Tutorial 8 - immune system

Question 1

What are the 2 kinds of disease resistance of the immune system?

Answer 1

1. Nonspecific resistance (innate immunity)
   - Present at birth ad includes defence mechanisms that provide general protection against invasion by a wide range of pathogens
2. Immunity (adaptive immunity)
   - Involves activation of specific lymphocytes that combat a particular pathogen or other foreign substance
3. The body system that carries out immune responses is the lymphatic system

Question 2

What are the functions of the lymphatic system?

Answer 2

1. drain interstitial fluid
2. transport dietary fats
3. carry out immune responses

Question 3

Define innate immunity

Answer 3

1. innate immunity refers to a wide variety of body responses that serve to protect us against invasion of a wide variety of pathogens and their toxins
2. We are born with this kind of immunity

Question 4

Define the two lines of defence (immunity)

Answer 4

1. physical barrier:
   - skin, sweat and sebaceous glands, mucous membranes, tears and saliva, gastric acid, acidic urine, normal flora.
2. general defence: (immune cells or substances that treat all foreign cells in much the same way)
   - Phagocytes (neutrophils, macrophages)
   - NK (natural killer) cells (immunological surveillance)
   - Interferons (proteins released from virally infected cells) – protect nearby cells from viral entry
   - Complement proteins – cascade effect that destroys target cell membranes, promotes inflammation & attracts phagocytosis
   - inflammation
   - fever

Question 5

Define the five types of white blood cells and their functions

Answer 5

1. Neutrophils (50 - 70% of WBCs) short-lived cells that phagocytose bacteria
2. Lymphocytes (T & B) (20 - 40% of WBCs) - mostly found in lymphoid tissues - specific immune response
3. Monocytes (become macrophages in tissues) (2 - 8% of WBCs) - less abundant than neutrophils but longer-lived
4. Eosinophils (1-4% of WBCs) - attack parasitic worms, involved in allergy & asthma (IgE system)
5. Basophils (0.1% of WBCs) release histamine & heparin, involved in inflammatory response, not phagocytic

Question 6

inflammation

Answer 6

1. Inflammation is a non-specific localised tissue response to tissue damage which has occurred through injury or infection. Damaged cells release chemicals such as prostaglandins, histamine, bradykinins, serotonin and complement, which initiate the inflammatory response.
2. Think of it as “inflammatory soup” – the same molecules also trigger pain responses by sensitising or activating neurons

Question 7

What is the 4 signs and symptoms of inflammation and reasons for the them?

Answer 7

1. redness
   - due to vasodilation and increased blood supply to the area.
2. heat
   - due to increased blood supply to the area
3. swelling
   - or oedema, due to increased vascular permeability and accumulation of exudate (mass of cells and fluid that has seeped out of blood vessels or an organ)
4. pain
   - due to increased pressure on nerve endings from swelling/oedema & the “pain soup” – contents of cells (prostaglandins) which also trigger inflammation generally – activate and/or sensitise C-fibres (sensory/afferent pain neurons)

Question 8

Define adaptive immunity (specific immunity) and antigens

Answer 8

1. Adaptive immunity is the ability of the body to defend itself against specific invading agents. It has 2 types:
   - cell-mediated
   - antibody-mediated
2. antigens are proteins located at the surface of a cell or virus and are targeted by a specific immune response.

Question 9

how does the specific immune cells recognise and remember specific antigens

Answer 9

1. T Helper (CD4) cells recognise a specific antigen which is often ‘presented’ by antigen presenting cells - phagocytic cells such as macrophages.
2. Cytotoxic T (CD8) cells – stimulated by cytokines, recognise foreign antigens, kill virally infected & foreign cells.

Question 10

Define pathways of antigen processing/recognising (B cells/T cells)

Answer 10

For an adaptive immune response to occur, B cells and T cells must recognise that a foreign antigen is present.

