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Infection & Immunity > B and T Cells > Flashcards

B and T Cells Flashcards

1
Q

what are the four stages of adaptive immune response

A

antigen recognition, lymphocyte activation, effector responses, homeostasis

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2
Q

what are T-cell effector responses

A

cell mediated cytotoxicity, activation macrophages, recruitment of neutrophils

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3
Q

what are B-cell effector responses

A

antibody production

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4
Q

what are cytokine effector responses

A

IL-2/4/5/13, IFNgamma, TGFbeta, lymphotoxin, all produced by T-cells
most activate other cells, stimulate antibody production
TGFbeta inhibitory

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5
Q

what is the process of B cell action

A

microbial protein antigen attaches to B cell -> receptor mediated endocytosis of antigen -> antigen processing and presentation -> class 2 MHC-peptide complex attaches to B7 on B cell -> T-cell recognition of antigen

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6
Q

what are B cells

A

mature in the bone marrow and express IgD receptors on surface
antigenic challenge (in lymph node) results in processing and presentation of antigenic fragments to Th cells
Th2 cells provide costimulatory signals required for B cell activation and ab production (CD40L and IL-4)
class switching and somatic hypermutation improve antibody affinity and function
some remain after antigen elimination as memory cells

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7
Q

how are B cells activated

A

by engagement of surface antibodies plus costimulatory signals from T-cells
the signal is enhanced by engagement of complement coreceptor

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8
Q

what is B cell action

A

antigen presentation to T-helper cells, activation of T cell (expression of CD40 ligand, cytokine secretion), activation of B cell by cytokines and CD40 ligation, B cell proliferation and differentiation

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9
Q

what is down regulation of B cell activation

A

signals for B cells are down regulated by engagement of Fc coreceptor

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10
Q

what are antibodies

A

produced by B cells - humoral immunity
20% plasma protein, specific recognition of antigen, target circulating microbes and toxins for phagocytosis, provide active and passive immunity

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11
Q

what are the hypervariable regions

A

regions on antibodies that vary to accommodate antigens

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12
Q

how are antibodies produced

A

during maturation in the bone marrow B cells undergo irriversible genetic recombination to produce an antibody of restricted specificity
membrane bound IgM form, then IgD
antibody generally binds antigen with weak affinity/high avidity
activation of B cell leads to Ig class switching (G, A, E) and somatic hypermutation
activated B cells become plasma cells and some become memory cells

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13
Q

what are Fc mediaed effects

A

mediates many of the effector functions of antibodies; variability in Ig class affects function
IgG binds FcR on neutrophils and mac to promote phagocytosis
IgE Fc causes eosinophil activation and mast cell degranulation
IgG and IgM can trigger complement activation by binding C1q
all require bound antigens to initiate cross linking of antibodies

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14
Q

how are antibodies used as tools

A

can detect proteins in a lab
can detect antibodies in patients
prevent/treat diseases - vaccines, antibody therapies

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15
Q

what are blocking antibodies (ADCC)

A

antibody binds to receptor or ligand to prevent receptor binding and activation (anti TNF)
called antibody dependent cellular cytotoxicity

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16
Q

where are B cells stored

A

lymph nodes

17
Q

what are B cell receptors made of

A

antibodies; recognises, engulfs and breaks up an antigen and keeps the fragment on the surface so it can be recognised by a Tcell

18
Q

where are t cells stored

A

lymph nodes

19
Q

what is somatic hypermutation

A

growing collection of antibodies can cause mutation

20
Q

what is passive immunity

A

e.g. travel vaccinations that provide antibodies but do not stimulate the immune system

21
Q

what is active immunity

A

active intake of pathogen to trigger memory cell formation

22
Q

what are T cells

A

thymus selected lymphocytes, required for cell mediated immunity
removal of intracellular pathogens by killing infeced cells, respond to antigenetic fragments presented by MHC molecules
required to help B cells become activated and produce antibodies

23
Q

what do helper T-cells (CD4+) do

A

recognise antigenic fragments presented on class II MHC

24
Q

what do Th1 cells do

A

activate macrophages and cytotoxic T cells (IFNgamma, TNFalpha)

25
Q

what do Th2 cells do

A

provide costimulatory help to B cells (IL-4, IL-5, IL-10)

26
Q

what regulates T cell differentiation

A

cytokine production

27
Q

what is the role of cytotoxic T cells (CD8+)

A

recognise antigenic fragments presented on class I MHC, kill infected cells

28
Q

what is TCR

A

similar structure and assembly as antibodies
associated with CD3 signalling chains and CD4/8
undergo thymic selection for self tolerance
no somatic hypermutation - ag affinity remains low

29
Q

what is the major histocompatibility complex

A

human leukocyte antigens
two classes; MHC I and MHC II
large number of different alleles, inherit 12 genes with no individual likely o be the same

30
Q

what is MHC class I

A

recognised by CD8+ T cells

31
Q

what is MHC class II

A

recognised by CD4+ T cells

32
Q

what is antigen recognition

A

T cells only recognise a small fragment of antigen
it requires endocytosis, processing and presentation by APC in conjunction with MHC molecule; peptide fragments bind in groove of MHC; TCR binds across both peptide and MHC residues
CD4/8 bind MHC to prevent T cells killing APCs

33
Q

what is positive T cell selection

A

if T cell does not recognise and bind MHC it is signalled to die by apoptosis

34
Q

what is negative T cell selection

A

T cell binds strongly and is activated - signalled to die by apoptosis

35
Q

where are T cells kept alive

A

in peripheral lymphoid organs by continual interaction with self peptide/MHC
they become activated when encountering foreign antigen presented on self MHC

36
Q

what is co-stimulation

peripheral tolerance

A

T cells do not activate in response to an antigen alone, normal T cell activation required a second signal which is generated by co-stimulatory molecules
engagement of TcR signal without co-stimulation causes T cell to become unresponsive and probably undergoes apoptosis

37
Q

what is the inihibitory signal in costimulation

A

CD28 expressed on resting T cells, B7-2 expressedon resting APCs
antigenic engagement of TCR leads to activation of CD28 by binding B7-2
folowed by upregulation of CTLA-4 and B7-1
engagement of these acts as inhibitory signal

38
Q

what are TH1 effector responses

A

migrate to site of infection, release IFNgamma to activate macrophages, simulate production of monocytes in bone marrow, increase expression of adhesion molecules on endothelium, induce leukocyte migration via chemokine release

39
Q

what are the TH2 effector responses

A

provides signal two to B cells

Infection & Immunity (22 decks)

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