Immunology 1- Introduction to the immune system

Question 1

What does the immune system need to do to function

Answer 1

Detect there is a “threat”

Respond effectively against the “threat”

Minimise “collateral damage”, return to healthy self

If necessary, remember the “threat” to respond more
effectively if it is met again

Question 2

What is meant by immunology

Answer 2

The study of physiological mechanisms that we use to defend our bodies against invasion from other organisms, primarily microorganisms. The immune system is crucial to human survival, in patients with immunodeficiencies, even minor infections can be fatal, can also increase susceptibility to cancer.

Question 3

Why is knowledge of the immune system important

Answer 3

Allows its manipulation to improve human health i.e vaccines, immunotherapy, diagnosis (levels of antibodies).

Question 4

What is the immune system

Answer 4

Complex cellular and protein network that has evolved to protect the host from pathogenic microbes

Question 5

What are the consequences of an abnormal immune response

Answer 5

Abnormal function or regulation of the immune system may lead to disease, e.g. autoimmune diseases, allergy

Question 6

Why is it important that the immune system has a healing role too

Answer 6

The immune system has powerful defence mechanisms, which can destroy our own cells, hence need to play a healing role too. Hence the immune system is Also involved in homeostasis e.g. tissue repair

Question 7

How does the immune system identify and eliminate harmful microorganisms and harmful substances such as toxins.

Answer 7

by distinguishing ‘self’ from ‘non-self’ (sometimes ‘normal self’ from ‘abnormal self’ in cancer)
and
by identifying ‘danger’ signals, including tissue damage

Question 8

Can the immune system have receptors for neurotransmitters

Answer 8

Yes

Question 9

How can the immune system be described as a sensory system

Answer 9

Stress and food can effect the immune system, but the immune system is not a separate entity,
but is fully integrated into other body systems, hence it is described as a sensory system that can move.

Question 10

What is meant by immunopathology

Answer 10

Damage to cells caused by the mechanisms of the immune system- often collateral damage in the immune response to a foreign antigen.

Question 11

What is the importance of the danger signal in an immune response

Answer 11

Only immune responses initiated against appropriate non-self antigens, this means it will not respond to the antigens expressed on the surface of food molecules for example.

Question 12

Can the immune system respond to tissue damage in the absence of infection

Answer 12

Yes

Question 13

Describe the evolutionary arms race between humans and bacteria,

Answer 13

The host exerts selection on the pathogen; the pathogen exerts selection on the host Only humans with effective immune systems will survive, only bacteria that can invade human tissue effectively will survive.

Question 14

What are the consequences of the evolutionary arms race between humans and pathogens

Answer 14

The pathogen replicates millions of times faster than the host - and so can evolve faster

The host therefore relies on a flexible and rapid immune response

Our most polymorphic (variable) genes are those that control the immune response: this variation has been
selected for by exposure of populations to infectious diseases

Question 15

What are the two strategies used by immune system cells to recognise foreign antigens

Answer 15

Strategy 1
Recognise molecular patterns- could be carbohydrates found on pathogens
Hundreds of receptors
Germ-line encoded

Strategy 2
Recognise precise structure
Millions of receptors
Generated by random recombination of gene segments

Question 16

Why do we need to utilise recombination of gene segments to produce different receptors that recognise different antigens

Answer 16

Limited number of germ-line encoded receptors in each individual to recognise all the foreign antigens, would be impossible to have millions of genes coding for each specific receptor.

Question 17

What are the advantages of germ-line codes receptors

Answer 17

Many cells can express the same
receptor, allowing a rapid, effective
response.

Limited receptor diversity, some pathogens
may not be efficiently recognised.

Question 18

What are the advantages and disadvantages of having receptors encoded by the random recombination of gene segments

Answer 18

Initially very few cells express a specific
receptor, so they must be greatly expanded
to generate an effective response. This
takes time.

Massive diversity of receptors, all structures
may potentially be recognised. However,
because of random nature of receptor 
generation, there is potential for 
autoimmunity.

Question 19

Why is it important that lymphocytes are tightly regulated

Answer 19

Due to the nature of the recombination process, the receptors generated have the potential to recognise self-tissue, hence the production of lymphocytes must be tightly regulated to avoid autoimmunity.

Question 20

What are the two types of ‘triggers’ recognised by Pattern Recognition Receptors

Answer 20

PAMPs – Pathogen-Associated Molecular Patterns

DAMPs – Damage-Associated Molecular Patterns- from normal self-patterns- release of their contents- ATP, DNA, heat shock proteins such as uric acid and fragments of the ECM ( especially galectins)- act as receptors for PRRs.

Question 21

Give examples of PAMPs on bacteria

Answer 21

Flagellin, LPS, Proteoglycan

Question 22

Give examples of PAMPs found on viruses

Answer 22

Envelope glycoproteins, unmethylated CpG motifs, ssRNA, dsRNA

Question 23

Give examples of PAMPs found on fungi

Answer 23

Mannoproteins (cell wall), Phosphlipomannans, Beta Glucans (sugar found in cell wall), Unmethylated CpG motifs

Question 24

Give examples of PAMPs found on parasites

Answer 24

profilin- actin-binding molecule, glycolipids, DNA.

Question 25

Describe the difference between T cell and B cell antigen receptors

Answer 25

The B cell antigen receptor is a membrane-bound antibody - binds intact antigens - found in the humour Expressed on the T cell surface are 2 protein chains (α and β) which together make the T cell receptor (TCR) - binds ‘processed’ antigen fragments presented at cell surfaces

Question 26

Which part of the antigen does the antigen receptor bind to

Answer 26

the epitope

Question 27

What does each clone of B cell and T cell carry

Answer 27

Each clone of B cells or T cells has a unique receptor, specific to one antigen; each cell carries many copies of this receptor on the cell surface.

