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YEAR 1 - Biochemistry and Medical Genetics (Anton) > 44. Blood > Flashcards

44. Blood Flashcards

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1
Q

What is an antigen?

A

Any structure which elicits an adaptive immune response.

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2
Q

How are antigens recognised in the adaptive immune response?

A
  • By specific antigen receptors which bind to structures (antigens) on or produced by pathogens.
  • The antigen receptors can be either secreted or cell-associated.
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3
Q

What is the main cell type responsible for detecting antigens?

A

Lymphocytes (both B and T)

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4
Q

Where do lymphocytes most commonly encounter antigens?

A

Secondary lymphoid organs:

  • Lymph nodes
  • Spleen
  • Peyer’s patches
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5
Q

What are the antigen receptors on B and T lymphocytes called?

A
  • B-cell receptor (BCR ) immunoglobulin (Ig)
  • T-cell receptors (TCRs)
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6
Q

What are immunoglobulins?

A

It is just another word for antibodies.

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7
Q

What are the two forms of immunoglobulin (antibodies)?

A
  • Cell-associated
  • Secreted
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8
Q

Compare the functions of the cell-associated and secreted forms of immunoglobulins (antibodies).

A
  • Cell associated -> Signalling receptor for detecting antigens
  • Secreted -> Elimination of foreign molecules
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9
Q

What lymphocytes are immunoglobulins found on?

A

B lymphocytes

(T lymphocytes also have similar molecules though, called T-cell receptors)

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10
Q

Are B-lymphocyte immunoglobulins and TCRs (T-cell receptors) just found on cells or are they also found as secreted individual structures?

A
  • Immunoglobulins are found on both B-lymphocytes and as secreted structures
  • TCRs are found only on T-lymphocytes
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11
Q

What cells produce immunoglobulins and what cells are they derived from?

A
  • Plasma cells
  • These are derived from B lymphocytes
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12
Q

What are the two chains in an immunoglobulin? Draw their positions and how they are joined.

A
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13
Q

What two enzymes can be used to digest immunoglobulins and what fragments do they break down into?

A
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14
Q

What are the different domains in an immunoglobulin? [EXTRA?]

A

Note: The subscript just stands for light or heavy, so there are V and C domains.

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15
Q

What types of molecules are immunoglobulins?

A

Glycoproteins

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16
Q

Are immunoglobulins soluble?

A

Yes

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17
Q

What secondary structures are found in antibodies?

A

Beta sheets

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18
Q

Where are the hypervariable regions of immunoglobulins?

A

There are variable regions at the ends of the light and heavy chains.

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19
Q

What are the hypervariable regions in antibodies also known as?

A

Complementarity determining regions (CDRs)

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20
Q

Draw the different functional parts of an immunoglobulin (antibody).

A
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21
Q

What are the different classes and subclasses of immunoglobulins?

A
  • IgM
  • IgG -> IgG1, IgG2, IgG3, IgG4
  • IgD
  • IgA
  • IgE
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22
Q

For each immunoglobulin class, state whether they are monomers, dimers, etc.

A
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23
Q

For each immunoglobulin (antibody) class, state the symbol, molecular size and concentration (mg/ml).

A
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24
Q

For each immunoglobulin (antibody) class, state whether it is/has:

  • Involved in the classical pathway of complement activation
  • Transferred via the placenta
  • Low affinity binding to phagocytes
  • High affinity binding to macrophages and activated neutrophils
  • High affinity binding to basophils or mast cells
A
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25
Q

How many binding sites for antigens does each class of antibody have? [IMPORTANT]

A
  • IgG = 5
  • IgM = 10
  • IgD = 14
  • IgA = 12
  • IgE = 12
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26
Q

Explain the concepts of affinity and avidity.

A
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27
Q

Which immunoglobulin class is the first to be produced by B lymphocytes? What is its affinity and avidity?

A
  • IgM
  • It has:
    • Low affinity
    • High avidity (overall strength of binding between an antibody and an antigen)
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28
Q

Which immunoglobulin class protects the mucosa?

