Adaptive immune system I Flashcards

1
Q

What are the 2 types of adaptive immune response?

A
  • Cell mediated
  • Humoral
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2
Q

Briefly describe the innate response to new infection and why it’s important

A
  • Response to new infection fast
  • Acts on pre-determined non-self signals
  • Sometimes can be primed/trained for intense reactivation (innate memory)
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3
Q

What are the components of the cell mediated innate response?

A
  • Phagocytes
  • Natural killer cells (NK cells)
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4
Q

What are the components of the humoral response?

A
  • Complement and pentraxins (CRP)
  • Pattern receptors (soluble TLR- toll-like receptors, makes response quick)
  • Enzymes (lysozyme)
  • Cytokines releasing antimicrobials
  • Binding proteins (Lactoferrin)
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5
Q

Briefly describe the adaptive response to new infections

A
  • Slow
  • Selects for specific signals and generates memory
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6
Q

Where are T and B cells made?

A
  • Bone marrow with a randomly assigned antigen-binding specificity
  • T and B cells can have the same specificity
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7
Q

What cells and molecules are involved in the innate immune response?

A
  • Dendritic cell
  • Mast cell
  • Macrophage
  • NK cell
  • Complement protein (mark pathogens to be destroyed)
  • Neutrophil - granulocyte
  • Eosinophil - granulocyte
  • Basophil - granulocyte
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8
Q

What cells and molecules are involved in the adaptive response?

A
  • B cell
  • Antibodies
  • CD4+ T cell (T helper cell)
  • CD8+ T cell (T cytotoxic cell)
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9
Q

Where are T lymphocytes developed?

What happens to them there?

A

Migrate to Thymus gland, become CD8+, CD4+ or are destroyed if strongly recognise self antigens (central tolerance)

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10
Q

Where are B lymphocytes developed?

A
  • Bone marrow
  • Developed and matured in bone marrow to express a single epitope antibody used as a receptor to bind to an antigen
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11
Q

What is T cell priming?

A

The activation and clonal expansion of a naive T cell on initial encounter with antigen on the surface of an antigen-presenting cell

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12
Q

Describe the endogenous pathway of T cell priming

A
  • Endogenous antigen pathway leads to cytotoxic (CD8) T cell priming
  • Antigen binds to APCs
  • These cells are infected by the virus
  • Viral proteins in the cytoplasm are detected and processed
  • Viral antigens presented with MHC class I molecule on cell surface
  • CD8+ cell recognises antigen, becomes cytotoxic, begins to make cytokines
  • Cytotoxic T cell (CTL) proliferates making memory cells, and CTL cells looking for cells with presented antigen
  • Infected cell destroyed by cytotoxic cell
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13
Q

Describe the exogenous pathway of T cell priming

A
  • Exogenous pathway leads to T helper cell priming
  • Antigen (pathogen) engulfed by dendritic cell or macrophage via phagocytosis
  • Antigen processed into small peptides
  • Antigen presented with MHC class II molecule on cell surface
  • CD4 T helper cell recognises presented antigen
  • CD4 Th cell becomes primed and can help with either B cell activation or macrophage activation
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14
Q

Describe antibody-antigen interaction

A
  • Non covalent interactions
  • Electrostatic, hydrophobic, van der Waals, Hydrogen bonds
  • Depends on antibody binding site being exactly complementary sterically and chemically, with a site on the surface of the antigen
  • A single antigen can have many possible binding sites (epitopes)
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15
Q

Describe the structure of antibodies

A
  • Immunoglobulin + glycoprotein
  • 2 identical antigen binding sites
  • A hinge ‘H” region - flexible space between binding sites
  • Protease cleavage generates large fragments called Fab (variable region, antigen binding) and Fc (constant region, crystallisable)
  • 4 polypeptide chains held together by non-covalent interactions by disulphide crosslinks between cysteine
  • 2 identical Heavy chains
  • 2 light chains
  • Carbohydrates help assembly and binding to cells
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16
Q

What is the function of constant regions?

A
  • Fc constant region allows binding of phagocytes to receptors of the antibody, activates complement
17
Q

What is complement?

A

System of plasma proteins activated directly by pathogens or indirectly by pathogen-bound antibody

They interact with pathogens and mark them so that phagocytes are able to detect and destroy them

18
Q

What is the function of the variable region?

