arise from pluripotent hematopoietic stem cells in the bone marrow.

Question 4

what are dendritic cells?

Answer 4

antigen uptake in peripheral sites and present these antigen to t cells.

Question 5

what are macrophages?

Answer 5

phagocytosis and activation of bactericidal mechanisms also antigen presenting.

Question 6

what are neutrophils?

Answer 6

phagocytosis and activation of bactericidal mechanism

Question 7

what are mast cells?

Answer 7

release of granules containing histamine and active agents.

Question 8

what cells are granulocytes?

Answer 8

Macrophages, neutrophils and mast

Question 9

where do t cells develop?

Answer 9

In the bone-marrow. Migrate to the thymus and are ”educated” in the thymus so they can distinguish between self-antigen and exhaustion antigens

Question 10

where do the b cells develop

Answer 10

Full development in the bone-marrow

Question 11

what makes up the immune system?

Answer 11

The primary lymphoid organs, the bone marrow where you have the development of all immune cells. Thymus also a primary lymphoid organs is where the maturation of the T cells finishes and the secondary lymphoid organs.

Question 12

what are the requirements of an effective immune system?

Answer 12

1. Must recognise wide range of infectious microorganisms including “new” ones
2. Defend against both intracellular and extracellular pathogens (tolerate commensals should mount an immune response against these bacteria)
3. Prevent or limit damage to self
4. Respond quickly

Question 13

what are the two types of immunity?

Answer 13

innate and adaptive

Question 14

how does an infection evolve?

Answer 14

Adherence to the epithelium, local infection there is penetration of the epithelium. the macrophages and dendritic cells will uptake the antigens and go to the lymph nodes where they will present the antigens to adaptive immune cells like the lymphocytes. After around 5 days this will drive the adaptive immune response.

Question 15

what are the features of innate immunity?

Answer 15

Epithelial barriers
complement system
pattern recognition
phagocytosis

Question 16

what are the mechanical epithelial barriers?

Answer 16

mechanical:
-epithelial cells joined by tight junctions
-longitudinal flow of air or fluid
-movement of mucus by cilia

Question 17

what are the chemical epithelial barriers?

Answer 17

fatty acids
low ph
enzymes
salivary enzymes
antibacterial peptides

Question 18

what are the microbiological epithelial barriers?

Answer 18

normal flora

Question 19

what is the complement system?

Answer 19

This is a system of (serum) proteins that are sequentially activated (cascade) to attach to pathogen surface, recruit inflammatory cells and killing of pathogens.

Question 20

what is pattern recognition?

Answer 20

Pattern recognition receptors (PRRs) recognize Pathogen Associated Molecular Patterns (PAMPs) – it is non specific.

They recognise something not from cell and should mount an immune response. They activate mechanisms to kill those pathogens.

Question 21

give examples of pattern recognition receptors?

Answer 21

E.g.: Toll Like Receptors (TLR)
* TRL2 recognizes peptidoglycan
* TLR4 recognizes LPS

Question 22

what is phagocytosis ?

Answer 22

Cells that “consume/eat” pathogens.

Question 23

give examples of phagocytic cells

Answer 23

• monocytes (in blood)
• neutrophils (in blood)
• macrophages (in tissue)
• dendritic cells (in tissues and blood)

these cells are Programmed to “recognize, eat and destroy”.

Question 24

what is the process of phagocytosis?

Answer 24

1. Macrophages are RECRUITED to site of infection through molecules like chemokines or from the complement system.
2. The macrophages BINDS to the microbe through pattern recognition, opsonisation (complement / antibodies).
3. The microbe is INTERNALISES microbe (phagocytosis) and forms the phagosome.
4. There is FUSION of phagosome with lysosome this process is called phagolysosome.
5. Finally there is KILLING of microbe with molecules that are inside of this phagolysosome nitrogen oxides, oxygen products.

Question 25

what cell bridges innate and adaptive immunity?

Answer 25

dendritic cells

Question 26

how does dendritic cells bridge innate and adaptive immuntity?

Answer 26

They are able to capture microbe and taken lymph node to induce ADAPTIVE immunity.

Once theses antigen presenting cells capture the pathogens the microbes are digested into small peptide fragments. This is called processing. Then are presentied

The dendritic cells come through the afferent lymphatic vessels. Present antigens a to the T cells where the T cells are activated.
Once the T cells are activated some will go to the germinal centre where the B cells are present and will activate the B cells and antibodies are made.

the activated B and T cells will then go to the infected site.

Question 27

what t lymphocytes are involved in cellular immunity?

Answer 27

There are two main types of T cells:
- CD4+ T cells (T helper cells: Th) are able to recognise antigen presenting cells that display MHC-II
- CD8+ T cells (T cytotoxic cells: Tc) are able to recognise anigen presenting cells with MHC-I

Question 28

what do cytotoxic tc do?

Answer 28

Cytotoxic T cells recognises complex of viral peptide with MHC Class I and kills infected cells.

Question 29

What happens after CD4+ Th cell activation?

Answer 29

1. Proliferation – once the C4+ naïve t helper cell recognises the antigen presented by the dendritic cells. The first step is clonal expansion/proliferation.
2. Differentiation into different effector t cells based on the cytokines present.
3. Effector functions, these effector cells have different functions:

Question 30

what does th1 cell do?

Answer 30

• Th1 leads to cellular immunity which leads to the recruitment of CD8+ T cells and macrophages which leads to pathogen elimination.

Question 31

what does th2 cell do?

Answer 31

• Th2 cells causes humoral immunity by b cells producing antibodies eliminate pathogens.

Question 32

what does th17 cell do?

Answer 32

• TH17 causes cellular immunity through the recruitment of neutrophils which eliminates bacteria and fungi

Question 33

what does Treg cell do?

Answer 33

• Treg causes cellular immunity by supressing or modulating immune responses this protects against autoimmunity.

Question 34

What is the most common immunoglobin?

Answer 34

IgG

Question 35

where are IgA mainly found?

Answer 35

• IgA mainly found in mucosal tissue

Question 36

What happens when things go wrong?

Answer 36

• Microbes can evade the immune system so Viruses hide inside cells (HIV).
• Cancers growing unchecked. Normal signals for growth and/or cell death fail.
• Harmless substances are deemed dangerous. Non-toxic substances causing allergies for an example peanut allergy.
• The immune system attacks itself Autoimmunity (eg.: diabetes, rheumatoid arthritis)