A

IgA

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29
Q

What are the two main regions of immunoglobulins? Which is variable and which is constant?

A
  • Fab (variable)
  • Fc (constant)
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30
Q

What does the Fab region of an immunoglobulin do?

A

It is the region that binds to the antigen.

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31
Q

What does the Fc region of an immunoglobulin do?

A
  • Complement activation
  • Binding to receptors on different cell types:
    • Macrophages and neutrophils -> Triggers phagocytosis and activation
    • Mast cells -> Triggers degranulation
    • Epithelial cells -> This causes the immunoglobulin to be secreted into tears, saliva etc.
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32
Q

What are the different types of immunoglobulin based on their affinity for the receptor for the Fc region? What is the function of each?

A
  • High affinity-Ig
    • Often pre-bound to receptor (since the affinity is high)
    • Waits for antigen to come along
  • Low affinity-Ig
    • Fc receptor not normally occupied
    • The receptors are only occupied after antibody has become complexed to an antigen (useful in phagocytosis)
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33
Q

Which immunoglobulin class binds to mast cells?

A

IgE

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34
Q

Which immunoglobulin classes are secreted into:

  • Tears
  • Saliva
  • Colostrum
  • Gut
  • Across placenta
A
  • Tears, Saliva, Colostrum, Gut -> IgA
  • Across placenta -> IgG
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35
Q

Give an example of a high affinity immunoglobulin.

A

IgE on mast cells

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36
Q

Give an example of a low affinity immunoglobulin.

A

IgG, IgA, IgE

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37
Q

What are some positive and negative actions of mast cells?

A
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38
Q

What are some ways in which immunoglobulins can cause disease via mast cells?

A

They bind to them and activate them, causing a range of symptoms.

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39
Q

What is opsonisation?

A

The process by which a pathogen is marked for destruction by antibody-dependent cellular cytotoxicity, antibody-dependent cellular phagocytosis or complement-dependent cytotoxicity.

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40
Q

Which cell types do immunoglobulins activate to phagocytose (opsonisation)?

A

Neutrophils and neutrophils

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41
Q

Describe how immunoglobulins cause opsonisation.

A
  • The antibodies assemble giving rise to a zipper mechanism that sinks into the cytoplasm
  • Closure by plasma membrane fusion
  • Actin cytoskeleton assembly is essential
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42
Q

How do immunoglobulins protect against viruses?

A

They bind to the virus and prevent its entry into the cell.

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43
Q

What are the different roles of antibodies (immunoglobulins)? [IMPORTANT]

A
  • Bind to microorganisms and prevent their entry into body/cells
  • Bind to organisms and bind also to phagocytes
  • Opsonisation (assisting with phagocytosis) + Activate phagocytes
  • Neutralise bacterial toxins
  • Activate complement pathway and induces inflammation
  • Membrane-bound form is found on B lymphocytes and acts as a receptor
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44
Q

What are plasma cells derived from?

A

B-lymphocyte

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45
Q

In what locations do plasma cells produce immunoglobulins?

A
  • Gut
  • Mammary gland
  • Lymphoid organs
  • Bone marrow
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46
Q

What is a hybridoma? [EXTRA?]

A
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47
Q

What are some uses of monoclonal antibodies?

A
  • Diagnostic agents (histology, immunoassays)
  • Experimental probes for cell biology
  • Therapeutic agents
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48
Q

Draw the process of antibody engineering.

A
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49
Q

What is the complement system?

A
  • A part of the immune system that enhances (complements) the ability of antibodies and phagocytic cells to clear microbes and damaged cells from an organism, promote inflammation, and attack the pathogen’s cell membrane.
  • According to spec: System of neutral proteinases secreted into plasma by the liver (also by macrophages).
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50
Q

Is the complement system part of the adaptive or innate immune system?

