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Microbiology > Immunity > Flashcards

Immunity Flashcards

1
Q

Define pathogen.

A

An organism with the potential to cause disease.

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2
Q

Define immunity, immune system and immune response.

A
  • the ability to resist disease
  • a network of cells, tissues and organs that functions to defend the body against pathogens
  • coordinated reaction of immune system
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3
Q

Define antigen.

A
  • Molecules that are recognised by the immune system and can stimulate an immune response.
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4
Q

What precursor cell gives rise to most cells involved in innate response?

A

common myeloid progenitor

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5
Q

What does common lymphoid progenitor give rise to?

A
  • B and T lymphocytes and NK cells
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6
Q

Which immune cell triggers main characteristics of inflammation?

A
  • Macrophages produce cytokines triggering heat and swelling.
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7
Q

What does the innate immunity involve? (4)

A
  • Rapid response
  • Recognises pathogen-associated molecules
  • Facilitates the adaptive response (calls for reinforcements)
  • Components include: physical barriers (skin, mucus, chemical barriers), proteins (complement, cytokines, chemokines), cells (macrophages, granulocytes)
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8
Q

Describe the 2 forms of adaptive immunity.

A
  • Humoral (liquid/soluble part of body): mediated by antibodies derived from B cells.
  • Cellular: mediated by T cells.
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9
Q

Define epitope.

A
  • Only part on antigen that is recognised by lymphocytes.
  • A single antigen may have multiple epitopes.
  • Each lymphocyte is specific for one epitope
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10
Q

Function of B cells.

A
  • Primary defence against extracellular pathogens.
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11
Q

Function of T cells.

A
  • Primary defence against intracellular pathogens.
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12
Q

What are the primary lymphoid organs and their function?

A
  • Bone marrow (B cells) and thymus (T cells).

- Development and maturation of lumphocytes.

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13
Q

What are the secondary lymphoid organs and their function?

A
  • Spleen, lymph nodes, tonsils, Peyer’s patches, mucosa-associated lymphoid tissue (MALT), appendix
  • Where lymphocytes encounter pathogens and become activated.
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14
Q

Where are most lymphocytes found?

A
  • More than 50% are found in lymph nodes and spleen.
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15
Q

Function of the spleen.

A
  • Acts primarily to filter blood and fight infection.

- Largest lymphatic organ

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16
Q

Describe the coordinated response of the immune system.

A
  • Lymphocytes recirculate through lymph node/spleen via blood.
  • Antigens/pathogens are funnelled from the periphery into the local lymph nodes.
  • Lymphocytes encounter antigen in the secondary lymphoid organs.
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17
Q

How does lysozyme act as a chemical barrier?

A
  • Exposes the lipid bilayer.
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18
Q

How does the immune system detect pathogen?

A
  • Components of innate immunity recognise pathogen-associated molecular patterns (PAMPs) and microbe-associated molecular patterns (MAMPs).
  • PAMPs is detected by pattern recognition receptors (PRRs- on cell can express many PRRs).
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19
Q

What are macrophages and their function in immunity? (3)

A
  • Reside in blood (monocyte precursor) and tissues (macrophage)
  • Usually the first to encounter pathogen
  • Function include phagocytosis, antigen presentation and cytokine production.
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20
Q

Name a few PRRs and describe one. (2)

A
  • Mannose receptor, scavenger receptor, C-type receptor and toll-like recpetors (TLRs)
  • TLR-4 recognises lipopolysaccharide (LPS). TLR5 recognises flagellin, TLR 3, 7, 8, 9 recognises internal stranger signals.
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21
Q

Function of NF-kB.

A
  • A protein that controls transcription of DNA, cytokin and or/chemokine production and invovled in inflammatory response.
22
Q

How does opsonisation enhance phagocytosis? (3)

A
  • Host proteins called opsonins coats the bacteria presenting more markers for phagocytic cell to be able to see/bind to the pathogen and engulf it.
  • Opsonins are soluble proteins which bind to pathogens. eg. antibodies (IgG), C3b (complement protein)
  • Phagocytic cells express receptors that recognise these molecular tags. eg. FcR (binds antibody) or CR1
23
Q

Function of cytokine and chemokine.

A
  • Important in producing inflammation, changing permeability of blood vessels and recruiting cells to site of infection.
  • Cytokines block viral spread (interferons block transcription/translation), activate other cells (NK cells, macrophage), upregulate MHC molecules
  • Chemokines regulate movement of cells and mobilise/recruit immune cells.
24
Q

What are granulocytes and list some examples?

A
  • Characterised by secretory granules in their cytoplasm and multi-lobed nucleus. eg. neutrophils, eosinophils, basophils
25
Q

Function of neutrophil. (5)

A
  • Most common white blood cell and is largely stored in bone marrow.
  • Mobilised by following concentration gradients of chemotaxins/chemokines (interleukin 8).
  • Predominant role is phagocytosis (express PRRs and receptors for complement and antibody (FcR))
  • Short lived (die after destroying pathogen- pus)
  • Expels sticky strands of DNA (NETs) to capture and kil pathogen.
26
Q

Function of eosinophils. (4)

A
  • Mainly found in tissues
  • Role in anti-parasite immunity (protozoans and helminth worms)
  • Contribute to allergic responses
  • Triggered to release content of their granules into surrounding area. eg. cytotoxic compounds.
27
Q

Function of basophils. (2)

A
  • Similar role to eosinophils and mast cells

- Important for allergic response (release of histamine, causes inflammtion).

