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Y1 Fwong MCD Immunology (A) > 1 Introduction To Immunology > Flashcards

1 Introduction To Immunology Flashcards

1
Q

Q: What is the purpose of the immune system? Why is it important?

A

A: The environment is full of microorganisms - the immune system is a complex cellular and protein network that has evolved to protect the host from pathogenic microbes.

Tissue damage is also recognised by cells of the immune system

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2
Q

Q: What does the failure of the immune system lead to?

A

A: increased susceptibility to infection and sometimes cancer.

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3
Q

Q: When the regulation of the immune system becomes unbalanced, what can it lead to?

A

A: autoimmune disease and allergy.

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4
Q

Q: What is tissue repair?

A

A: type of HOMEOSTASIS

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5
Q

Q: What process relies on tissue damage being recognised by the immune system?

A

A: tissue repair

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6
Q

Q: What is the normal function of the immune system? (2)

A

A: Identify and eliminate harmful microorganisms and harmful substances such as toxins:
By distinguishing self from non-self proteins
AND
By identifying danger signals

Strike a balance between clearing the pathogen and causing collateral damage to the host - immunopathology

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7
Q

Q: Is distinguishing self from non-self proteins enough to trigger an immune response? Why?

A

A: no

you need to identify danger signals - there must be some secondary danger of inflammatory signal

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8
Q

Q: What reproduces faster, virus or bacteria?

A

A: Bacteria

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9
Q

Q: Describe the evolutionary arms race between pathogen and host.

A

A: The pathogen exerts selection on the host and the host exerts selection on the pathogen.

The pathogen reproduces much faster than the host and hence can evolve faster.

Therefore, the host relies on a flexible and rapid immune response.

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10
Q

Q: Which human genes are involved in the immune system?

A

A: Our most polymorphic genes - HLA, KIR- this variation has been selected for by exposure of populations to infectious disease.

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11
Q

Q: Summarise the time-course of a primary immune response to a virus with a diagram.

A

A: The initial response is the innate immune response.

Early peak of type 1 interferon (interferes with the replication of the virus)
Peak in NK cells (can recognise infected cells and lyse them)
These responses help to flatten out virus replication.

To eliminate the virus you need more specific immune responses from the adaptive immune system - this takes a little more time.

Rise in Cytotoxic T Lymphocytes (recognise and lyse infected cells)
CTLs start producing antibodies against the virus

Graph: days after viral infection against magnitude of response with lines for: type 1 interferon (alpha and beta)= peak day 2, natural killer (NK) cells= peak day 4, cytotoxic T lymphocytes (CTLs)=plateaus day 7/8, antibody, (virus titer)

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12
Q

Q: What is the primary response?

A

A: the first time the host has seen this particular virus

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13
Q

Q: Describe the innate immune response. When is it present from? What does it rely on? When the infection occurs, are the components ready? What’s the range for specificity? Which type of molecular patterns does it recognise?

A

A: Present from birth

Relies on pre-formed and rapidly synthesised components

If an infection happens, the components are already there to deal with it.

Limited specificity (non antigen specific)

Only recognises molecular patterns to do with danger.

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14
Q

Q: Describe the acquired/adapted immune response. When is it acquired? What does it depend on? Is it specific or non specific?

A

A: Acquired after exposure to the pathogen- Gives immunological memory

Depends on CLONAL SELECTION

Slow - takes days

Antigen Specific

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15
Q

Q: What is clonal selection?

A

A: selection of appropriate lymphocyte to fight the pathogen

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16
Q

Q: What is clonal expansion?

A

A: expansion of the clone of lymphocytes which recognises the particular pathogen

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17
Q

Q: What are examples of anatomical barriers for innate immunity? (3)

A

A: Skin

Mucus - trapping microbes

Cilial propulsion on epithelia

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18
Q

Q: What are examples of physiological barriers for innate immunity? (5)

A

A: Low pH

Secretion of lysozyme

Interferons

Anti-microbial peptides

complement

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19
Q

Q: When do antibodies develop?

A

A: don’t develop until you’ve been exposed to the pathogen so it’s totally part of acquired immunity

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20
Q

Q: What triggers the innate immune response?

A

A: Pathogens have various molecular structures which aren’t present on normal cells - the immune system can take advantage of these differences and respond to these patterns.

-Pathogen Associated Molecular Patterns PAMPs (E.g. dsRNA in cytoplasm, bacterial cell wall components) ->
Pattern-recognition Receptor = TLRs (Toll-like receptors)

-Danger Associated Molecular Patterns DAMPs (E.g. Monosodium urate, high extracellular [ATP], reactive oxygen species) -> Pattern-recognition Receptors = NLRs - NOD-like receptors, RLRs - RIG-I-like receptors, AIM2

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21
Q

Q: Why is high extracellular [ATP] a sign of danger?

A

A: because ATP isn’t useful outside cells.

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22
Q

Q: What does the innate immune response do?