A
  • It is part of the innate immune system, so it does not change throughout the lifetime.
  • The complement system can, however, be recruited and brought into action by antibodies generated by the adaptive immune system.
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51
Q

What is the complement system an example of?

A

An example of a triggered enzyme cascade .

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52
Q

What are the 3 ways in which the complement pathway allows response to an infection?

A
  • Opsonisation (marking) of particles for phagocytosis
  • C5a as a chemoattractant
  • Membrane attack Complex (MAC).
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53
Q

What do complement system defects lead to?

A

They predispose to bacterial infections (e.g. C3 deficiency).

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54
Q

What does inappropriate complement activation lead to?

A

Lupus

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55
Q

What is the key component on the complement system and how is it generated? [IMPORTANT]

A
  • C3b, which is generated by the cleavage of C3.
  • The enzymes that do this are called C3 convertases.
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56
Q

What are the 3 steps to complement activation?

A
  1. Generation of C3 splitting enzymes (‘convertases’)
  2. Cleavage of complement protein C3
  3. Terminal lytic events (‘MAC attack’)
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57
Q

What are the three pathways that can activate the complement system?

A
  • Classical pathway
  • MBP lectin pathway
  • Alternative pathway
58
Q

Draw a summary of the activation and outcomes of the complement system.

A
59
Q

What is the classical pathway of complement activation and how does it work?

A

It is the pathway that links the antibody response to innate immunity (i.e. antibodies bind to antigens triggers the complement system):

  • C1q binds to antibody-antigen complexes
  • Six molecules of C1q associated with C1r and C1s
  • C1q binding causes C1r to cleave C1s to an active form
  • C1s cleaves C4 and C2 to generate C4b and C2b*
  • C4b2b is an active C3 Convertase

The C3 convertase can cleave C3 to C3b, which is the key component of the complement pathway.

60
Q

What is the alternative pathway of complement activation and how does it work?

A

It is the pathway that activates the complement system when there is no antibody to trigger it (like in the classical pathway):

  • Complement component C3 is an abundant plasma protein
  • Initiated by spontaneous hydrolysis of C3 (‘tickover’)
    • C3b molecule binds factor B and then this complex binds factor D
    • This cleaves factor B to give Ba and Bb
    • The C3b-Bb complex is the alternative pathway C3 convertase which can then produce many C3b molecules from C3 molecules
61
Q

What makes C3b the most important component of the complement system?

A

C3b has a thioester bond which once activated can bind covalently to surface proteins & carbohydrates.

62
Q

What is the MBP lectin pathway of complement activation and how does it work?

A

It is the pathway that activates the complement system after MBP binds to bacteria:

  • MBP (aka MBL) is a plasma protein that binds to bacteria
  • Serine proteinases MASP-1 and MASP-2 bind to the MBP
  • These convert C4 into C4a and C4b, as well as C2 into C2a and 2b
  • The end result of this is generation of C4b2b, which is the C3 convertase that can cleave many C3 molecules into C3b molecules
63
Q

What is the main chemoattractant in the complement system and what type of molecule is it?

A

C5a (as well as C3a and C4a) -> Anaphylotoxins

64
Q

Describe how C5a is formed and how it acts as a chemoattractant.

A
  • C3b + C3 convertase form C5 convertase, which makes C5a and C5b
  • C5a acts through a G protein coupled receptor (GPCR) on:
    • Endothelial cells
    • Mast cells smooth muscle cells (SMCs)
    • Phagocytes
  • It causes activation, contraction and chemotaxis.
65
Q

What are the main opsonins (involved in opsonisation) of the complement system?

A

C3b and C4b

66
Q

Describe how C3b and C4b act as opsonins in the complement system.

A
67
Q

What is MAC and how does it work?

A
  • Membrane Attack Complex
  • It is one of the 3 main ways in which the complement pathway kills pathogens
68
Q

Why don’t host cells activate the complement system?

