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Semester 3 - Infection > Session 6 - Adaptive immune system > Flashcards

Session 6 - Adaptive immune system Flashcards

1
Q

What are the three main features of an antigen presenting cell?

A

• Strategic location of B and T cell interaction
• Pathogen capture
Diversity in pathogen sensors

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2
Q

Where are antigen presenting cells found?

A
  • Skin
    • Mucous membrane
    • Lymphoid organs
    • Blood circulation
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3
Q

Why is diversity in pathogen sensors required?

A
  • To detect extracellular pathogens (bacteria)

* To detect intracellular pathogens (viruses)

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4
Q

Give four antigen presenting cells

A
  • Interdigitating dendritic cells
    • Langerhans’ cells
    • Macrophages

B cells

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5
Q

Where are interdigitating dendritic cells found, and to what do they present?

A

• Lymph nodes

T cell and B cells

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6
Q

Where are langerhans cells found, and to what do they present?

A
  • Skin

* T cells

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7
Q

Where are macrophages found, and to what do they present?

A
  • A whole range of tissues

* B and T cells

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8
Q

Where are B cells found and to what do they present?

A
  • Lymphoid tissues

* T cells

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9
Q

What is HLA? (human leukocyte antigen)

A
  • Also known as MHC, protein holders expressed on cell surface which hold and “present” specific bacterial or viral peptides to T cells
    • HLA class 1 - Binds intracellular microbes, recognised by (CD8) cytotoxic T cells
    • HLA class 2 - Binds extracellular microbes, recognised by (CD4) T helper cells
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10
Q

Give three types of antigen presenting cells which express HLA’s

A
  • B cells
    • Dendritic cells
    • Macrophages
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11
Q

How are extracellular microbes (bacteria) dealt with by antigen presenting cells?

A
  • Bacteria phagocytosed
    • Broken down in phagosome
    • Processed and placed on HLA class 2
    • Presented to CD4 T cells
    • Provides humoral immunity
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12
Q

How are intracellular microbes (viruses) processed?

A
  • Proteosomes (activated by interleukins) find and destroy virus, collect peptide
    • Peptide presented on HLA class 1 to cytotoxic CD8 T cellls
    • Cell dependent immunity
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13
Q

What are two types adaptive immunity?

A

• Humoral

Cell mediated

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14
Q

What is humoral immunity?

A

• Aspect of immunity mediated by macromolecules found in extracellular fluids, such as antibodies and complement

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15
Q

What is cell mediated immunity?

A

• Involved phagocytes, cytotoxic T-lymphocytes and cytokines instead of antibodies

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16
Q

What types of HLA’s is found on all cells?

A
  • HLA-1

* Expression of internal peptides. All cells contain peptides, so all cells have HLA-1.

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17
Q

What are the two different types of T cell?

A
  • Cytotoxic CD8 T cells, which kill cells (cell dependent immunity)
    • B cell activating CD4 T helper cells (humoral immunity)
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18
Q

How are T cell receptors diversified to be able to recognise any antigen put to them?

A

• Not enough space on genome for individual genes

Genetic recombination produces diversity of receptors required

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19
Q

What is a danger of T cell recombination?

A

• Malignancy

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20
Q

How does binding of a HLA molecules to a T cell receptor cause activation of the T cells effects?

A

• Once enough HLA molecules bound, T cell activates kinases which trigger transcription factors within the cell

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21
Q

Why is it important for the population to have a variety of different types (polymorphic) of HLA for each class?

A
  • Type of HLA determines what antigen (peptide) can be expressed
    • Diversity in HLA means that there will always be a member of the population who can express a particular microbial antigen and thus mount an immune response
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22
Q

How are HLA genes expressed?

A
  • Co-dominant

* Both parental genes are expressed, increasing number of potential HLA molecules

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23
Q

How many different genes are there for class 1 HLA?

A

3

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24
Q

How many different genes are there for class 2 HLA?

A

6/8

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25
Q

Outline the features of a HLA?