28
Q

Function of mast cells. (2)

A
  • Only found in tissues
  • Its cytoplasm is full of granules containing histamine and active agents which are important for recruiting other cells to site of infection, increasing inflammation and triggering muscular contractions.
29
Q

Function of dendritic cells.

A
  • Programmed to detect and phagocytose pathogens.
  • Display foreign antigen on surface to present to lymphocytes.
  • Involved in T cell activation.
30
Q

Difference between immature and mature dendritic cells.

A
  • Immature/resting DC: sample environment for antigen, phagocytic, pattern recognition receptors.
  • Mature DC: morphological changes, migrate to lymph node, present antigen to T cells.
31
Q

Function of NK cells. (4)

A
  • Secrete anti-viral cytokines. eg. interferon-gamma and tumour necrosis factor-alpha.
  • Respond to changes in expression of self proteins.
  • Activated NK cell release perforin and granzymes that together trigger the target cell to commit suicide.
  • May also recognise and kill cells opsonised by antibodies (ADCC).
32
Q

Function of complement. (4)

A
  • Soluble proteins in blood that can interact with pathogens to mark them for killing.
  • Activated sequentially in a cascade, which can be activated by 3 different pathways.
  • All pathways converge at the activation of C3 protein to C3a (recruits phagocytes/inflammatory cells) and C3b (tags bacterium for destruction/phagocytosis).
  • The 3 pathways are classical, lectin and alternative.
33
Q

What can antibodies do?

A
  • Opsonise bacteria, neutralise viruses, sensitise mast cells and activate complement.
34
Q

What does a naive cell mean?

A
  • Haven’t encountered a foreign antigen yet.
35
Q

What is the difference between negative and positive selection of B cells?

A
  • Negative mean alteration, elimination or inactivation of B-cell receptors that bind to components of the host body.
  • Positive mean promotion of a fraction of immature B cells to become mature B cells in the secondary lymphoid tissues.
36
Q

What is conformational epitope and linear epitope?

A
  • Multiple different amino acids coming together in the shape of their 3-D structure (no continuous).
  • Continuous amino acids in a linear fashion can be recognised.
  • Denaturation results in the loss of conformational epitopes.
37
Q

Difference between surface Ig and secreted Ig.

A
  • Secreted Ig has hydrophobic tail removed so it doesn’t embed into cell surface.
38
Q

What is Fc and what is Fab?

A
  • Stalk of Y is the crystallisable fragment and is composed of only the constant region.
  • Top of Y is two antigen-binding fragments composed of both a constant and a variable region.
39
Q

What are the 5 classes/isotopes of immunoglobulin and what region of the antibody do they reside in? (3)

A
  • IgM, IgD, IgG, IgA, IgE
  • Determined by the heavy chain constant region gene segments.
  • Effector function of antibody is largely derived from the Fc region.
40
Q

Describe IgM. (4)

A
  • Expressed as receptor on naive B cells and early during infection.
  • Secreted as pentamer
  • Linked by J chains
  • Efficient at activating complement
41
Q

Describe IgG. (4)

A
  • Major immunoglobulin class in serum and secondary response.
  • Binds receptors (FcRs) expressed by monocytes, macrophages and NK cells.
  • Can activate complement
  • Can cross placenta
42
Q

Describe IgA. (3)

A
  • Expressed on the cell surface as a monomer
  • Secreted as dimer (held together by J chain that binds to the secretory component)
  • Prominent in mucosal secretions (airways, gut, breast milk)
43
Q

Describe IgD. (2)

A
  • Expressed on naive B cells (along with IgM)

- Not really seen in secreted form

44
Q

Describe IgE. (2)

A
  • Important in responses to parasites.

- Can cause allergic reactions.

45
Q

Where does thymic education occur and what selections are involved? (3)

A
  • Occurs in thymus where TCR is first expressed.
  • Positive selection: If TCR has no capacity to bind slef MHC molecules, the T cell will die.
  • Negative selection: If TCR binds to host MHC/peptide complexes present in thymus too tightly, T cell will die.
46
Q

Describe the structure of a TCR. (4)

A
  • Heterodimer of the alpha and beta chain
  • Membrane bound
  • Multiple V gene segments
  • One constant-alpha gene segment and one constant-beta gene segment
47
Q

Function of T cell receptors.

A
  • Can only bind short linear epitopes.
48
Q

Which cells express MHC class 2?

A
  • macrophages, B-cells and dendritic cells
49
Q

What proteins are presented on MHC 1 and MHC 2?

A
  • Present peptides from endogenous proteins.

- Present peptides from exogenous proteins.

50
Q

How is peptide presented onto MHC class 1? (2)

A
  • Peptides are created by proteolysis in the cytoplasm by proteasome.
  • Peptide transported through TAP and loaded into MHC class 1 in the lumen of the ER.
51
Q

What are the 3 signals required to activate naive T cell?

A
  • Presentation of MHC and antigen to TCR.
  • Costimulation through CD28:B7 (CD80/86) for T cell expansion.
  • Cytokine receptor signalling for T cell differentiation.
52
Q

How is dendritic cell activated and what results from it?

A
  • Binding of pathogens, signalling by PRR (on DC) following ligation with molecular patterns (PAMPs) on pathogens.
  • Increased surface expression of MHC 1 & 2, expression of co-stimulatory molecules (CD80, CD86), secretion of cytokines, Mature DCs lose capacity to capture antigen.

Microbiology (8 decks)

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