Innate vs. Adaptive Immunity Flashcards

1
Q

What is the body’s first line of defence against invading pathogens?

A

The innate immune system.

Physical barriers first, then chemical and biological barriers.

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2
Q

Why are the complement proteins found in the bloodstream?

A

Because they are soluble proteins

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3
Q

What is the overall aim of complement proteins?

A

To destroy invading pathogens

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4
Q

What is opsonisation?

A

The process of the complement proteins coating the outer surface of the pathogen which allows phagocytes and macrophages to engulf the pathogen.

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5
Q

Why does opsonisation make it easier for macrophages to engulf pathogens?

A

Because macrophages have special receptors for specific complement proteins.

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6
Q

What is the process of making a membrane attack complex?

A

A group of complement proteins makes a hole in a pathogen, which causes inrushing fluids, creating an imbalance in osmolarity and causes the pathogen to lyse and be destroyed.

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7
Q

What are the 3 main functions of complement proteins?

A
  1. Opsonisation
  2. Making a membrane attack complex
  3. Enhancing inflammation
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8
Q

Where are complement proteins produced?

A

Produced in the liver, then travel through the bloodstream.

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9
Q

Which form do the circulating complement proteins take and when and why does this change?

A

Complement proteins circulate in an inactive form and therefore they don’t attack self.

When they discover a pathogen, they become activated.

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10
Q

What are the 3 complement pathways?

A
  1. Classical pathway
  2. Alternative pathway
  3. Lectin pathway
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11
Q

Which complement proteins are involved in the classical pathway?

A
  • C1q
  • C1r
  • C1s
  • C4
  • C2
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12
Q

Which complement proteins are involved in the alternative pathway?

A
  • Factor D
  • Factor B
  • Properdin
  • C3
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13
Q

Which complement proteins are involved in the lectin pathway?

A
  • MBL
  • Ficolin
  • MASP-2
  • C4
  • C2
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14
Q

What is the main purpose of all the proteins involved in the classical, alternative and lectin pathways?

A

To help in splitting / activating complement protein 3 to make C3a and C3b.

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15
Q

What is the main function of C3a?

A

C3a, together with other proteins enhances inflammation

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16
Q

What is the main function of C3b?

A

C3b initiates opsonisation, and lysis of the cell to create a membrane attack complex.

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17
Q

How does the classical pathway activate C3 (by cleaving it into C3a and C3b)?

A
  • The classical pathway gets initiated / activated when antibodies bind to the antigen of a pathogen.
  • When this happens, some complement proteins composed of C1q, C1s and C1r bind to the antibodies.
  • What the C1q-C1s-C1r complex does is form another complement protein complex known as C4b2a complex. Another name for this is C3 convertase (because it is also an enzyme).
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18
Q

How does the classical pathway activate C3 (by cleaving it into C3a and C3b)?

A
  • The lectin pathway is initiated by proteins binding to carbohydrates on te pathogen.
  • For example, a protein called ficolin binds to the oligosaccharides on a pathogen.
    • Ficolin also has other proteins bound to it - MASP1 and MASP2.
  • Mannose-binding-lectin (MBL) binds to mannose parts of the pathogen.
    • MBL also has other proteins bound to it - MASP1 and MASP2.
  • Ficolin and MBL, together with the MASPs, form a complement protein complex, exactly the same as the classical one: C4b2a complex (C3 convertase).
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19
Q

How does the alternative pathway activate C3 (by cleaving it into C3a and C3b)?

A
  • The alternative pathway becomes activated when the classical pathway and lectin pathway forms C4b2a complex.
  • C4b2a complex splits C3 into C3a and C3b. The alternative pathway is initiated with the C4b2a complex activates C3b.
  • This C3b then binds to the surface of the pathogen.
  • The alternative pathway then forms another type of C3 convertase, different to the one formed by the classical and lectin pathways.
  • This C3 convertase is called C3bBb complex (C3 convertase).
  • The alternative pathway can also form another type of C3 convertase with a protein called properin. It is known by the same name (C3bBb complex which is a C3 convertase).
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20
Q

What is the function of C4b2a?

A

It splits C3 into active forms: C3a and C3b.

21
Q

What does C3a do?

A

C3a, along with other complement proteins (such as C5a, which is one of the most important complement proteins) enhances inflammation.

22
Q

What does C3b do?

A

C3b initiates opsonisation and initiates the formation of the membrane attack complex.

23
Q

What is the joint action of C3a and C5a?

A

Stimulation of mast cells to create histamine.

24
Q

What does histamine do?

A

It enhances inflammation. It increases vascular permeability which allows leukocytes to pass through more easily. Histamine also attracts leukocytes.

25
Q

Which kind of bond is formed between C3b and a pathogen?

A

Thioester bond

26
Q

What is the name of the process where many C3bs form thioester bonds with the pathogen surface, coating the pathogen?