• B cells can recognise and bind to antigens in lymph, interstitial fluid, or blood plasma
• T cells only recognise fragments of antigenic proteins that are processed and presented in a certain way

Question 11

specific immune cells and their functions

Answer 11

1. B lymphocytes become plasma cells which produce antibodies (humoral immunity) - directed against specific antigens in body fluids
2. T lymphocytes – for cell-mediated immunity, directed against intracellular antigens (e.g. antigens on viruses).
3. Sub-types:
   - T Helper (CD4) – control humoral immune response of B cells, produce interleukins and promote cell multiplication.
   - T Cytotoxic (CD8) - effector cells of cell mediated immunity, release lethal lytic chemicals that kill cells on contact.
   - T Suppressor cells - (CD8) damp down the immune response.

Question 12

the timeline associated with the specific immune system’s first exposure to an antigen

Answer 12

1. The primary immune response follows the first exposure to an antigen. It is a slow response that takes about 2 weeks.
2. Initially, small quantities of large multivalent IgM antibodies are typically produced.
   - IgM: the largest antibody and the first to arrive on the scene after initial exposure to antigen. Produced in the spleen.

Question 13

IgM antibodies

Answer 13

1. The most common type of antibody in the circulation. Created and released by plasma B cells and each has two antigen binding sites.
2. They protect the body from infections in a few ways:
   - IgG-mediated binding of pathogens causes their immobilization and binding together viaagglutination;
   - IgG coating of pathogen surfaces (opsonization) allows their recognition and ingestion byphagocytic immune cellsleading to the elimination of the pathogen itself;
   - IgG activates theclassical pathwayof thecomplement system, a cascade of immune protein production that results in pathogen elimination;
3. IgG also binds andneutralizestoxins;
4. IgG also plays an important role inantibody-dependent cell-mediated cytotoxicity(ADCC) andintracellular antibody-mediated proteolysis, in which it binds toTRIM21(the receptor with greatest affinity to IgG in humans) in order to direct marked virions (virus) to theproteasome(contains proteases to cleave proteins) in the cytosol;
5. IgG is also associated with type II and type IIIhypersensitivityreactions.

Question 14

The specific immune system responds to the second and all subsequent exposures to the same antigen

Answer 14

1. The secondary immune response occurs on the second and all subsequent exposures to the same antigen.
2. It is rapid and efficient, with specialised memory B and T cells becoming activated and generating large quantities of antibodies of the IgG type within 2-3 days of re-exposure.

Question 15

plasma cells and antibodies (immunoglobulins)

Answer 15

1. Activated B cells form clones of plasma cells which in turn produce specific antibodies.
2. The primary role of antibodies is to remove or inactivate the specific antigens by agglutination or clumping.

Question 16

antibody-mediated immunity

Answer 16

1. An antigen is recognised and bound
2. Helper T cells co-stimulate the B cell so the B cell can proliferate and differentiate into a clone of effector cells (plasma cells) that produce one specific antibody (at scale) against one specific antigen
3. The antigen is eliminated

Question 17

active versus passive immunity

Answer 17

1. Active immunity is long lasting immunity in which memory cells and antibodies are produced (naturally by infection, or by vaccination). and maintained in a latent state
2. Passive immunity is acquired by the transfer of antibodies from an immune person to a non-immune person (short lived as no memory cells develop and antibodies break down with time)

a. Treating patients with convalescent serum (passive immunity) has been used for over 100 years, and was used with Ebola, and currently being trialed with SARS-CoV-2.
b. Antibodies are passed to infant via colostrum, and some via placenta (passive immunity)

Question 18

Homeostatic imbalances: allergies

Answer 18

1. Allergies occur when a person is overly reactive to a substance that is well-tolerated by most others
2. When an allergic reaction occurs so does tissue damage
3. There are 4 types of hypersensitivity reactions, Type I-IV

Question 19

Homeostatic imbalances: autoimmune: diseases

Answer 19

An autoimmune disease occurs when the immune system fails to display self-tolerance and, instead, attacks the person’s own body tissue(s).

