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Mechanisms of Microbial Diseases > Adaptive Immune System > Flashcards

Adaptive Immune System Flashcards

1
Q

what are two types of adaptive immunity

A 
Antibody mediated (humoral) immunity 
cell-mediated immunity
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2
Q

what is an antigen

A

old definition ‘antibody generator”
new definition: any molecule that reacts specifically with Ab or Ag receptor on lymphocyte
does not necessarily induce IR

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3
Q

what is an immunogen

A

Ag that can induce IR

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4
Q

Antigenic/ immunogenic

A

relative ability of Ag to elicit IR

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5
Q

Antigenic determinants=

A

epitopes
discrete regions of Ag molecule specifically recognized by adaptive IR
e.g. stretch of 10 or more AA
e.g. 3D structure/protusion in a molecule
antigenic structure

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6
Q

Antibody-mediated (humoral) immunity
what is the main component

produced by

A

antibody is the main component

produced by B-lymphocytes =B cells (develops in Bursa of birds, bone marrow in humans)
neutralizes free-floating particles (bacteria, toxins and viruses)

in response to extracellular Ag, B cells triggered to proliferate and differentiate into plasma cells

Y-shaped proteins called Abs
some B-cells form memory cells that respond faster when exposed to the same antigen again

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7
Q

Antibody structure

A

two functional regions

2 identical arms and 1 stem

Arms- bind to specific antigen (Fab)

Stem -tags antigen for destruction by other IS components (Fc- binds phagocyte)

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8
Q

Light chain

A

two types based on amino acid sequence of the constant regions
λ and k
A given B cell will produce Ab of only one specificity
Both L chains are identical, so either both will be Lλ or Lk

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9
Q

Heavy chain

A 
five types based on AA sequence of the constant region, gives the 'class' of the antibody type 
 µ = IgM
 γ = IgG
 α = IgA
 δ = IgD
 ε = IgE
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10
Q

γ = IgG structure

A 
makes up 75% of serum immunoglobulins 
has basic monomeric structure 
four subclasses based on amino acid sequence of the C regions of the H chains 
IgG1, IgG2, IgG3, IgG4
 IgG1 is most prevalent
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11
Q

γ = IgG functions

A

opsonization -enhances phagocytosis, acts as a flag for phagocytes when Fab is bound to antigen and Fc is freely exposed
neutralizes viruses and toxins
main Ab type made in secondary response, when body encounters Ag for a second and subsequent times
crosses placenta -passive immunity for fetus from mother

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12
Q

µ = IgM structure and functions

A

Monomeric, when attached to B-cell surface as a receptor
it is pentameric in serum, 5 monomers held together by a J chain

First Ab class produced in primary response
Ag receptor on B cells
activates part of innate defenses
agglutinates particulate Ag e.g. bacteria

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13
Q

δ = IgD

A

monomeric form
Found in serum and on B cell surface as receptor
very low amounts, <2% of total serum Ab

unknown function -back-up incase IgG non-functional or not made????

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14
Q

α = IgA

A

primary Ab produced by cells of the mucus membrane
secretory Ab, found in mucosal secretions
Low amount and monomeric form in serum
Dimeric in secretions

Functions:
neutralizes bacteria and viruses by preventing them from attaching to mucus membranes
passive immunity in breast milk

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15
Q

ε = IgE

A

monomeric form, low levels in serum
Ag receptors on Mast cells (tissues) and basophils (blood)
functions: anaphylactic hypersensitivity

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16
Q

how is the classical complement pathway activated?

A

when Ab binds to an Ag -activates C1
converts it to C1qrs: splits C4 and C2 farming C4b2a = C3 convertase (similar to C3bBb in alternative pathway)
remaining events same as alternative pathway
C3 convertase splitting C3 into C3b and C3a (which together with C5a act as anaphylatoxins)
C3b binds to microbe-Ab compex and remaining components join in (C5b, C6, C7, C8, C9) to form MAC attack

17
Q

Role of T-Lymphocytes

activation and summary

A

T-cells, Cell-mediated immunity -mature in thymus
Do not recognize free Ag, rather Ag must be presented by one of body’s own cells e.g. bacterial or virally infected cells, transplant tissues, cancer

Bind to peptide derived from intracellular organisms complexed with Major Histocompatibility Complex (MHC) molecule
T-cell receptor (TCR) binds the complex of MHC molecule and peptide
T-lymphocytes are activated
T-lymphocytes help macrophages kill intracelllular parasites
T helper type 1 (Th1) + Class 2 MHC -> T-cell release macrophages activating factors (IFNγ), NO radicals

