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InF - immune system > L3 - defence against infection > Flashcards

L3 - defence against infection Flashcards

1
Q

infections can be ……

A

intracellular or extracelular

Intra require require cell-mediated immunity (T cells, NK cells)
- eliminate infected cells or activate macrophages to kill pathogens hiding within vesicles

extra - humoral response, antibodies,complement and phagacytosis

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2
Q

mechanism of ‘drinking in antigens’ by dendritic cells

A

pinocytosis
long projections maximise SA

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3
Q

estimated volume of mucosal surfaces in body that need protection

A

200m2

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4
Q

name the 3 types of complement pathway and where they work

A

alternative pathway - on pathogen surface

mannose-lectin binding pathway - lectin on pathogen surface

classical pathway - antigen:antibody complex

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5
Q

why is the complement pathway named this and what is it

A

Helps the system fight infection “complimenting” work oif immune system

made up of zymogens (inactive enzymes) that cause a cascade each cleaving and activating the next

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6
Q

where are the complement proteins/zymogens produced

A

liver

by hepatocytes then released into blood stream

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7
Q

describe the ALTERNATIVE complemnet pathway - detail

A
  1. C3 is spontaneously cleaved in serum by tick over activation = C3a and C3b
  2. C3b binds covalently via thioester bond to bacterial membrane
  3. Factor B binds to C3b but hydrolysed by factor D = C3bBb + Ba
  4. C3bBb is a C3 convertase = more C3a and C3b
  5. when 2 of these convertases dimerise forms a C5 convertase = (C3b)2Bb = produces C5a + C5b
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8
Q

what do all pathways lead to

A

a C3 convertase

= complement activation

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9
Q

functions of complement activation

A
  1. recruitment of inflamatory cells
  2. opsonisation of pathogens
  3. direct killing by MATC
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10
Q

factors involved in alternative complement pathway

A

C3
B
D

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11
Q

factors involved in mannose-lectin pathway

A

MBL
MASP-1
MASP-2
C4
C2

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12
Q

factors involved in classical pathway

A

C1q
C1r
C1s
C4
C2

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13
Q

which factors do classical and MB pathway have in common but NOT alternative

A

C4
C2

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14
Q

what is Mannose-binding lectin and what conc is it usauly found at

A

MBL is a protein found at low concentrations in blood normally

  1. when macrophages ingest bacteria they produce interleukin-6 = IL-6
  2. triggers hepatocytes in liver to prouce acute-phase proteins = MBL
  3. MBL binds to terminal mannose sugars on bacterial surfaces
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15
Q

what does MBL bind to in complement pathway and how does it do this

A

terminal mannose sugars on bacterial surface

MBL monomers form trimers with mannose recognition domains

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16
Q

describe the MBL complement pathway -detail

A
  1. MBL binds to mannose residues on bacterial surface
  2. MASP proteases (MBL-acsociated-proteases) cleave C4 and C2 in the protein
  3. C4b binds to bacterial surface and acsociates with C2a = C4bC2a
  4. C4bC2a is a C3 convertase
  5. the C3b produced by cleave of C3 ascociates with the C3 convertase produces a C5 convertase

C4bC2a + C3b = C4bC2aC3b

17
Q

what don ficcolins do relative to the MBL complement pathway

A

bind ton acetelyated sugars onbacterial surface instead of mannose

via fibronectin domains BUT also activated MASPs to cleave C2 and C4

= exactly the same except from what it binds to

18
Q

what does the C3 concertase at the end of the activatiting the complement pathways do - 3 different parts

A
  1. C3a and C5a:
    peptide mediators of inflammation - phagocyte recruitment
  2. C3b:
    binds to complement receptors on phagocytes

opsonisation of bound pathogens

  1. MAC - Membrane-Attack-Complex

other complemts come togther to from lysis cauysing complex

19
Q

facrtors nincolved in forming the membrane attack complex

A

C5b
C6
C7
C8
C9

20
Q

formation of membrane attack complex

A
  1. C5b binds to C6 + C7 = C5b67
  2. complex binds to membrane of pathogen or cell via C7
  3. C8 binds to complex and inserts itself INTO the cell membrane
  4. C9 binds to complex and polymerises = fortming a pore in membrane
  5. Death of cell due to osmosis
21
Q

defects in the complemnet pathway can cause what - C3 defect

A

C3 defects cause pyogenic indeftions
- staph and stept infections
- pus forming

= highlights C3 importance in opsonisation of bacteria

InF - immune system (6 decks)

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