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Molecules, Cells and Diseases (MCD) and Epidemiology in Practice (EiP) > Immunology > Flashcards

Immunology Flashcards

1
Q

Where are mast cells most commonly found?

A

The connective tissue (under the skin) and the epithelial mucosae (the respiratory and intestinal epithelia).

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2
Q

Which chemicals are secreted by mast cells when IgE binds to the cell surface?

A

Histamine and leukotrienes.

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3
Q

What are the effects of inflammatory mediators released by mast cells upon blood vessels and smooth muscle?

A

In connective tissue, vasodilation is caused, increasing blood flow near the surface of the skin and oedema. Around mucosae, smooth muscle constricts, causing constriction of the airways and intestinal walls.

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4
Q

What is urticaria?

A

A skin rash caused by an allergen. Stimulation of connective tissue mast cells causes vasodilation leading to the red colour of the rash, and oedema leading to its raised appearance.

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5
Q

What are the symptoms of a reaction to an inhaled allergen?

A

Stimulation of epithelia in the nose - leading to mucus secretion.
Contraction of smooth muscle of the bronchioles in the lungs, alongside inflammation and increased mucus secretion. This leads to difficulty breathing.

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6
Q

What are the symptoms of an allergen that is ingested?

A

Vomiting and diarrhoea due to constriction of smooth muscle lining the GI tract. If the allergen is absorbed and passes into the blood stream it may also cause skin symptoms.

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7
Q

What is anaphylaxis?

A

A SYSTEMIC response to an allergen causing immediate responses throughout the body.

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8
Q

List symptoms of anaphylaxis.

A

High RR and HR.
Nausea, abdominal cramps and/or diarrhoea.
Difficulty breathing.

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9
Q

Describe the emergency treatment given to someone undergoing an anaphylactic reaction.

A

First tackle hypotension –> then underlying inflammation
Lay them down with feet up to improve blood supply to head and torso. Inject adrenaline to constrict peripheral blood vessels. May need to control BP using IV.
Then administer antihistamines and anti-inflammatory corticosteroids.
If breathing problems persist oxygen may be required and bronchodilators given by inhaler.

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10
Q

What substances can cause anaphylaxis?

A

Ones which can pass freely throughout the body.
Penicillin (especially if previously given by IV), some other drugs (local anaesthetics and x-ray contrast agents), venom, peanuts.

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11
Q

Which 2 pattern recognition receptors (PRRs) does the innate immune system use?

A

PAMPs - pathogen-associated molecular patterns

DAMPs - damage-associated molecular patterns

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12
Q

Give 2 examples of PAMPs

A

Flagellin of bacteria, envelope glycoproteins of viruses

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13
Q

Give 2 examples of DAMPs

A

Extracellular ATP, heat shock proteins.

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14
Q

What are primary lymphoid organs?

A

Sites where lymphocytes are produced by lymphopoiesis (B and T lymphocytes)

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15
Q

What are secondary lymphoid organs and give 3 examples.

A

Sites where lymphocytes can interact with antigen and other lymphocytes.
Spleen; lymph nodes; mucosal associated lymphoid tissues (MALT).

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16
Q

Describe lymphocyte recirculation.

A

Naïve lymphocytes enter the blood from the primary lymphoid organs. The lymphocyte circulates through the peripheral lymphoid tissues. If it comes across its antigen being presented, it becomes activated. If not, it recirculates until death.

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17
Q

Describe the extravasation of naïve t-cells into lymph nodes from high endothelial venules (HEVs).

A

The t-lymphocytes roll along the wall of the HEV, adhering weakly by selectin. Integrin is a low-affinity binding form. When chemokine on epithelial cell surface binds to chemokine receptor on the lymphocyte, the integrin changes to a high-affinity binding form. Then lymphocyte then undergoes transendothelial migration. NEUTROPHILS also migrate into tissues by this mechanism.

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18
Q

Describe the structure of lymphocytes.

A

Small cells with agranular cytoplasm and large spherical nucleus.

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19
Q

What are cluster of differentiation (CD) markers?

A

Cell surface markers used to differentiate between cells of the haematopoietic system.

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20
Q

What are CD4+ cells?

A

Helper T-cell (regulatory function) - secrete cytokines.

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21
Q

What are CD8+ cells?

A

Cytotoxic T-cells which lyse infected cells.

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22
Q

What are antigen presenting cells (APCs) and give 3 examples.

A

Cells which can present processed antigens to T-lymphocytes to initiate an adaptive immune response.
Dendritic cells, B lymphocytes and activated macrophages

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23
Q

What do mast cells do?

A

Release granules (containing histamine and leukotriene) - pro-inflammatory.

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24
Q

What are the functions of monocytes/macrophages?