A

A: Destroys invading nucleic acids (e.g. viruses) in the cytoplasm

Activates interleukins which, in turn, activate inflammatory pathways

Evokes type 1 interferons - bind to receptors on nearby cells and induces an antiviral state. Main consequences: Suppresses pathogen replication, buys time, kick starts the acquired immune response

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23
Q

Q: What is the acute phase inflammatory response?

A

A: innate response to tissue damage

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24
Q

Q: What does the acute phase inflammatory response involve?

A

A: Fever - indicative of acute phase inflammatory response (This is triggered by activation of interleukin-1)

Followed by production of acute phase proteins

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25
Q

Q: What are 3 acute phase proteins?

A

A: C-reactive protein, Serum amyloid protein, Mannan-binding lectin

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26
Q

Q: What are acute phase proteins?

A

A: soluble pattern recognition receptors

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27
Q

Q: Where are acute phase proteins produced?

A

A: liver

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28
Q

Q: What do the acute phase proteins do? Describe each one.

A

A: C-reactive protein and serum amyloid protein - bind to molecules found on the cell wall of some bacteria and fungi.

Mannan-binding lectin - binds to mannose sugar molecules which are not often found in mammalian cells.

Once these proteins are bound, phagocytes have receptors which can recognise these proteins and proceed to ingest the infectious agent.

binding can also trigger responses - it helps activate the complement system

29
Q

Q: Describe cytokines. What causes a cell to produce them?

A

A: Large family of soluble molecules - they are proteins that transmit information between cells

Some sort of stimulus will make a cell produce cytokines

30
Q

Q: Which protein is important in the proliferation of lymphocytes?

A

A: cytokines

31
Q

Q: How do cytokines act?

A

A: diffuse to nearby cells, bind to specific receptors and send a signal to the cell to alter the pathogen gene expression. Proteins will either be upregulated or downregulated leading to the biological effect

32
Q

Q: 3 examples of granular leukocytes?

A

A: Natural Killer (NK) Cells, Macrophages, Granulocytes (3 types)

33
Q

Q: What are natural killer (NK) cells? What do they do? What percentage of lymphocytes do they make?

A

A: Type of cytotoxic lymphocyte
Identify and kill virus-infected cells and tumour cells
10% of lymphocytes

34
Q

Q: What are macrophages? What do they do?

A

A: Mononuclear phagocytes, Release cytokines as signals of danger

35
Q

Q: What are the 3 types of granulocytes? What do they do? What percentage of circulating WBCs? Phagocytic?

A

A: Basophils- Least abundant type of granulocyte, Not phagocytic, Release histamines, <1% of circulating WBCs

Neutrophils- Also called polymorphonuclear neutrophils (PMN), Nucleus is multi-lobed, 50-70% of circulating WBCs, Phagocytic

Eosinophils- Bi-lobed nucleus, Important in immune response to parasites, 1-3% of circulating WBCs

36
Q

Q: Define antigen.

A

A: a molecule that reacts with antibodies or T cells

37
Q

Q: Define antibody.

A

A: an immunoglobulin molecule in the blood and body fluids which binds specifically to an antigen

38
Q

Q: Define an immunogen.

A

A: antigens that initiate an immune response

39
Q

Q: What are the 5 classes of immunoglobulins?

A

A: all are a class of proteins

IgG

IgM

IgA

IgE

IgD

40
Q

Q: What are IgG? What percentage do they make up of serum Ig? Length of half life?

Which response are they part of?

A 
A: Monomeric antibody
75% of serum Ig 
Long half life in serum 
Crosses the placenta from mother to foetus to give the new born immunity against infection.  
Part of secondary immune response
41
Q

Q: What are IgM? What percentage do they make up of serum Ig? What shape are they? How many binding sites does it have? What are they good at? What response are they important in?

A 
A: 10% of serum Ig 
Pentamer - star shaped
Multivalent antibody - 10 binding sites 
Good at agglutinating (clumping together) pathogens
Important in primary immune response
42
Q

Q: What are IgA? What are they found in? What do they contain- what does this do?

A

A: Dimer Found in body secretions (mucosal surfaces)
Contains secretory .component - protects it from degradation on mucosal surfaces which usually have proteases present (hostile environment)

43
Q

Q: What are IgE involved in? How do they act?

A

A: Involved in allergic responses

Binds to basophils and mast cells and triggers the release of histamines.

44
Q

Q: What percentage do IgD make up of serum Ig? What are they involved in?

A

A: Very low concentration in serum

Predominantly involved in membrane bound form on B lymphocytes in signalling

45
Q

Q: How does an antibody recognise an antigen?

A

A:

that antibody’s binding site makes a perfect fit with a region (EPITOPE) on the antigen.

46
Q

Q: What is the epitope of the antigen?

A

A: the part of the antigen that is bound by the antibody

47
Q

Q: What are the 4 mechanisms that an antibody kills a virus?

A

A: Binds to virus - prevents attachment to cell

Opsonisation - virus is coated in antibody so it can be more easily phagocytosed.

