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B4W2 > B AND T CELL MEDIATED IMMUNITY > Flashcards

B AND T CELL MEDIATED IMMUNITY Flashcards

1
Q

describe B cell development in the bone marrow from stem cells

A

stem cells… pro-b cells, pre-b cells… B cells

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2
Q

if B cells come into contact with antigens, what happens?

A

they can activate, proliferate and differentiate into memory cells and plasma cells

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3
Q

what do plasma cells do?

A

produce soluble antibodies and become long-term residents of the bone marrow

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4
Q

what are immunoglobulins

A

antibodies

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5
Q

what are the functions of antibodies?

A

recognise specific molecules, directly kill microbes, directly neutralise toxins, target phagocytes to microbes by opsonisation, regulate immune response, clear foreign antigens, involved in immunopathology and terminate the immune response

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6
Q

what are the 5 classes of antibody?

A

IgA, IgD, IgE, IgG, IgM

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7
Q

what makes these classes of antibodies different?

A

they all have different valencies (number of antibody binding sites) and different functions

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8
Q

what are the subclasses of IgG?

A

IgG1 IgG2 IgG3 IgG4

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9
Q

what is the valency of IgG?

A

2

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10
Q

what are the subclasses of IgA?

A

IgA1 and IgA2

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11
Q

describe the structure of an IgG?

A

made up of 4 polypeptide chains; 2 heavy chains and 2 light smaller chains. in each chain we have different domains. the terminal region is the antigen-binding site which recognises the epitopes.there is a hinge so the antibody is flexible.

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12
Q

what is an epitope?

A

a small number of amino acids on the antigen that is recognised by the antibody

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13
Q

why can different antibodies recognise different antigens?

A

the amino acids at the antigen binding site can change

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14
Q

what is affinity?

A

the strength of the binding action between 1 portion of an antibody and 1 antigen

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15
Q

what is avidity?

A

the overall strength of binding between the whole antibody and all antigens antigen

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16
Q

what is the variable region of the antibody? what is the constant region?

A 
variable= terminal domain of the light and heavy chains
constant= rest of antibody
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17
Q

what is the function of the constant region of an antibody?

A

to determine how a specific antibody will contribute to an immune response

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18
Q

why is it important that antibodies have a hinge?

A

so it can move/rotate/change shape

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19
Q

what is Fab?

A

Fragment Antigen Binding. the region on antibodies that binds to antigens

20
Q

What is Fc?

A

Fragment Crystallizable region. the region of antibody that interacts with the cell surface receptors

21
Q

what is somatic recombination?

A

it is how a progenitor lymphoid cell gains a specific antibody on its surface.

22
Q

what happens in somatic recombination?

A

the gene is pulled together, a loop of DNA is excised and the strand of DNA is glued back together

23
Q

why do antibodies have a fixed specificity for life?

A

as recombination only occurs once in the life of B cells

24
Q

what is clonal selection?

A

a B cell expresses receptors specific to the distinct antigen, determined before the antibody ever encounters the antigen. Binding of Antigen to a cell activates the cell, causing a proliferation of clone daughter cells.

25
Q

why don’t we normally see antibody responses until 2-4 days after an immune response?

A

due to the time taken for clonal selection and cell proliferation to occur

26
Q

what is somatic hypermutation?

A

as cells begin to respond to antigens and proliferate, adjustment of affinity of the antibody can occur.

27
Q

how do somatic hypermutations occur?

A

random mutations are introduced (driven by AID). the body selects the mutants that have a higher affinity and these can then proliferate

28
Q

where do somatic hypermutations occur?

A

in the germinal centres of lymphoid tissue where B cells are proliferating vigorously.

29
Q

What is isotype switching?

A

After immunization or infection, activated B cells can switch antibody isotope that they are expressing to change the effector function of the antibody, and improves its ability to eliminate the pathogen that induced the response

30
Q

what stimulates isotype switching?

A

cytokines

31
Q

what is the valence of IgM? How does this help them with their function?

A
  1. they are the largest antibody so can pick up large amounts of infection to mark for recognition by phagocytes. it protects surfaces in the systemic circulation
32
Q

describe the structure of IgA?

A

it has a valency of 4 but has an accessory protein (secretory piece)

33
Q

what is the function of IgA? how does it structure help?

A

it protects mucosal surfaces as its accessory protein allows it to cross epithelial barriers and enter mucosal sites

34
Q

What is the function of IgE?

A

to protect barrier surfaces and tissue surfaces

35
Q

describe the types of immunoglobulins we have from foetus to adult life

A

IgG is he only antibody that is transferred across the placenta. after birth we begin to develop more IgG and then IgM and then IgA.

36
Q

what do follicular dendritic cells do?

A

They present antigens to potential memory cells, of which only B cells with high affinity B cell receptors can bind.

37
Q

describe T cell dependant activation of B cells?

A

Antibodies recognise and process antigens and display them on their surfaces as MHC class II. T helper cells start producing and expressing IL-4 and CD40 receptors. Meanwhile, elsewhere, helper T cells recognise antigens and are activated and so T cell receptors. B and T cells come into close proximity, so T helper cells bind to the MHC complex as they recognise the antigen. Now T cells bind to antibodies using their CD40 ligand. T cells release IL-4 and these bind to Il-4 receptors on B cells and this is their signal to proliferate.

38
Q

describe T cell formation from stem cells?

A

In the thymus T cell progenitors give rise to thermocytes which ll have different T cell receptors. A positive and negative selection will occur and 98% of T cells will die with the rest entering circulation

39
Q

Describe the T cell receptor structure

A

2 polypeptide chains (alpha and beta- both similar molecular weight), a valency of 1. a transmembrane region

40
Q

What do B cells use antibodies to recognise?

A

conformational epitopes- they look at the tertiary structure and recognise shape

41
Q

what do T cells recognise?

A

linear epitopes. these are small sequences in linear arrangement

42
Q

how do linear epitopes form?

A

antigen processing- phagosomes kill microorganisms and liberate fractions of molecules that can be bound and recognised by a T cell receptor

43
Q

what are major histocompatibility complexes?

A

peptide shuttling proteins that transport peptides to surfaces of cells so they can be recognised by T cells

44
Q

what is the structure of a class 1 MHC?

A

a single heavy chain, made up of 3 domains, bound to an accessory protein called beta 2 micro globulin

45
Q

what is the structure of class 2 MHC?

A

2 polypeptide chains each with 2 domains

46
Q

what are the differences between class 1 and 2 MHC molecules other than structure?

A 
class 1 are expressed on all nucleated cells, present peptides to CD8+ T cells and surveil for virus infections
class 2 are expressed on special antigen presenting cells, present peptides to CD4+ T cells and surveil for exogenous pathogens

B4W2 (11 decks)

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