A
  • Peptide binding cleft - variable region with highly polymorphic residues
    • Broad specificity
    • Causes response in T cells (Class 1 - CD8 T cells, Class 2 - CD4 T cells)
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26
Q

What are bacterial peptides presented by and presented to?

A
  • HLA class 2 peptides
    • Presented to CD4+ T cells
    • Humoral immunity
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27
Q

What are viral peptides presented by and presented to?

A
  • HLA class 1 presenting viral peptides
    • To CD8 T cells (cytotoxic)
    • Cell dependent immunity
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28
Q

What is a slow progressor in terms of a patient response to HIV?

A
  • Right HLA presented to CD4 cells due intrinsic HLA polymorphism
    • T cell response generated as antigen presented
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29
Q

What is a rapid progressor?

A
  • Homozygote HLA-1 marker, less HLA polymorphism

* Weak T cell response due to lack of presentation of antigen

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30
Q

Give three clinical problems concerning HLA molecules

A
  • Organ transplant rejection
    • Autoimmune disease
    • Cross reactivity between microbial and host antigens
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31
Q

What is a major cause for organ transplant rejection?

A
  • HLA molecules mismatch between donor and recipient (allograft)
    • T cells present in donor tissue attack recipient’s tissue with different HLA markers
    • Graft versus Host reaction
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32
Q

Give two conditions in which there is a HLA association and autoimmune disease

A

• Ankylosing spondylitis - HLA B27 found in 90% of patients

Insulin dependent Diabetes mellitus - HLA DQ2 found in 50-75% patients

33
Q

What is cross reactivity?

A

Antibodies can sometimes combine with more than one antigen, if the antigens are similar. This can cause an immune response against host cells if things go awry.

34
Q

Give three conditions which come about as a result of cross reactivity between microbial and host antigens

A
  • Rheumatic heart disease
    • Guillian-barre syndrome
    • Type 1 diabetes
35
Q

What is the cross reactivity in rheumatic heart disease?

A

• Streptococcus pyogenes

Antigen in cardiac muscle

36
Q

What is the cross reactivity in diabetes type 1?

A
  • Coxsakieviruses

* Pancreatic islet cells

37
Q

Where are T cells matured?

A

• Thymus

38
Q

What do T cells produced to aid in defence against infection long term?

A

• Memory cells

39
Q

What do CD8+ T cells do

A

• Protect against intracellular pathogens

40
Q

What do CD4+ T cells do?

A

• Provide help for antibody production and regulate immune response

41
Q

Outline the structure of a T cell receptor

A

• Possess A and B chain, each with variable sections

42
Q

What factors are required for a T cell to become activated?

A
  • Must bind to HLA molecules

* Must bind to specific antigen

43
Q

What happens after T Cells are exposed to appropriate stimulatory factors?

A

They begin to mature

44
Q

What are the three types of helper cells a naive CD4+ T cells can mature into?

A

• T helper cells (Th1/Th2)

Memory cells

45
Q

What is a naive T helper cell?

A

• One which has never encountered an antigen

46
Q

What is the difference between a TH1 and a TH2 helper cell?

A
  • A TH1 helper cell activates cytotoxic t cells and is involved in cell mediated immunity
    • A TH2 helper cell is required for priming B cells to produce antibodies - Inolved in humoral immune system
47
Q

What are the two main types of cells a CD8+ cell can differentiate into?

A
  • Cytotoxic T cells

* Memory cells

48
Q

What are the three main functions of CD4+ TH1 (TH1!!!) cells?

A 
• Killing of infected cells 
		○ Cytotoxic T cells
		○ Natural killer cells
	• Phagocytosis
		○ Macrophages
	• Antibody production (B cells)s

IgG

49
Q

What are the four functions of CD4+ TH2 cells (TH2 SILLY)

A 
• Killing of parasites
		○ Eosinophils
	• Antibody production 
		○ B cells
	• Mast cell activation
		○ IgE
	• Mucosal protection

IgA

50
Q

How do cytotoxic T cells (CD8+ T cells) kill virus infected cells?