Complement - mediated lysis of membrane bound virus

Antibody-Dependent Cell-Mediated Cytotoxicity (ADCC) - mediated by NK-like cells - if the cell is infected, there will be viral proteins in the membrane - the cell becomes coated with antibody - NK cells have receptors which can recognise these antibodies and lyse the infected cells.

48
Q

Q: What are the cells of the acquired immune system?

A

A: Lymphocytes - agranular leukocytes (majority are in the lymph)

T-cell = Thymus derived 
B-cell = Bone marrow derived

There are many subtypes of these molecules which are distinguished by CD markers

49
Q

Q: What are the 3 types of antigen-specific lymphocytes?

A

A: B cell (humoural)

Helper T-cell

Cytotoxic T-cell (CTL)

50
Q

Q: What is active immunity?

A

A: the type of immunity that is actively developed in an individual in response to a pathogen or vaccination - it is an acquired response to the antigen

51
Q

Q: What is passive immunity? Give an example.

A

A: the transfer of pre-formed antibodies into a person to give them defence against a pathogen
IgG from mother to baby gives the baby passive immunity

52
Q

Q: What is the difference between the primary and secondary immune response?

A

A: Secondary = subsequent exposure to the same pathogen

Secondary Response - BIGGER response + FASTER

53
Q

Q: How do the B cell and T cell antigen receptors differ?

A

A: B-cell antigen receptor is a membrane bound antibody- These bind INTACT antigens

There are 2 protein chains (a and b) which together make the T cell antigen receptor (TCR) - These only bind DIGESTED (PROCESSED) antigen fragments

54
Q

Q: How does the TCR recognise an antigen?

A

A: TCR recognises a complex of: Antigen Peptide + HLA (MHC) Molecule

55
Q

Q: What is the MHC?

A

A: Major Histocompatibility Complex - these molecules present processed antigens to T lymphocytes

The MHC is humans is also known as the HLA (Human Leukocyte Antigen)

56
Q

Q: How is clonal diversity generated in humans?

A

A: During B and T cell development - RANDOM GENETIC RECOMBINATIONS take place within each cell among multiple copies of:

B cells - Immunoglobulin gene segments
T cells - TCR gene segments

-> end up with a very large repertoire of different receptors which can respond to a large variety of antigens

57
Q

Q: Describe the clonal nature of the adaptive immune response?

A

A: Each lymphocyte carries a single, unique antigen receptor

There are millions of lymphocytes, hence, millions of different antigen receptors in the body.

Lymphocytes which have a binding site that is complementary to an antigen will proliferate and survive.

The majority of lymphocyte clones die out.

58
Q

Q: What are naïve lymphocytes?

A

A: lymphocytes which have never come into contact with their antigen before

59
Q

Q: Where are the majority of T cells circulating?

A

A: 98% in lymph

60
Q

Q: What causes selective expansion of a clone of a T or B cell?

A

A: antigen will bind to the surface receptors on the B cell (Ig) or T cell (TCR)

61
Q

Q: What happens to lymphocytes that have proliferated during the primary immune response?

A

A: Most will DIE after fulfilling their function

Some lymphocytes survive as memory cells

62
Q

Q: How does the immune system clear the pathogen during the primary immune response?

A

A: Cytotoxic T Lymphocytes (CTLs) kill infected cells by injecting lethal enzymes

Antibodies bind to the pathogen and direct phagocytes to come and ingest them

63
Q

Q: Summarise using a flow diagram the primary immune response in terms of lymphocytes.

A

A: antigen
|
\ /
Naïve lymphocytes (polyclonal) ———–> activation -> clonal expansion -> effector lymphocytes

64
Q

Q: What is the role of a APC? How do they form?

A

A: transport the antigens from the tissues into secondary lymphoid organs

Antigens meet T cells in secondary lymphoid organs

Antigen-presenting cells capture, process and present antigens to T lymphocytes

APCs are good at activating T cell responses- Immune response

65
Q

Q: How is the lymphatic system organised?

A

A: Lymphatic Vessels: Venules, Veins, Ducts

Lymphatic Tissues: Nodules, Nodes, Tonsils, Peyer’s Patches

Lymphatic Organ: Spleen, Thymus

66
Q

Q:What does the lymphatic system do to aid immune responses?

A

A: The lymphatic system drains the fluid to look for antigens - it is filtered through lymph nodes where T lymphocytes have the chance to interact with antigens

67
Q

Q: Are innate or acquired responses faster?

A

A: innate

68
Q

Q: What does immunological memory forms the basis of?

A

A: vaccination

69
Q

Q: Draw a diagram showing the cells and humoral factors involved in innate and acquired immunity.

A

A:

cells:
innate- neutrophils, NK cells
both- macrophages, monocytes, dendritic cells, mast cells
adaptive- macrophages

soluble factors:
innate- antimicrobial peptides
both- complement, cytokines
adaptive- antibodies

Y1 Fwong MCD Immunology (A) (9 decks)

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