Question 20

Blood groups

Answer 20

Blood groups are based on the presence or absence of - A and B antigens on red blood cells.

1. A person with blood group A possesses the A antigen on his or her red blood cells.
   - A person who possesses the A antigen (blood group A) on his/her red blood cells produces anti-B antibodies.
2. A person with blood group B possesses the B antigen on his or her red blood cells.
   - A person who possesses the B antigen (blood group B) on his/her red blood cells produces anti-A antibodies.
3. A person with blood group AB possesses both the A antigen and the B antigen on his or her red blood cells.
   - A person who possesses both the A antigen and the B antigen (blood group AB) on his/her red blood cells produces no antibodies to the A and the B antigen.
4. A person with blood group O has neither the A antigen nor the B antigen on his or her red blood cells.
   - A person who has neither the A antigen nor the B antigen (blood group O) produces both anti-A antibodies and anti-B antibodies.

Question 21

Why blood group O is known as the ‘universal donor’?

Answer 21

Blood group O is known as the universal donor as it contains no A or B antigens. Transfusion reactions are due to mismatch with a donor’s antigens.

Question 22

Why is AB known as the ‘universal recipient’?

Answer 22

Blood group AB is known as the universal recipient as it produces no A or B antibodies.

Question 23

Define Rh factor (rhesus factor)

Answer 23

1. The red blood cells of humans also possess or do not possess another antigen, the D antigen. If a red blood cell possesses a D antigen that person is said to be Rh positive. If a red blood cell does not possess the D antigen that person is said to be Rh negative. Hence blood groups are known as O positive, B negative etc.
2. A person who does not possess the D antigen on his/her red blood cells produces anti-D antibodies only upon exposure to the D antigen (this is not common).

Question 24

Define haemolytic disease of the newborn

Answer 24

1. Occurs in the second pregnancy of a female who is Rh negative and carries an Rh positive foetus (for the second time).
2. Antibodies are able to cross the placenta from mother to foetus but blood cells cannot. However during the birth of the first Rh positive foetus carried by an Rh negative mother, the D antigen from the baby enters the mother’s blood and her specific immune system produces D antibodies within 2 weeks of birth.
3. During the next pregnancy with another Rh positive foetus the D antibodies (produced by the mother after the first exposure to the D antigen) cross the placenta and cause a transfusion reaction.
4. This situation is prevented by the injection of anti-D antibodies to Rh negative mothers immediately after delivery.

Question 25

Define ‘specificity’

Answer 25

Cells of the adaptive immune system see distinct “antigens” and will only respond to that antigen

Question 26

Define ‘diversity’

Answer 26

The adaptive immune system contains lots of different T and B cell clones that recognise lots of different antigens thus ensuring we can respond to all the antigens we may encounter

Question 27

Define ‘memory’

Answer 27

The ability of the cells of our adaptive immune system to “remember” a pathogen. It ensures that the 2nd response to the same pathogen is enhanced. This concept underpins the success of vaccination strategies.

Question 28

Define ‘clonal expansion’

Answer 28

1. Cells of the adaptive immune system have the capacity to divide and become a clonal army of cells, all specific for the one antigen/pathogen. Clonal expansion happens rapidly upon re-exposure to an antigen.
2. This concept also underpins the success of vaccination strategies.

Question 29

Define ‘specialisation’

Answer 29

Different cells of the adaptive immune system are optimised to combat different types of pathogens. For example, T cells kill virally infected cells, whereas antibodies from B cells protect us from infection by eliminating viruses before they can infect a cell.

Question 30

Define ‘contraction and homeostasis’

Answer 30

This is important when the pathogen has been contained as it allows space for the generation of new immune responses to other pathogens.

Question 31

Define ‘non-reactivity to self’

Answer 31

Cells of the adaptive immune system can differentiate between foreign and self. This ensures the survival of the host and prevents the development of potentially deadly autoimmune diseases.