A
  • Detect HLA 1 with the viral content
    • Perforins granzymes released
    • Destroys viral cells
51
Q

What T cells fight bacteria?

A

• CD4+ TH2 cells

○ Humoral immunity

52
Q

What T cells fight viruses?

A

• CD4+ TH1 cells
• CD8+ T cells
○ Cell dependent immunity

53
Q

Where are B cells formed?

A

• Bone marrow

54
Q

What is the antigen receptor for B cells?

A

• B cell receptor

55
Q

Do B cells make memory cells?

A

• Yes

56
Q

What are the two main functions of B cells

A
  • Protection against extracellular pathogens
    • Antigen presentation to T cells
    • Produce many different types of antibody
57
Q

What is the main difference between B cells and T cells?

A

• B cells can be activated by proteins, lipids, nucleic acids, along with T cell binding to HLA 2

T cells can only be activated by small peptides

58
Q

How do B cells mature?

A

Plasma cells produced via replication

59
Q

How are B cells primed?

A
  • Recognises antigen on infected tissue

* TH2 helper cells

60
Q

What is the fate of activated B cells?

A
  • Become plasma cells or

* Memory B cells

61
Q

Give four characteristics on humoral response

A
  • Faster
    • Stronger
    • Longer duration
    • Higher affinity iostype switch
62
Q

Name four important types of antibodies in the order they are produced

A
  • IgM
    • IgG
    • IgA

IgE

63
Q

What does IgM do?

A
  • First antibody produced during an immune response
    • Neutralises toxins
    • Activates complement via classical pathway
64
Q

What does IgG do?

A
  • Main antibody secreted into blood after class switching
    • Opsonise bacteria for phagocytosis
    • IgG pumped across placenta in large quantities and present in mothers breast milk, giving babies extra passive immunity
65
Q

What does IgA do?

A
  • Produced late in immune response
    • Found on mucosal surfaces
    • Forms a secretory dimer which protects it from enzymes, important in gut mucosa
66
Q

What does IgE do?

A
  • Binds to mast cells even when antigen absent
    • Causes mast cell degranulation, releasing granules, histamin and cytokines (allergic response)
    • Used against parasitic worms
67
Q

What is the difference between passive and active immunity?

A
  • Passive - Transfer of active antibodies from individual to another. Maternal transfer to foetus is a key example.
    • Active - Host is exposed to antigen and generates own immunological response and antibody production.
68
Q

What are vaccines intended to do?

A

• Aim to produce memory B and Th2 cells, which produce large amounts of antibody on exposure to antigen.

69
Q

Give three vaccines given at two months?

A
  • Tetanus
    • Haemophilus
    • Menigococcus C
70
Q

Give a vaccine given at 1 year

A

• MMR

71
Q

Give a vaccine given at 10-14 years

A

• BCG

72
Q

Give a vaccine given in elderly and high risk patients

A

• Influenza

73
Q

Give three types of vaccines

A
  • Live attenuated vaccines
    • Dead vaccines
    • Subunit vaccines
74
Q

What is an attenuated live vaccine?

A

• Contains pathogens that have been weakened to the point they will not cause disease

75
Q

Give an advantage and a disadvantage of liver attenuated vaccines

A
  • +’ve - Live inside cells and present on HLA class 1 molecules
    • -‘ve - Can spontaneously revert to wild type, and can cause disease in immunodeficient patients
76
Q

What is a dead vaccine?

A

• Dead micro-organism given. Antigens stimulate immune response

77
Q

Give an advantage and disadvantage of dead vaccines

A
  • +’ve - No chance of reverting to wild type
    • -‘ve - Less potent that live attenuated vaccines as cannot get inside cell

-‘ve - New vaccines sometimes have to synthesised every year, due to drift and shift

78
Q

What is a subunit vaccine?

A

• Vaccines derived from cell components or excretory products

79
Q

Give an advantage and disadvantage of subunit vaccines

A
  • +’ve - Do not replicate and rarely cause side effects
    • -‘ve - Require adjuvants

-‘ve - may not prevent infection, just common complications

Semester 3 - Infection (14 decks)

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