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MBB 231 > lec 15- the immune response part 2 > Flashcards

lec 15- the immune response part 2 Flashcards

1
Q

what do antibodies do?

A
  1. bind to and neutralize a bacterial toxin
  2. coat the pathogen which promotes phagocytosis
  3. activate complement

overall: target pathogens and eliminate them via phagocytosis

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2
Q

what is the secreted form of B-cell receptors?

A

antibodies

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3
Q

what is the structure of an antibody?

A

-2 identical light chains
-2 identical heavy chains
-each light chain is joined to a heavy chain by a disulfide bond
- both light and heavy chains consist of one variable and one constant region (light have one domain, heavy has 3 or 4)

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4
Q

what is the Fab fragment?

A

-fragment antigen binding
-composed of the light chain and part of the heavy chain

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5
Q

what is the Fc fragment?

A

-fragment crystalizable
-a portion of the constant region of the heavy chain

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6
Q

what do the Fab and Fc fragments bind to?

A

Fab binds to the antigen and Fc binds to Fc receptors on cells

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7
Q

what is an epitope?

A

the portion of an antigenic molecule that is bound by an antibody

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8
Q

can an antigen have multiple epitopes?

A

yes,

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9
Q

what does a B-cell do when it recognizes its antigen?

A

it will multiply and produce clones of itself, all of which will secrete antibodies

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10
Q

do B-cells tend to recognize inner epitopes?

A

no, they recognize external epitopes

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11
Q

what are the hypervariable regions of an antibody also known as?

A

complementary-determining regions (CDRs)

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12
Q

what do the 6 hypervariable regions of heavy and light chains form?

A

antigen binding sites

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13
Q

what are the three steps of the generation of B cell antigen recognition diversity?

A
  1. somatic recombination
  2. junctional diversity
  3. combinatorial diversity
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14
Q

what is somatic recombination?

A

-to generate variable region of light chains, V and J segments are joined
-to generate variable region of heavy chains, one V, D, and J segments are joined
- V, D, and J segments are randomly chosen from many

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15
Q

what is junctional diversity?

A

addition of new and random nucleotides at the V and J segments of light chain and D and J segments of heavy chain

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16
Q

what do the randomly chosen V gene segments code?

A

they code CDR1 and CDR2

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17
Q

what does junctional diversity code?

A

CDR3

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18
Q

what is combinatorial diversity?

A

-B cells with intact heavy chains undergo clonal expansion, light chain generation then takes place (same heavy chains but light chains can be different)
-different light chains combine the already generated heavy chains
-before B cells leave bone marrow, they undergo a selection so they dont recognize themselves

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19
Q

A clone of mature B cells released from bone marrow have:

A

one antigen specificity and express lgM receptors, meaning first class of antibodies are lgM class antibodies

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20
Q

what happens when B cells leave the bone marrow?

A

-they circulate between blood and lymph, need antigen to be activated
-need help of T cells to secrete antibodies
-takes place in lymph node
-B cells will phagocytose the antigen and preset pieces of it to helper T cells

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21
Q

what are class I MHC molecules?

A

molecules that are expressed on all nucleated cells, generally present viruses to cytotoxic T cells (CD8) which kills infected cell

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22
Q

what are class II MHC molecules?

A

molecules that are expressed on professional antigen presenting cells, present extracellular pathogens that must be phagocytosed before presentation

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23
Q

what is the structural difference between class I and II MHC molecules?

A

class I: one transmembrane alpha chain of three domains that are non-covalently complexed to B2 microglobulin
class II: two transmembrane chains- alpha and beta

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24
Q

what ends up in the binding sites of class I and class II MHC molecules?

A

pieces of antigens

25
Q

when does the T cell receptor recognize antigens?

A

when they are being presented by an MHC molecule that the T cell also recognizes

26
Q

what T cells recognize class I MHC and class II MHC?

A

class I: CD8 cytotoxic T cells receptors
class II: CD4 helper T cells receptors

27
Q

what are the three types of T cells and what do they do?