Question 28

Describe the characteristics of innate immunity

Answer 28

independent of previous exposure broad specificity depends on pre-formed and rapidly synthesised components fast (starts in minutes/hours) limited specificity – pattern recognition of ‘danger signals’

Question 29

Describe the characteristics of adaptive immunity

Answer 29

an adaptation to exposure (also called acquired immunity) depends on clonal selection: i.e. expansion of cells or antibodies, selected for antigen specificity slow (starts in days) highly specific to foreign antigens

Question 30

What is the basic role of interferons

Answer 30

To interfere with pathogen functions.

Question 31

What is the purpose of the innate immune response

Answer 31

destroys invading nucleic acids (e.g. viruses) in the cytoplasm activates inflammatory pathways, signals for recruitment of immune system cells to sites of damage/infection elicits type 1 interferons, for anti-viral defence two main consequences: “buys time” while the adaptive immune response starts promotes and directs the appropriate adaptive immune response

Question 32

What are the effector arms used by the adaptive immune system

Answer 32

Cellular immunity T and B lymphocytes Humoral immunity antibodies

Question 33

What are the cells of the adaptive immune system

Answer 33

Lymphocytes (agranular leukocytes) 20-40% of the circulating WBCs, 99% of the cells in lymph - T (Thymus-derived) cells - B (Bone marrow-derived) cells Each subset has distinct cell-surface molecules e.g. CD4 on helper T-cell Basophils, mast cells, dendritic cells, Natural Killer Cells

Question 34

What are the cells of the innate response

Answer 34

Neutrophils, eosinophils, macrophages, basophils, mast cells, dendritic cells, Natural Killer cells

Question 35

What are the soluble factors used by the adaptive response

Answer 35

Cytokines and antibodies

Question 36

What are the soluble factors utilised by the innate response

Answer 36

Acute phase proteins Complement Cytokines

Question 37

Describe the generation of clonal diversity in B and T lymphocytes

Answer 37

During B and T cell development, random genetic recombinations occur within each cell among multiple copies of immunoglobulin gene segments (B cells) or TCR gene segments (T cells). =strategy 2. These processes generate the diversity of clones of lymphocytes: each clone is specific to a different antigen.

Question 38

Describe the consequences of the clonal diversity in the adaptive immune response

Answer 38

Each lymphocyte carries a single, unique antigen receptor. There are millions of lymphocytes in the body, and thus millions of different antigen receptors. Lymphocytes that meet an antigen they recognize will proliferate and survive. The huge majority of lymphocyte clones will die out.

Question 39

Describe the process of clonal selection

Answer 39

A typical antigen is recognized by 1 in ~105 naive T cells. 98% of T cells are in the lymph circulation and organs; 2% in blood Antigen binds to surface receptor on the B cell or the T cell and causes selective expansion of that clone = clonal selection Effector lymphocytes are produced which bind to complementary antigens to eliminate the infection.

Question 40

What happens when the antigen is removed from the body

Answer 40

Most lymphocytes that have proliferated recently will die after fulfilling their function Some survive as memory cells: this forms the basis of vaccination Re-exposure to a previously encountered antigen leads to a more rapid and greater immune response (secondary response)

Question 41

What are antigens

Answer 41

molecules that react with and are bound by antibodies or T cells. However, not all antigens can induce an immune response in the host, those that can are termed immunogens.

Question 42

What are antibodies

Answer 42

immunoglobulins found in the blood and body fluids, produced in response to foreign antigen and bind specifically to the foreign antigen. They are an adaptive component of the humoral (soluble, non-cellular) immune response.

Question 43

What are lymphocytes

Answer 43

Mononuclear cells that are part of the leukocyte lineage, named as they are the main cell type found in the lymph. All cells of the immune system are derived from stem cells in the bone marrow.

Question 44

What is meant by naïve lymphocytes

Answer 44

lymphocytes that have never encountered the antigen complementary to their cell surface receptor, and thus have never responded to it.

Question 45

What is the purpose of memory lymphocytes

Answer 45

Product of an immune response, ensuring that the specificity of their antigen receptor remains in the pool of lymphocytes in the body.

Question 46

What is active immunity

Answer 46

The induction of an immune response within an individual by the introduction of an antigen.

Question 47

What is passive immunity

Answer 47

immunity gained without antigen induction of a response i.e by a transfer of antibody, immune serum, or activated lymphocytes into a naïve recipient.

Question 48

What is meant by the primary response

Answer 48

response made by naïve lymphocytes when they first encounter their specific antigen.

Question 49

What is meant by the secondary response

Answer 49

response made by memory lymphocytes, when they re-encounter their specific antigen.

Question 50

What happens to the lymphocytes that do not encounter their specific antigen

Answer 50

They die. the overall size of the total peripheral lymphoid pool is regulated by homeostatic mechanisms.

Question 51

Which lymphoid tissue are antigens which present in the blood taken to

Answer 51

The spleen.

Question 52

Describe the importance of the organisation of the immune system

Answer 52

The physiological organisation of the immune system is important to its function. The physical organisation is essential to allow adaptive responses against danger anywhere within the body. The lymphatic system drains fluid from tissue cells via lymph nodes, through which lymphocytes recirculate. The tissues are patrolled by lymphocytes, antibodies and antigen-presenting cells.

Question 53

Which responses does gut-associated lymphoid tissue control

Answer 53

Responses in the intestinal tract.

Question 54

What is the first line of defence

Answer 54

The innate immune system

Question 55

What does clonally distributed mean

Answer 55

That unique receptors are found on each lymphocyte.