A

Phagocytosis, killing microbes, cytokine release, APCs.

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25
Q

What’s the function of eosinophils?

A

Defence against parasites.

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26
Q

What is opsonisation?

A

The coating of microbes with proteins (OPSONINS) to facilitate phagocytosis.

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27
Q

What are neutrophil extracellular traps (NETs)?

A

Activated neutrophils release granule proteins and chromatin to form extracellular fibres, trapping microbes. This enhances phagocytosis.

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28
Q

What’s the difference between monocytes and macrophages?

A

Monocytes circulate in the blood and become macrophages when they migrate into tissues.

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29
Q

How do macrophages function?

A

They express receptors for many different bacterial constituents. Binding stimulates the release of cytokines (alerting the immune system). They then engulf and destroy the bacterium.

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30
Q

How does vasodilation and increased vascular permeability (caused by mast cells) help the immune system?

A

Slows blood flow at the site of infection.

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31
Q

What are natural killer cells?

A

Large granulated lymphocytes. They lyse infected cells. They have receptors which bind to antibody-coated cells. Self recognition –> leave target alone. Missing self –> lyse target cells.

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32
Q

What are cytokines, their effects and characteristics?

A

They are small secreted proteins, used for cell to cell communication, generally acting locally. They have biological effects at low concentrations.

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33
Q

What are interleukins?

A

Cytokines used for communication between leukocytes.

34
Q

What are interferons?

A

Cytokines with antiviral effects.

35
Q

What are chemokines?

A

Cytokines used for cell movement (chemotaxis).

36
Q

What are growth factors?

A

Cytokines involved in cell differentiation and proliferation.

37
Q

Describe autocrine action.

A

Stimulus acts on a cell. Cell produces cytokine which then binds to a receptor on the surface of the same cell, resulting in a biological effect.

38
Q

Describe paracrine action.

A

Stimulus acts on a cell. Cell produces cytokine which then binds to a receptor on the surface of a nearby cell, resulting in a biological effect.

39
Q

Describe endocrine action.

A

Stimulus acts on a cell. Cell produces cytokine which then moves via the circulation to a distant cell, where it binds to a cell surface receptor, resulting in a biological effect.

40
Q

How are inactivated complement components produced by the liver activated?

A

Part of the protein is cleaved, producing the activated enzyme which can trigger an enzyme cascade.

41
Q

What are lectins?

A

Proteins which bind to carbohydrates.

42
Q

Give 2 lectins which bind to carbohydrates only found on bacteria (and thus trigger the complement pathway)

A

CRP (C Reactive Protein)

MBL (Mannan Binding Lectin)

43
Q

What is the alternative pathway of complement activation?

A

Bacterial surfaces directly activate complement.

44
Q

What do the proteins cleaved from inactive complement components do?

A

They are inflammatory cytokines, e.g. C3a, C5a.

45
Q

What does the final common pathway in the complement system produce?

A

A membrane attack complex: MAC. It inserts itself in pathogens’ membranes, leading to lysis.

46
Q

Name 3 control mechanisms of the complement system.

A

Short half-life, diluted in biological fluids, specific regulatory proteins (both circulating and membrane bound).

47
Q

What are three roles of antibodies?

A 
Complement activation (immune complex)
Opsonisation
Cell Activation (Fc receptors)
Neutralisation
Agglutination
48
Q

Which regions are most responsible for antibody variation?

A

There are 3 regions in the variable region which are hypervariable, called complementarity determining regions (CDRs).

49
Q

Define antibody affinity.

A

The strength of the total non-covalent interactions between a single antigen binding site and a single epitope on the antigen.

50
Q

Define antibody avidity.

A

Overall strength of multiple interactions between an antibody with multiple binding sites and a complex antigen with multiple epitopes. (This is a better measure of binding capacity in biological systems).

51
Q

Define antibody cross-reactivity.

A

When elicited in response to one antigen can sometimes recognised different, similar antibodies.

52
Q

Detail IgG.

A

Most abundant immunoglobulin. Monomer. Actively transported across the placenta for natural passive immunity. Major activator of classical complement pathway.

53
Q

Detail IgA.

A

Second most abundant immunoglobulin. Monomer in blood, dimer in secretions (with a J-chain linking the 2 monomers). Protects mucosal surfaces from pathogens.

54
Q

Detail IgM.

A

Pentameric molecule (5 monomers). Mainly confined to blood. First Ig synthesised after exposure to antigen -PRIMARY RESPONSE. Efficient at agglutination.

55
Q

Detail IgD.

A

Very low serum concentrations. Surface IgD expressed early in B cell development. Involved in B cell development and activation.

56
Q

Detail IgE.

A

Extremely low levels. Responds to parasites and allergens. Binds to high affinity Fc receptors on mast cells & basophils. Triggers mass cell activation (degranulation –> histamine release).

