Lecture 30 - Introduction to immunology and the immune system

Question 1

What is immunology?

Answer 1

The study of an organism’s defence system (immune system) in health (homeostasis) and in disease

Question 2

What is the immune system?

Answer 2

An organised system of organs, cells and molecules that interact together to defend the body against disease (e.g. pathogenic microorganisms and cancer)

Question 3

What is the immune system comprised of?

Answer 3

Organs (e.g. spleen)
Cells (T cells etc.) - the cells of the immune system are all throughout the body therefore the immune system is absolutely everywhere in the body
Molecules (antibodies)

Question 4

Why is immunology so important?

Answer 4

If you do not have an immune system you are very susceptible to diseases

You need a working immune system to fight infectious diseases e.g. HIV/AIDS or against SARS-CoV-2 (covid 19)

Question 5

What are microbes?

Answer 5

a microscopic organism, which may exist in its single-celled form or in a colony of cells

Cannot see microbes under a light microscope, have to use an electron microscope

Question 6

Pathogens

Answer 6

Some microbes are pathogens (disease causing)

Question 7

Primary lymphoid organ

Answer 7

production of white blood cells/lymphocytes

Bone marrow (in long bones) - source of stem cells that develop into cells of the innate and adaptive immune responses (these stem cells have the ability to develop into different cell types depending on the environment and the signals they receive - pluripotent cells)

Thymus - ‘school’ for the white blood cells called T cells. Developing T cells learn not to react to themselves (learn to recognise pathogens and to not react to themselves. If they are not able to recognise a pathogen or if they react to themselves, they end up being killed off - around 10% of T cells make it through the ‘school’ and end up being able to leave the thymus and move around the body) (the thymus itself starts off in life quite large and as you grow up it shrinks)

Question 8

Secondary lymphoid organ

Answer 8

sites where immune responses are initiated. Provide an environment for the optimal interaction of antigen with T and B cells.

Spleen - Site of initiation for immune responses against blood-borne pathogens e.g. sepsis and malaria (this is the site where blood is filtered therefore it is a good site for the initiation of immune responses)

Lymph nodes - Located along lymphatic vessels. Lymph fluid from blood and tissue is filtered. Site of initiation of immune responses.

Mucosal lymphatic tissues especially tonsils in the nasopharynx and peyer’s patches in the intestines

Question 9

Lymphatic vessels, lymph fluid and lymph node

Answer 9

Lymph is the fluid that flows through the lymphatic system, a system composed of lymph vessels (channels) and intervening lymph nodes whose function, like the venous system, is to return fluid from the tissues to the central circulation.

Lymph nodes are small glands that filter lymph, the clear fluid that circulates through the lymphatic system. They become swollen in response to infection and tumours. Lymphatic fluid circulates through the lymphatic system, which is made of channels throughout your body that are similar to blood vessels.

Question 10

Difference between primary and secondary lymphoid organ

Answer 10

Primary = production of white blood cells/lymphocytes(type of WBC)/leukocytes (Bone marrow and Thymus)

Secondary = sites where immune responses are initiated (spleen and lymph nodes)

Question 11

Bone marrow and thymus

Answer 11

Primary lymphoid organs = production of white blood cells/lymphoctyes

Question 12

Spleen and lymphnodes

Answer 12

Secondary lymphoid organs = sites where immune responses are initiated

Question 13

Lymphatic system

Answer 13

Important for shuttling cells from one part of the body to another

The lymphatic system, or lymphoid system, is an organ system in vertebrates that is part of the circulatory system and the immune system. It is made up of a large network of lymphatic vessels, lymphatic or lymphoid organs, and lymphoid tissues. The vessels carry a clear fluid called lymph towards the heart

Question 14

3 layers of defence

Answer 14

First layer of defence - Chemical and physical barriers (prevent invaders from coming in however some things can get through)
Second layer - Innate arm (fast but not very specific arm of the immune systems - sometimes some microbes can still get through)
Third layer - Adaptive arm (really specific)

Question 15

Physical barrier - the skin

Answer 15

Epidermis - dead cells, keratin and phagocytic cells
Dermis - Thick layer of connective tissues, collagen and blood vessels and phagocytic immune cells

There is constant renewal of the outer layer by the inner layers (we shed dead skin cells every day)

Dendritic cells (immune cells) in this layer - the big arms of these cells reach out and grab things that are in the environment and take them back to the lymph node where they can activate the adaptive immune system. These cells are within the epidermis and are critical for initiating the adaptive immune cells.

Question 16

What is the top layer of skin called?
What is the layer of skin under this top layer?
What cells inhabit the skin layers?