A
  • C1INH inhibits the first steps of classical pathway activation by dissociating C1s and C1r from C1q.
  • C4BP and factor H make C4b and C3b susceptible to enzymatic cleavage and inactivation by factor I.
  • Host cell membranes inactivate C3 convertases via DAF, MCP and CR1 and factor I.
  • Host CD59 prevents assembly of the membrane attack complex.
69
Q

Explain some complement system deficiencies. [EXTRA]

A
70
Q

What is haemostasis?

A

The process that prevents excessive blood loss:

  • Vascular injury
  • Platelet Plug Formation
  • Blood Clotting (Coagulation)
  • Keeping the clot localised
  • Removing clots (Fibrinolysis)
71
Q

How does arterial muscle respond to arterial damage?

A
  • Arterial injury causes arterial smooth muscle contraction
  • Arterial contraction lowers downstream blood pressure
  • Initial trigger is trauma, and then later maintained it is by platelets
72
Q

What is vasospasm?

A

The narrowing of the arteries caused by a persistent contraction of the blood vessels, which is known as vasoconstriction. This narrowing can reduce blood flow.

73
Q

What are the two key mediators for arterial muscle contraction after arterial injruy?

A

Serotonin and Thromboxane A2

74
Q

Describe the formation of a platelet plug in response to arterial injury.

A
75
Q

What are platelets?

A

Small cytoplasmic fragments of megakaryocytes

76
Q

What is the size of platelets?

A

2-5µM

77
Q

What is the lifespan of platelets in the blood?

A

8-10 days

78
Q

What is the concentration of platelets in the blood?

A

4 x 108 per ml

79
Q

Can platelets be activated?

A

Yes, they are activated by a range of molecular interactions.

80
Q

What are some general functions of platelets?

A
  • Secrete important smooth muscle cell (SMC) growth factors -> Esp. platelet derived growth factor (PDGF)
  • Secrete vasoactive mediators (TxA2, 5-HT) -> e.g. For vasoconstriction upstream of a clot
  • Play a key role in endothelial cell repair
81
Q

What are the main molecules found in platelet granules?

A
  • ADP
  • 5-HT
82
Q

How do platelets play a role in homeostasis?

A
  • Platelets adhese to vessel wall
  • Platelets aggregate together to form a plug
  • Release granule contents
    • Cause vasoconstriction upstream
    • Cause platelet aggregation
  • Provide co-factors for clotting
  • Initiate vascular and other repair processes
83
Q

How do platelets adhese to damaged endothelial and sub-endothelial cells?

A
  • Platelet GP Ia binds Collagen
  • Platelet GP Ib binds Von Willebrand factor (vWf)

Note: GP = Glycoprotein

84
Q

How do platelets aggregate?

A
  • Fibrinogen ‘bridges’ stabilise platelet aggregates
  • Fibrinogen binds platelet surface GPIIb/GPIIIa
  • Key mediators of aggregation are ADP & TxA2
85
Q

What are the key mediators of platelet aggregation?

A

ADP and TxA2

86
Q

State the function of these different molecules released by platelets:

  • 5-HT
  • ADP
  • PDGF
  • TxA2
A
  • 5-HT -> Vasoactive mediator (causes vasoconstriction upstream of the injury)
  • ADP -> Mediates platelet aggregation
  • PDGF -> Promotes smooth muscle growth
  • TxA2 -> Vasoactive mediator (causes vasoconstriction upstream of the injury) + Mediates platelet aggregation
87
Q

What does PDGF stand for?

A

Platelet derived growth factor

88
Q

What are the different glycoproteins on a platelet and what are the functions does each have?

A

Involved in adhesion:

  • GP Ia binds Collagen
  • GP Ib binds Von Willebrand factor (vWf)

Involved in aggregation:

  • GP IIb / GP IIIa bind to fibrinogen
89
Q

What are some platelet disorders?

A
90
Q

What happens after platelets form a primary plug following arterial injury?

A

Fibrin assembles within the plug to form a blood clot.

91
Q

In blood clotting, what monomers are converted into what polymer?

A

Fibrinogen monomers are converted into fibrin strands.

