Foundations in Immunology.

Question 1

Explain the main role of the immune system and how it carries out this role.

Answer 1

The immune system is the body’s barrier against infection from the microorganisms (pathogenic) in our environment. This is achieved by the coordination of the innate and acquired/adaptive systems.

Question 2

Name the major cells of the innate immune system, and the role they play.

Answer 2

Phagocytes
Eosinophils
Mast cells
NK cells
Cytokines
Basophils
Complement (not a cell but a system of proteins)
- The innate immune system is the body’s first line of defence, the cells are non-specific and have no memory.

Question 3

Describe dendritic cells.

Answer 3

Dendritic cells (or professional antigen presenting cells).
Their main function is to sample microorganisms (by phagocytosis).
Process these microorganisms.
Present the antigen to other cells via their MHC (major histocompatibility complex).

Question 4

Describe phagocytes.

Answer 4

Phagocytes are the cells of the immune system that track down, engulf and destroy bacteria, pathogens and their own damaged or diseased cells.

Question 5

Describe the process of phagocytosis.

Answer 5

The phagocyte encounters a pathogen that binds to the cell membrane. The phagocyte uses its cytoskeleton to push its cell membrane around the pathogen (endocytosis), creating a large vesicle = phagosome.
The phagosome separates from the cell membrane (with the pathogen inside) and moves into the cytoplasm.
The phagosome fuses with the lysosomes containing digestive enzymes and the pathogen is killed and digested within the vesicle. Waste materials are then discharged.

Question 6

Describe eosinophils.

Answer 6

Eosinophils help combat parasitic infections, they attach to large anti-body coated parasites and release substances from their granules (may contain enzymes) that damage or kill the parasite.
Involved in allergy and asthma.

Question 7

Describe mast cells.

Answer 7

Mast cells are situated in the body where it is convenient of them to intercept pathogens, they release histamine as a result of the process of degranulation, which was triggered by the activation of an allergic reaction. Once histamine is released into the blood stream, the allergic response occurs. The responses in different parts of the body can differ.
E.g. when histamine reaches the; skin - itchiness; lung - contraction, blood vessels - dilation, stomach - gastric acid secretion.

Question 8

Describe basophils.

Answer 8

Basophils are rare in the circulation and contain large cytoplasmic granules with inflammatory mediators. They are found near the site of infection or near the parasite.
**no proven function.

Question 9

Describe the role of cytokines.

Answer 9

Cytokines are small proteins that are secreted by both immune and non-immune cells in response to stimulus.
They communicate with other cells.
They bind to specific receptors on these other cells producing a signalling molecule that leads to many biological effects in these cells.

Question 10

Define primary lymphoid organs.

Answer 10

Primary lymphoid organs are places where blood cells are produced and acquire their ability to interact with antigens.
- Bone marrow
-Thymus

Question 11

Describe secondary lymphoid organs.

Answer 11

Secondary lymphoid organs are sites of lymphocyte activation by antigens.
AKA where the development of adaptive immune response to Antigens by B and T-cells.
- Lymph nodes
- Spleen
- Mucosal immune system
- Tonsils

Question 12

Define the function of “lymphoid organs”.

Answer 12

Lymphoid organs are where lymphocytes are formed and mature.
Lymphocytes are the primary effector cell for the antigen-specific responses of adaptive immunity.

Question 13

Describe “T lymphocyte” T-cells.

Answer 13

Responsible (along with NK cells) in defence against intracellular microorganisms.
These T-cells mature within the thymus and can have 2 forms,
CD4+ - T-helper cells
CD8+ - Cytotoxic cells T-helpers.

Question 14

Describe the features of both types of T-helper cells.

Answer 14

T-helper 1:
T-helper 1 cells help to protect the body against intracellular microorganisms
T-helper 2:
T-helper 2 cells help to protect the body from extracellular microorganisms.
Both types of T-helper cells can only identify antigens when they’re bound to the MHC 2
These T-helper cells stimulate the B-cells to produce the antibody.

Question 15

Describe the features of cytotoxic T cells (Tc).

Answer 15

These cells express the CD8+ co-receptor. They are responsible for killing virus infected cells (via apoptosis).
Upon recognition of infected cells, they secrete perforin and granzyme.
They only recognise antigens when they’re bound to MHC 1.

Question 16

Describe the process of antigen processing and the T-cell interactions involved.

Answer 16

Once the microorganism is taken up and sampled by the phagocytes, it is then presented on the MHC to circulating T-cells.
The T-cells detect the presentation of the microorganism by T-cell receptors (TCRs).
From this detection there are two possible routes, 1) the release of cytokines to enhance inflammation or 2) stimulation of B-cells.

Question 17

Explain the role played by B-cells in immunity

Answer 17

Once a microorganism has reached the T-helper cells, it is presented to B-cells via the B cell receptors.
From that point, the B-cells produce high affinity antibodies that are specific for the microorganism concerned.
The microorganisms are then tagged by the antibodies for elimination by immune process.

Question 18

Describe the structure of antibodies.

Answer 18

Antibodies are proteins that are produced as an immune response against antigens.
Antibodies can be separated into two regions;
The upper region is called the antigen binding region, the specific part of the antibody that recognises and interacts with the antigen.
The lower region is called the Fc region.

Question 19

Describe the function of antibodies.

Answer 19

Neutralization - prevention of attachment and entry.
Opsonisation - facilitate the uptake of microbes by phagocytes including macrophages so they facilitate phagocytosis.
Complement activation - Classical pathway.

Question 20

Describe the role of the complement system

Answer 20

The complement system is a humoral form of innate immunity and its role is to help clear/kill pathogens within the body.
There are 3 main outcomes of the complement system;
1) Enhanced phagocytosis
2) Lysis of cell
3) Promotion of inflammatory processes.

Question 21

Describe active immunity.

Answer 21

Active immunity is produced by the hosts own immune system, and it takes weeks to develop. Memory cells are produced with active immunity and the protection provided is permanent.

Question 22

Describe passive immunity.

Answer 22

Passive immunity is the transfer of antibodies/cells from another individual, and it happens immediately. There are no memory cells (B-cells) present and the protecting provided is temporary.

Question 23

Describe the function of neutrophils.

Answer 23

Neutrophils are the most abundant type of WBC in the body.
They track down, engulf and destroy pathogens.
They contain granules that are filled with many destructive enzymes such as peroxidases, alkaline and acid phosphatases which are responsible for killing and destroying bacteria and other pathogens.
Neutrophils also release cytokines out of the cell to activate other immune cells. This ultimately amplifies the immune response.

Question 24

Describe the function of macrophages (monocytes).

Answer 24

Macrophages can engulf larger pathogens.
They break down pathogens, process specific components, called antigens and present the processed antigens to the cells of the adaptive immunity to produce specific immune response in the form of Ab and cytotoxic cells.