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cellular basis of immunity > 5 - antibody structure and function > Flashcards

5 - antibody structure and function Flashcards

1
Q

humoral immunity

A

involves soluble substances
mediated by macromolecules in extracellular fluid
e..g secreted antibodies, complement proteins, antimicrobial peptides

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2
Q

antibody defn

A

host protein produced in response to the presence of foreign molecules in the body

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3
Q

antibodies produced by

A

plasma cells

lymphoid lineage

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4
Q

B cell effector cells

A

antibodies

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5
Q

antibody-antigen complex

A

antibodies bind to Fc regions of antigens and opsonise the cells

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6
Q

linus pauling 1940s importance

A

interested in antibody polypeptide structure and its ability to recognise antigens
proposed one immunoprotein that changed its conformation

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7
Q

clonal selection for self tolerance

A

B cells producing antibodies against self antigens are tested and deleted

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8
Q

clonal expansion

A

B cells producing correct specific antibody for the target antigen is activated and multiplied

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9
Q

B cells after infection is over

A

become memory cells and wait in lymphatics

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10
Q

antibodies are

A

glycoproteins

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11
Q

shared functional properties of antibodies

A

all bind to both antigens and immune cells

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12
Q

shared structural properties of antibodies

A

all have Y shaped unit

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13
Q

where do antibodies bind to on an antigen

A

epitope

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14
Q

epitope

A

amino acid sequence on a polypeptide coat protein

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15
Q

paratope

A

antigen-binding region of antibody

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16
Q

where do antigens bind to on an antibody

A

paratope

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17
Q

features of antibody antigen binding

A

reversible
non-covalent

antibodies can change places for a better fit

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18
Q

CDR

A

complementarity determining region

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19
Q

describe structure of an antibody

A

4 polypeptide chains

held together by disulphide bridges and non-covalent bonds

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20
Q

importance of hinge region of antibody

A

enables contortion allowing binding

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21
Q

importance of CDRs

A

hypervariability regions

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22
Q

porter (1959) and Edelman (1961)

A 
worked on structure of IgG
used enzymes to break up antibody  (papain cleavage and pepsin cleavage)
3 fractions (Fab) showed that there were 4 polypeptides
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23
Q

classes of immunoglobulin

A 
IgG
IgM
IgA
IgE
IgD
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24
Q

how are classes of immunoglobulin distinguished

A

by their number of y-units

by their type of heavy chain polypeptide

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25
Q

how many types of light chain polypeptide are there

A

2

26
Q

no of light chains =

A

no of heavy chains

27
Q

subclasses of IgG

A

IgG1
IgG2
IgG3
IgG4

28
Q

valency of 2

A

2 potential binding sites to target antigen

29
Q

IgM

A

first response
low affinity binding
(hypermutation of B cell receptor causes class to switch to IgG)
pentameric –> 5 Y units

30
Q

IgG

A

secondary response
principal antibody –> high serum concentration
heavy chain = gamma

31
Q

IgA

A

protects mucous membranes
secreted in breast milk and other secretions (tears, mucous, saliva)
heavy chain = alpha

32
Q

IgE

A

protects against parasites and allergies

Fc receptors on mast cells, basophils, eosinophils

33
Q

J chain

A

holds 5 Y components to make pentameric IgM

34
Q

M cells

A

relay info to DCs

35
Q

subclasses of IgG

A

IgG1
IgG2
IgG3
IgG4

36
Q

valency of 2

A

2 potential binding sites to target antigen

37
Q

IgM

A

first response
low affinity binding
(hypermutation of B cell receptor causes class to switch to IgG)
pentameric –> 5 Y units

38
Q

IgG

A

secondary response

principal antibody –> high serum concentration

39
Q

IgA

A

protects mucous membranes

40
Q

IgE

A

protects against parasites

41
Q

J chain

A

holds 5 Y components to make pentameric IgM

42
Q

M cells

A

relay info to DCs

43
Q

transcytosis

A

movement of antibody across the epithelium into the lumen side of the gut

movement stimulated by docking of antibody to polymeric Ig receptor (with secretory component) on epithelial cell

44
Q

describe release of IgA after transcytosis into gut

A

protease cleaves the Ig receptor near the membrane

IgA - secretory component - polymeric Ig receptor complex

45
Q

role of secretory component

A

protects and anchors antibody complex at desired location

so phagocytic cell can bin to the Fc receptor and destroy

46
Q

Fc receptor

A

found on immune cells
binds to Fc component of antibodies that are attached to pathogenic cells
binding triggers phagocytosis

47
Q

ITAM

A

immunoreceptor tyrosin-based activation motif

important signalling molecule

48
Q

lectin activation pathway of complement

A

recognition and binding of carbohydrates by collectins

e.g. ficolin or mannose-binding lectin is a collecting that binds to mannose on the surface of a pathogen

C4 and C2 components are cleaved
C2a and C4b bind to form classical C3 convertase on pathogen cell membrane

49
Q

classical activation of complement

A

triggered by antibody binding to antigen or pentraxins
antibody-antigen complex forms

series of proteins form C3 convertase
cleaves C3 protein
C3b binds to C3 convertase to form C5 convertase
cleaves C5 protein

cleaved products attract phagocytes to site of infection
assembly of membrane attack complex
conformational change
‘fluid-phase’ C3 convertase forms
cleaves multiple C3 proteins into C3a and C3b

50
Q

CMC

A

complement mediated cytotoxicity

51
Q

ADCC

A

antibody attracts to cytotoxic cells via Fc receptors

target cell antigens become bound to lots of antibodies
effector immune cell lyses target cell

52
Q

Complement mediated cytotoxicity

A

antibody binding results in fixation of complement onto target cell

results in membrane attack complex and cell lysis

53
Q

complement system

A

formed by soluble/humoral components of serum

3 activation pathways

54
Q

effects of complement (4)

A

triggers inflammatory response
attracts phagocytes
degrades membranes
stimulates antibody production

55
Q

3 activation pathways

A

lectin
classical
alternative

56
Q

lectin activation pathway of complement

A

recognition and binding of carbohydrates by collectins

e.g. mannose-binding lectin is a collecting that binds to mannose on the surface of a pathogen

C4 and C2 components are cleaved
they bind to form classical C3 convertase on pathogen cell membrane

57
Q

alternative activation of complement

A

occurs directly at microbial cell surfaces
triggered when C3b protein binds to a microbe

conformational change
'fluid-phase' C3 convertase forms
cleaves multiple C3 proteins into C3a and C3b
C5 convertase forms
all pathways follow the same
58
Q

ficolin

A

collectin that binds to N-acetylglucosamine

59
Q

MASP

A

mannose-binding lectin associates serine protease

60
Q

MAC

A

membrane attack complex

terminal complement complex that ruptures wall of pathogen

61
Q

3 types of Fc receptor

A

Fc- gamma
Fc-alpha
Fc- epsilon

cellular basis of immunity (21 decks)

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