92
Q

What enzyme is responsible for converting fibrinogen to fibrin?

A

Thrombin

93
Q

What is the inactive form of thrombin?

A

Prothrombin

94
Q

Describe the principle on which blood clotting works.

A

It involves a series of proteases that, when activated, act on one another sequentially to ultimately produce insoluble fibrin.

95
Q

What are the 3 parts of the blood clotting pathway?

A
  • There is the common pathway
  • This is fed into by either the intrinsic or extrinsic pathway
96
Q

What are the two types of fibrin clot and how can they be interconverted?

A

Fibrin loose clot can be converted to a tight clot by factor VIIIa.

97
Q

How are different blood coagulation factors symbolised?

A
  • They are given Roman numerals
  • e.g. Prothrombin is II
98
Q

What are the 4 major blood coagulation factors mentioned in the spec and what is the active form of each?

A
  • Tissue factor (active)
  • Factor VIII
    • Factor VIIIa when active
  • Prothrombin (II)
    • Thrombin (IIa) when active
  • Fibrinogen (I)
    • Fibrin (Ia) when active
99
Q

What activates the intrinsic and extrinsic pathway of blood clotting?

A
  • Intrinsic -> Negatively charged surface
  • Extrinsic -> Tissue and vessel damage
100
Q

Draw a summary of how the 3 pathways of blood clotting are connected.

A
101
Q

Draw out the whole blood clotting pathway in detail.

A
102
Q

Draw out a simplified full pathway of blood clotting.

A
103
Q

Summarise the common pathway of blood clotting.

A
  • Factor X is converted to Factor Xa by either:
    • Factors VIIIa and IXa, Platelet phospholipid and Ca2+ (Intrinsic pathway)
    • Tissue factor XIIa and Ca2+ (Extrinsic pathway)
  • Factor Xa now, along with factor Va and Ca2+ converts prothrombin (II) to thrombin (IIa)
  • Thrombin converts fibrinogen into fibrin, which is in a loose clot
  • The loose clot is turned into a tight clot by factor XIIIa
104
Q

Show how positive feedback occurs in the common pathway of blood clotting.

A
105
Q

How are platelets involved in the common pathway of blood clotting?

A
  • The conversion of prothrombin to thrombin, using factors Xa and Va, as well as Ca2+ occurs on the phospholipid membrane of a platelet
  • The conversion of factor X to Xa using Ca2+ and factors VIIIa and IXa from the extrinsic pathway occurs on the phopholipid membrane of a platelet
106
Q

Which blood coagulation factor is fibrinogen?

A

Factor I

107
Q

Where is fibrinogen made?

A

Liver

108
Q

How many polypeptides are in fibrinogen?

A

6 polypeptides (α2β2γ2)

109
Q

How is fibrinogen turned into a fibrin clot?

A
  • Thrombin removes negatively charged fibrinopeptides
  • Without the fibrinopeptide domains, fibrin aggregates
  • This is a loose clot
  • Fibrin is then crosslinked at Gln and Lys residues by Factor XIIIa, forming a tight clot
110
Q

What are some diseases to do with fibrinogen?

A
111
Q

Which coagulation factor is prothrombin?

A

Factor II

112
Q

How is prothrombin post-translationally modified? [EXTRA]

A
  • Amino terminus is post-translationally modified
  • Glutamate is γ-carboxylated (Gln -> Gla)
  • Catalysed by a vitamin K-dependent enzyme
113
Q

What does prothrombin require for activation to thrombin?

A
  • Prothrombin binds calcium binds platelet phospholipid
  • Colocalisation with Factors Xa & Va on platelet membrane
  • Colocalisation -> 10, 000x increase in rate of cleavage
114
Q

What are serine proteases?

A
  • Active forms of Factors II, VII, IX, X, XI & XII are serine proteases
  • (i.e. IIa, VIIa, etc.)
  • The previous serine protease cleaves the next one to activate it
115
Q

What are the different substrates of thrombin?