A

cytotoxic T cells (CD8)- kill infected cells
helper T cells (CD4)- regulate other white blood cell activites and activates macrophages
regulatory T cells- supress activity of other lymphocytes, and help control immune responses

28
Q

what does MHC stand for?

A

major histocompatibility complex

29
Q

what encodes MHC proteins?

A

-stable germline genes from 3 families that encode:
class I heavy chain isotypes
class II alpha chains isotypes
class II beta chains isotypes

30
Q

what is the most polymorphic gene system in the body?

A

MHC

31
Q

how many allotypes of MHC class I do humans have?

A

12, 6 from mom and 6 from dad

32
Q

does each MHC molecule display a range of peptides?

A

yes multiple peptides can fit in the binding sites

33
Q

how do T cells function?

A

T cells function by making contact with other cells, the T cell receptor recognizes antigen attached to MHCs and induce changes in the cell

34
Q

do T cell precursors from the bone marrow express CD8 and CD4?

A

no, they only express it once in the thymus

35
Q

what happens to T cells in lymph nodes?

A

T cells are always activated in a lymph node by dendritic cells first and then go on to perform their effector functions

36
Q

what happens to T cells after activation by dendritic cells?

A

helper T cells stay in lymph node and help cells make antibodies, cytotoxic T cells leave lymph node and kill infected cells

37
Q

what happens to a T cell if they do not encounter an antigen on a dendritic cell to scan?

A

they continue to circulate between blood and lymph, then they die/apoptosis occurs if they never find an antigen

38
Q

what does ITAMS stand for?

A

immunoreceptor tyrosine based activtion motifs

39
Q

what are the 3 signal transduction pathway steps for T cells?

A
  1. T cells ITAMS are not phosphorylated
  2. binding of MHC to T cell receptor leads to ITAMS phosphorylation by Lck
  3. ZAP-70 binds phosphorylated chain ITAMS and is phosphorylated by Lck
40
Q

what is Lck?

A

-Lck (lymphocyte specific protein kinase) a tyrosine kinase

41
Q

where are B cells?

A

circulating between blood and lymph, and encounter antigen in lymph node

42
Q

what is linked recognition?

A

B cells and T cells recognize the same antigen but different epitopes

43
Q

what causes a cognate pair?

A

linked recognition

44
Q

what do B cells in cognate pairs sometimes turn into?

A

lgM secreting plasmoblasts

45
Q

what is a plasmoblast?

A

immature blood cells that secrete antibodies while still dividing

46
Q

why do B cells secrete lgM and where do they exit?

A

to generate antibodies, usually low affinity so they exit blood stream through lymphs and form a germinal center

47
Q

where does somatic hypermutation occur?

A

at the germinal center

48
Q

what is somatic hypermutation?

A

the process a B cell undergoes when it enters the germinal center

49
Q

what does somatic hypermutation do?

A

generates antibodies of higher affinity for the antigen

50
Q

what is affinity maturation?

A

the process B cells undergo if they display a higher affinity

51
Q

what does affinity maturation do?

A

makes a B cell with high affinity undergo class/isotype switching again with the aid of a helper T cell

52
Q

what do B cells become after affinity maturation?

A

either plasma cells or memory cells

53
Q

what drives the single nucleotide substitutions in centroblasts?

A

activation-induced cytidine deaminase (AID), made by B cells

54
Q

what determines if B cell becomes plama cell or memory cell?

A

-helper T cells (specifically Tfh cells)
-need for antibodies makes plasma cells
-when an infection subsides, the same cytokines direct formation of memory cells

55
Q

where are long lived and short lived plasma cells?

A

long lived = bone marrow
short lived = lymph node

56
Q

what are long lived antibodies that are in bone marrow and ready to circulate and act called?

A

serological memory

57
Q

what activates long lived memory B and T cells?

A

if the pathogen establishes re-infection

58
Q

how does CD8 T cells kill infected cells?

A

-only one infected: recognize the infected cell then programs it to die, while neighbouring cells are fine

-multiple infected cells: recognized infected cell then programs it to die, then goes to second then third. First is dead, second is dying, third is being attacked

MBB 231 (17 decks)

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