A

Opsonisation

27
Q

Which complement protein is enlisted to help C3b engulf pathogens?

A

C5a

28
Q

Why is C5a needed for C3b to phagocytose a pathogen?

A
  • When C5a binds to the C5a receptor of a macrophage, this allows the macrophage to bind to the C3b protein through the CR1 receptors.
  • Through this, the macrophage can phagocytose the pathogen.
29
Q

C3b can opsonise and form the membrane attack complex. What is its alternative function?

A

C3b can alternatively bind to the C4b2a complex. When it binds it forms the C4b2a3b complex. This is also known as C3/C5 convertase.

30
Q

What are the 2 functions of C3/C5 convertase?

A
  • Cleave and activate C3 to form C3a and C3b
  • Cleave and activate C5 to form C5a and C5b
31
Q

What are the functions of C5a?

A
  • Enhancing inflammation
  • Binding to the macrophage receptor
32
Q

What is the function of C5b?

A

Initiating the terminal stage - the formation of the membrane attack complex (MAC).

C5b, together with other complement proteins of a higher number (C7, C8, C9) will form the MAC.

33
Q

What does the formation of a membrane attack complex cause?

A

The formation of a MAC on the surface of a pathogen will cause the pathogen to lyse and burst.

34
Q

Which basic cell does the adaptive immune system start with?

What does this cell give rise to?

A

Progenitor lymphoid cell.

Either naive B cells or naive T cells.

35
Q

What happens to a naive T cell if its receptors recognise a self-antigen?

A

The naive T cell will be destroyed before it matures

36
Q

Which kind of receptors do naive T cells have when they are developed from a progenitor lymphoid cell?

What happens when they mature, proliferate and differentiate?

A

They have CD4 and CD8 co-receptors.

They either become a naive CD4 T cell with a T cell receptor, or a naive CD8 T cell with a T cell receptor.

37
Q

What happens to the naive CD8 T cell?

A
  • It becomes activated when an infected antigen presenting cell, such as a phagocyte, presents an antigen on an MHC1.
  • This will activate the naïve CD8 T cell to become a CD8 cytotoxic T cell.
  • Cytotoxic T cells destroy infected cells with the same specific antigen which was presented by the infected phagocyte.
  • Activated CD8 T cells kill infected cells.
38
Q

What happens to the naive CD4 T cell?

A
  • It becomes activated when a non-infected antigen presenting cell, such as a phagocyte, presents a foreign antigen on an MHC2.
  • This CD4 T cell only recognises a specific foreign antigen. When it recognises this specific antigen it becomes activated through the MHC2.
  • The naïve CD4, when activated, becomes a T helper cell.
  • The main goal of a T helper cell is to enhance the immune response by activating B cells, natural killer cells, macrophages and other phagocytes.
39
Q

What is the main goal of a T helper cell?

A

The main goal of a T helper cell is to enhance the immune response by activating B cells, natural killer cells, macrophages and other phagocytes.

40
Q

What happens to the naive B cells?

A
  • Naïve B cells have antibodies from when they became naïve B cells derived from the progenitor lymphoid cell.
  • The naïve B cell antibodies can recognise specific antigens of a pathogen.
  • This cause the naïve B cell to engulf the pathogen, then process it, then present the foreign antigen on an MHC2 to the activated T helper cell.
  • The activated T helper cell can then activate the B cell to proliferate and to differentiate into either a memory B cell or a plasma cell.
  • Plasma cells secrete specific antibodies towards the antigen.
  • Memory B cells form memory of that specific antigen so that the next infection by the same antigen can be resolved quickly.
41
Q

What is the function of plasma cells?

A

Plasma cells secrete specific antibodies towards the antigen.

42
Q

What is the function of memory B cells?

A

Memory B cells form memory of that specific antigen so that the next infection by the same antigen can be resolved quickly.

43
Q

What is the function of antibodies secreted by plasma cells?

A
  • Neutralise a pathogen
  • Opsonise a pathogen
  • Complement activation
44
Q

How do antibodies secreted by plasma cells neutralise a pathogen?

A

Given a healthy cell and a bacterium which is about to kill the healthy cell, antibodies can bind onto the antigen and neutralise it, preventing bacterial adhesion.

45
Q

How do antibodies secreted by plasma cells opsonise a pathogen?

A

Antibodies opsonise the bacteria. They coat the bacteria so phagocytes can engulf it. Opsonisation promotes phagocytosis.

46
Q

How do antibodies secreted by plasma cells activate complement?

A

Specific antibodies acting towards a specific antigen can activate complement.

This means that the antibodies can opsonise the pathogen, promoting phagocytosis, as well as lysing the pathogen.

47
Q

Describe how antibodies are comprised.

A

Antibodies consists of a variable region on the N terminal and a constant region on the C terminal.

48
Q

What part of the antibody determines its class?

A

The constant region

49
Q

What is the name of the site within an antigen which is recognised by the antibody?

A

Epitope