18
Q

Two major functional population of T-cells

A

surface markers (cluster of differentiation)

cytotoxic T cells

Helper T cells

19
Q

Cytotoxic T cells

A 
differentiate into Tc which destroy infected or cancerous cells -CD8
recognize Ag presented by MHC class 1 molecules
20
Q

Helper T cells

A

differentiate into Th which activate B cells and macrophages -CD4
Th1 -activate macrophages
Th2 -activate B cells

recognize Ag presented by MHC class 2 molecules

21
Q

difference in structure for MHC 1 and 2

A

MHC class 1 3 alpha subunits and one beta2m

MHC class 2 two alpha and 2 beta

22
Q

Role of T-lymphocytes once activated

A

T-lymphocytes help macrophages kill intracellular parasites
Th1 cells + Class 2 MHC -> T-cell release macrophage activating factors (IFNγ) -no radicals

T-lymphocytes inhibit intracellular replication of viruses 
viral infected cells express class 1 MHC 
recognized by Tc cells
23
Q

what is the lymphoid system

what is it designed to do, what does it contain

A

collection of tissues and organs designed to bring B an d T cells into contact with Ags that enter the body

lymphocytes are highly specific, only recognize 1 or 2 Ags -essential that approriate lymphocyte encounters given Ag to mount effective IR

lymphoid vessels -carry lymph

24
Q

Primary Lymphoid organs

what happens here

A

bone marrow and thymus

hematopoietic stem cells develop into B and T cells

both B and T cells originate in bone marrow but only B cells mature here, T-cells mature in thymus

once matured, lymphocytes gather in secondary lymphoid organs waiting to encounter Ag

25
Q

encapsulated secondary lymphoid organs -> immune response

A

lymph node-> to antigens in tissues

spleen -> to antigens in blood

26
Q

unencapsulated secondary lympoid organs -> immune response

A

MALT -> to antigens at mucosal surfaces

27
Q

secondary lymphoid organs

A

site where lymphocytes gather to collect Ags
e.g. lymph nodes, spleen, tonsils, adenoids, appendix

situated at strategic positions in body to capture Ags
e.g. lymph nodes capture ags from lymph, spleen captures from blood

after lymphocytes make contact with Ag they proliferate forming clones of cells specific for that Ag

some lympoid organs less organized
MALT -prevents invasion from mucosal surface
SALT -prevents microbes invading skin

28
Q

Difference in surface markers

A

CD molecule (cluster of differentiation)

B-cells -surface immunoglobulin

T-cells -T-cell receptors (TCR)

29
Q

Clonal selection and expansion of B-lymphocytes

A

as lymphocytes mature in primary lymphoid tissue, a population of cells generated that are able to recognize limitless variety of Ags

each individual cell is able to recognize and respond to 1 epitope

body is estimated to have 1 billion B cells but only a few recognize a given epitope

30
Q

how does clonal selection and expansion work for B-lymphocytes

what prevents IS from acting against itself

A

Only B cells capable of making corret Ab bind to Ag = “clonal selection”

Cells that bind Ag begin dividing, produce population of clones= “clonal expansion”

somatic mutations for further selection

most lymphocytes require 2nd opinion (accessory signals) from another cell (Th cell) before activation to occur, prevents IR against self

31
Q

clonal selection and expansion of T-lymphocytes

A

similar to B cells
some of these cells release cytokines, others have cytotoxic function
no further selection as a result of somatic mutations
a fraction of clonally expanded population differentiates into memory cells

t memory cells CD45RO
b memroy cells CD27 and surface IgG,A or E

32
Q

memory cells

A

more readily stimulated by antigen
greater combining power

B cells through mutation and selection
T cells, increased expression of accessory adhesion molecules

basis for the principle of vaccinations

33
Q

two types of T-independent antigens

A

polyclonal activators

repeating determinants

don’t need a Th cell to give a second response.

34
Q

cytokines

A

soluble intercellular communication factors

important role in protection against infectious diseases

  • control of infection
  • development of pathology
35
Q

cytokines -> interferons

A

a viral infected cell will produce interferons to bind to an uninfected cell and induce that cell to produce anti-virals

36
Q

cytokine production helps define T-helper subsets by

A

mutual antagonism between two subsets

autoregulation of immune system

Mechanisms of Microbial Diseases (8 decks)

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