57
Q

What does the B-cell receptor (BCR) consist of?

A

An immunoglobulin and a heterodimer (IgA and IgB (alpha and beta) THESE ARE NOT ANTIBODIES. The heterodimer is also known as CD79) which are bound together by disulphide bridges, span the membrane and have cytoplasmic tails.

58
Q

How is a massive repertoire of BCRs produced from only a few genes?

A

Each BCR receptor chain is encoded by separate multigene families on different chromosomes. During B cell maturation, these gene segments are rearranged and brought together: immunoglobulin gene rearrangement.

59
Q

What is required to activate a naïve B-cell?

A

Antigen + either an accessory signal (such as direct microbial constituents) or T-helper cell.

60
Q

What is thymus dependent activation?

A

Antigen + T-helper cell used to activate naïve B-cell. This happens for all Ig classes and produces MEMORY.

61
Q

What is thymus independent activation?

A

Antigen + microbial constituents activate naïve B-cell. This happens for IgM and doesn’t produce memory.

62
Q

Describe the structure of the T-cell receptor (TCR)

A

Similar to the Fab region of an antibody. Consists of an alpha and beta chain (each with a variable and constant region) linked by disulphide bonds. Both chains span the membrane and have cytoplasmic tails.

63
Q

What are the 2 major populations of T lymphocytes?

A

Those which use the CD4+ receptor (class II restricted). Those which use the CD8+ receptor (class I restricted).

64
Q

Describe the maturation of T-cells in the thymus.

A

Immature T-cells (double negative) arrive at outer cortex of the thymus from the bone marrow. They then become preTCR+ (Beta + surrogate alpha TCR). They then become double positive. Finally, in the medulla, they undergo selection process to see which type of MHC they recognise, and become either CD8+TCR+ or CD4+TCR+.

65
Q

How are thymocytes selected in the thymus?

A

Useless (can’t recognise MHC) die by apoptosis.
Useful (recognise MHC weakly) receive signal to survive (positive selection). Dangerous (recognise MHC strongly) die by apoptosis (negative selection).

66
Q

Describe the structure of MHC class II.

A

Two equal sized chains (a1 and a2 on a chain and b1 and b2 on b chain). Each chain has a transmembrane region so an MHC II has 2 transmembrane regions. A CD4+ binds to b2.

67
Q

Describe the structure of MHC class I.

A

A heavy chain (a1,a2,a3) with a transmembrane region and a light chain (b2 microglobulin) which is non-covalently bonded to the heavy chain. CD8 binds to a3.

68
Q

Which class of MHC presents endogenous antigens (generated from normal metabolism or because of viral or intracellular bacterial infection)?

A

MHC Class I - to CD8+ cells.

69
Q

Which class of MHC presents exogenous antigens?

A

MHC class II - to CD4+ cells.

70
Q

What does an invariant chain do?

A

It directs MHC class II molecules from the ER where they are synthesised to a vesicle containing the exogenous antigen.

71
Q

What does the Autoimmune REgulator (AIRE) do?

A

It is a transcription factor which allows thymic expression of genes expressed in peripheral tissues to promote self-tolerance.

72
Q

Why are pregnant women naturally immunosuppressed?

A

A pregnancy is basically a parasitic infection as the new antigen is expressed as foreign on MHC I.

73
Q

What is the difference between CD4 Th1 and CD4 Th2 cells?

A

CD4 Th1 cells activate macrophages: CD4 Th2 cells assist in B cell proliferation.

74
Q

What is margination?

A

Process in which free-flowing leukocytes exit the central blood stream.

75
Q

What are Peyer’s Patches?

A

Peyer’s patches are small masses of lymphatic tissue found throughout the ileum region of the small intestine. They monitor intestinal bacteria populations and prevent the growth of pathogenic bacteria in the intestines.
Form part of GALTs (gut associated lymphoid tissue)

76
Q

What is diapedesis?

A

Migration of cells through blood capillary walls into the tissues.

77
Q

What is a histiocyte?

A

A stationary phagocytic cell present in connective tissue.

78
Q

What is the role of the dendritic cells?

A

Recognise pathogens and act as antigen presenting cells and travel to the nearest lymph node.

79
Q

What are the 3 fates of a mature B cell?

A

Plasma cell
Memory cell
Somatic hypermutation and affinity maturation.

80
Q

Give the four classes of innate immune system defensive barriers.

A

Anatomical
Physiological
Phagocytic
Inflammatory

81
Q

What is antibody-dependent cell-mediated cytotoxicity?

A

Natural Killer cells express receptors which bind to antibody coated cells.

Molecules, Cells and Diseases (MCD) and Epidemiology in Practice (EiP) (9 decks)

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