A
  • Fab variable region allows for antigen binding, contributes to antigen-binding site
19
Q

Describe the B cell activation pathway that is independent of T cells

A
  • B cell receptors bind to antigen on pathogens
  • Activation initiates proliferation with some cells being memory cells and other cells being committed to antibody production
  • Activated B cells convert to plasma cells and begin making antibody
  • This pathway is restricted to specific antigens (will always make only 1 type of antibody)
  • Can lead to problems such as toxic shock syndrome (too much antibody)
20
Q

Describe the B cell activation pathway that is dependent on T cells

A
  • B and Th cell interact, this activates the B cell
  • Activation initiates B cell proliferation with some cells being memory cells, others being committed to antibody production
  • Antibody production required co-stimulation with a Th cell that was already screened against self, hence avoided autoimmune response
21
Q

Define epitope

A
  • A single antigen that has multiple binding sites
22
Q

Why is the immune system classed as polyclonal?

A
  • More than 1 clone of B cells is generated
  • More than one immunoglobulin is synthesised
    This is because:
  • Multiple antigens on organism
  • Multiple epitopes on each antigen
  • More than one immunoglobulin may recognise the same epitope
23
Q

How do antibodies fight infection?

A
  • By coating and neutralising a pathogen- if a virus is coated with antibody, it can’t bind to its receptors on the cell surface
  • By activating complement - which can then form holes in a bacterial cell membrane
  • By opsonisation - phagocytes have Fc receptors on their cell membrane, bind to pathogens coated with antibody and phagocytose them
24
Q

Describe the 2 structures of the IgM antibody

A

Structure 1: Membrane bound
- Monomer of basic subunit B cell receptor
- Extra heavy chain domain that is membrane bound in the B cell

Structure 2: Secreted
- Pentamer of basic sub=unit in plasma (secreted + highly antigenic - many antigens)
- Contains a J chain - a polypeptide involved in pentamer polymerisation

25
Q

What is the order of Ig production?

A

IgM - first antibody class made
IgG - second antibody class made

26
Q

What is the function of IgG?

A
  • Major class overall (75% of Ig)
  • Major class made by secondary responses
  • Only antibody class able to cross placenta and protect the developing foetus
  • Good at activating complement via classical pathway (removing the pathogen)
  • Acts as opsonin inducing phagocytosis - Fc region recognised by ‘Fc receptors’ on surface of immune cells, e.g. neutrophils and macrophages
  • Can be present for long periods in serum, so may indicate past exposure, not current infection
27
Q

What is the function of IgM?

A
  • Presence indicates a recent primary response to that antigen
  • Implies a current primary infection
  • Activates complement via classical pathway (due to pentameric structure)
  • Higher valency of pentameter increases overall affinity (by binding higher number of epitopes)
  • Binds to immune cells via Fc receptor (ie, inducing phagocytosis)
28
Q

What is the primary response?

A
  • Body’s first response to unfamiliar infection
  • Slow, specific response
  • Produces lasting memory cells
29
Q

What is the process of isotope switching?

A
  • Biological mechanism that changes a B cell’s production of an immunoglobulin from one type to another
30
Q

What is the secondary response?

A

When a pathogen that has already infected the body before reinfects the body

Much faster and stronger response due to memory cells

31
Q

What is the function of IgA?
Which one is serum IgA and which is secretory IgA?

A
  • 2 forms IgA1, IgA2 (differ in constant regions)
  • IgA1 is predominant in serum
  • IgA2 is predominant in secretions
  • Monomer - This is Serum IgA
  • Most abundant class in external secretions (milk, sweat, tears, saliva, gut fluids etc)
  • Serves as opsonin (eosinophils, neutrophils, some macrophages)
  • Main immunoglobulin in mucosal sites; sometimes occurs as dimer - This is secretory IgA
    First line protection at external surfaces:
  • Initiates localised mucosal response different from more general circulating immune response
  • Neutralises pathogens, prevents binding to cell surface receptors
  • Secretory components protects IgA from degradation, hence it can work in harsh environments (eg. GI tract)
32
Q

What is the function of the IgE antibodies?
Are they normally in high or low concentration?

A

Harmful function in allergies:
- Binds to specific Fc receptor on mast cells and basophils releasing histamine

Useful function is response to parasitic worms
- Release chemicals from mast cells
- Activates eosinophils (via Fc receptor binding)

Normally low concentration in circulation
- Raised in allergic patients
- Raised in infections with large parasites
- Over response can cause anaphylactic shock