A
  • Fibrinogen (Factor I)
  • Factor XIII (Fibrin-stabilising factor)
  • Factor V
  • Factor VIII
  • Factor XI
116
Q

Draw a summary of the intrinsic pathway of blood clotting.

A
117
Q

What is the crucial modifier that speeds up the intrinsic pathway of blood clotting?

A

Factor VIIIa increases the rate of the conversion of factor X to Xa 200, 000-fold.

118
Q

How does positive feedback happen in the intrinsic pathway of blood clotting?

A

Thrombin increases the conversion of VIII -> VIIIa

119
Q

What is haemophilia and how is it related to the blood clotting pathways?

A
120
Q

Draw a summary of the extrinsic pathway of blood clotting and how it feeds into the common pathway.

A
121
Q

Is the extrinsic short or long-lived? What is it responsible for?

A
  • Short-lived
  • It is primarily responsible for initiating blood clotting
122
Q

What parts of the extrinsic pathway can be inhibited? By what?

A

Extrinsic pathway inhibitor (EPI) (a.k.a TFPI) blocks the conversion of factor X to Xa via EP.

123
Q

What type of molecule is EPI?

A

A lipoprotein that circulates in the blood and inhibits the conversion of factor X to Xa in the extrinsic pathway.

124
Q

Draw all the ways in which blood clotting can be regulated.

A
125
Q

What are some natural inhibitors of blood clotting?

A
  • Blood Flow
  • EPI (Extrinsic Pathway Inhibitor) (aka TFPI)
  • Anti thrombin III (ATIII)
  • Thrombomodulin (TM)
  • Activated protein C (APC)
126
Q

What is ATIII?

A
  • Anti Thrombin III
  • It is an inhibitor of thrombin, so it inhibits blood clotting
127
Q

Where is anti thrombin III (ATIII) produced?

A

Endothelial cells & the liver

128
Q

What is the ATIII-thrombin interaction stabilised by?

A
  • Heparin
  • Endothelial cells express ‘heparin-like molecules’
129
Q

What are serpins? GIve some examples.

A
  • Serine protease inhibitor
  • They inhibit the action of serine proteases (which are the active forms of coagulation factors II, VII, IX, X, XI & XII) so they prevent clotting
  • Examples:
    • Anti thrombin III (ATIII)
    • Alpha 1 anti trypsin (AAT)
    • Complement C1q inhibitor
    • Plasminogen activator inhibitor-1 (PAI-1)
130
Q

What is fibrinolysis?

A

The breakdown of a blood clot.

131
Q

What is the key enzyme for breaking down fibrin in blood clots?

A

Plasmin

132
Q

What type of enzyme is plasmin?

A

Serine protease

133
Q

Describe the activation of plasmin.

A
  • Plasmin circulates as inactive plasminogen
  • Plasminogen activators generate plasmin
134
Q

What are some examples of problems associated with haemostasis?

A
135
Q

Describe briefly the metabolism of haem.

A
  • Originates from red blood cells
  • Converted to billirubin
  • Transported to the liver bound to albumin
  • Conjugated in the liver to make it water-soluble
  • Excretion of bilirubin
136
Q

What do elevated levels of bilirubin often indicate?

A

Elevated levels may indicate liver damage or disease.

137
Q

What can inhibit the action of vitamin-K-dependent clotting factors (serine proteases)?

A

Proteins produced in the liver, namely a-1-antitrypsin.

138
Q

What is the function of lipoproteins?

A

They act as transport vehicles for lipids.

139
Q

Where are lipoproteins (like LDL) produced?

A

In the liver.

140
Q

Where are LDL receptors found and how are they regulated?

A

They are primarily found on the liver. When the cholesterol content of hepatocytes is raised by ingestion of diets high in saturated fat and cholesterol, LDL receptors fall and plasma LDL levels rise.

141
Q
A

YEAR 1 - Biochemistry and Medical Genetics (Anton) (8 decks)

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