Answer 16

Epidermis
Dermis
Dendritic cells

Question 17

Chemical defences of the skin

Answer 17

Antimicrobial peptides e.g. skin ‘defensins’ - form pores in microbial cell membranes (if microbe gets a pore in its membrane then it leeches out its contents and dies)

Lysozyme - breaks down bacterial cell walls which therefore causes destruction of the bacteria (enzyme)

Sebum - low pH (produced in the sebaceous glands that are associated with hair follicles therefore you won’t produce it on the palms of your hand because no hairs are there but produced in areas of the body that does have hair) (makes it an acidic environment which is very uncomfortable for pathogens to live in)

Salt - hypertonic (sweat glands produce very salty sweat, salt is hypertonic meaning that there is greater concentration of solutes outside of the cells than inside the cell and the type of cell we are talking about is a bacterial cell therefore bacteria’s water starts leeching out of the cell which dehydrates it and therefore it dies

Question 18

Mucous membranes

Answer 18

This is alive (this is how it differs from skin because skin is dead)

Composed of 1-2 layers
The outer layer of the mucous membrane is an epithelial layer - tightly packed live cells, constantly renewed, mucus-producing goblet cells

Mucus producing goblet cells - mucus comes out of the goblet cells and produces a layer over the top of an epithelial layer which is very protective and works to trap organisms and has lots of enzymes and molecules that are able to kill microbes (traps and kills)

Question 19

Where are the mucosal membranes?

Answer 19

Eyes (ocular), respiratory, oral, gastrointestinal system, urogenial/rectal

Mucous membranes line many tracts and structures of the body, including the mouth, nose, eyelids, trachea (windpipe) and lungs, stomach and intestines, and the ureters, urethra, and urinary bladder.

PPE protects mucosal sites

Question 20

Mucociliary escalator

Answer 20

Term for the apparatus of mucus and cilia; responsible for movement of mucus up and out of the respiratory tract; mucus traps particles and cilia propel mucus up and out of the lungs.

Cilia move mucus up the pharynx and this means that anything that was inhaled is coughed up or swallowed.

Because the cells are alive in the mucosal layer, it does create a bit more vulnerability therefore mucus layer is present for a little bit more protection

Present in the respiratory tract

The goblet cells keep the mucosal layer replenished

Question 21

Cilia in the mucociliary escalator

Answer 21

beat in a well organised manor, to move the mucus (containing trapped particles) – in the nose down to the throat; in the bronchi and trachea (windpipe), up to the throat

Question 22

Chemical defences of mucosal surfaces

Answer 22

Stomach - low pH (very acidic therefore hard for microbes to grow here)
Gall bladder - bile (very inhibitory for bacterium)
Intestine - digestive enzymes (attack and breakdown microbes)
Mucus
Defensins (form pores in the microbial cell membranes)
Lysozymes (in tears and urine - produce enzymes that are able to break down cell walls like the lysozyme)

Question 23

Skin vs mucous membranes

Answer 23

Skin 
Many cell layers 
Tightly packed cells 
Out layer of cells are dead and inner layers alive 
No mucus present 
There are lysosyme and denfensins present 
There is sebum present 
There are no cilia present 

Mucus
1 to a few cell layers
Tightly packed cells
Cells are alive
There is mucus present
In some cases there are lysosyme and defensins present
There is no sebum present (because there is no hair in these membranes)
There is cilia present in the trachea and uterine tubes

Question 24

Two arms of the immune system

Answer 24

Innate immunity 
Already in place 
Rapid (hours) 
Fixed 
Limited specificities 
Has no specific memory 

Adaptive immunity 
Improves during the response 
Slow (days to weeks) 
Variable 
Highly specific 
Has long-term specific memory (we exploit this in vaccinations)

Question 25

Innate immunity

Answer 25

Already in place
Rapid (hours)
Fixed (doesn’t change specificity during the response)
Limited specificities (detects molecular components shared by many pathogens known as PAMPs therefore they are no very good at telling one virus from another)
Has no specific memory

Innate immunity refers to nonspecific defense mechanisms that come into play immediately or within hours of an antigen’s appearance in the body. These mechanisms include physical barriers such as skin, chemicals in the blood, and immune system cells that attack foreign cells in the body.

Question 26

Adaptive immunity

Answer 26

Improves during the response
Slow (days to weeks)
Variable ( there is lots of variability in T and B cells therefore can recognise lots of different things)
Highly specific (detects molecular components specific to individual pathogens therefore can recognise a particular strain of a virus) 🦠
Has long-term specific memory (we exploit this in vaccinations) ( able to recall when it has been exposed to a particular virus - if you encounter the virus again then you won’t get the disease)

The adaptive immune system, also referred as the acquired immune system, is a subsystem of the immune system that is composed of specialized, systemic cells and processes that eliminates pathogens by preventing their growth.

Question 27

Autoimmune disease

Answer 27

Immune system reacting against our own body // An autoimmune disease is a condition in which your immune system mistakenly attacks your body.

Question 28

Lymphocytes vs leukocytes

Answer 28

leukocytes is the scientific name for all white blood cells and lymphocytesare a subtype of leukocyte.

Question 29

Humoral immunity and cellular immunity

Answer 29

Humoral
B cells
Adaptive immune system

Cellular
T cells
Adaptive immune system

Cell-mediated immune responses involve the destruction of infected cells by cytotoxic T cells, or the destruction of intracellular pathogens by macrophages

Humoral immunity is also called antibody-mediated immunity. With assistance from helper T cells, B cells will differentiate into plasma B cells that can produce antibodies against a specific antigen

Question 30

Surface barriers

Answer 30

Skin
Mucus membranes

Innate immune system

When microbiological organisms penetrate these external barriers, several other internal defence mechanisms are activated

Question 31

Internal defences

Answer 31

Innate immune system

Phagocytes 
Natural killer cells 
Inflammation 
Antimicrobial proteins 
Fever