Transcript Ch 12 Adaptive Defense Mechanisms

Pages 415-425

Soluble proteins
secreted by activated B
cells or by their plasmacell offspring (in
response to an antigen)

They are capable of
binding specifically with
that antigen

Also known as
immunoglobulins or Igs
B
lymphocyte activation and clonal selection:

First they bind to a specific antigen
clonal selection creates copies of the activated cell




this is called the primary humoral response
most clones become antibody producing plasma cells
other clones become memory cells

memory cells provide the secondary humoral response
 a much faster, effective, and more prolonged response
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Primary response
(initial encounter
with antigen)
Activated B
cells
Proliferation
to form a
clone
Plasma
cells
Antigen
Antigen binding
to a receptor on a
specific B cell
(B cells with
non-complementary
receptors remain
inactive)
Memory
B cell
Secreted
antibody
molecules
Secondary response
(can be years later)
Clone of cells
identical to
ancestral cells
Subsequent
challenge
by same
antigen results
in more rapid
response
Plasma
cells
Secreted
antibody
molecules
Memory
B cells
Relative antibody concentration
in blood plasma
Secondary
response
Primary
response
0
1
2
3
4
5
Time (weeks)
Antigen
injected
Antigen
injected
6
 Active


immunity
when B cells encounter antigens and produce
antibodies
acquired naturally from infection or from
vaccines

Most vaccines contain dead or weakened pathogens
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 Passive

Antibodies are obtained from an immune human
or animal donor



immunity (temporary protection)
Naturally by mother to fetus via placenta; child via
breast milk
Artificially by way of an immune serum containing
antibodies (antivenoms, antitoxins, gamma globulin)
No immunological memory is established
 Four
amino acid
chains linked by
disulfide bonds to
form a T- or Yshaped molecule

Each polypeptide
chain has a variable
and a constant
region

Constant regions
determine antibody
function and class
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 Five
1.
2.
3.
4.
5.
major immunoglobulin classes (MADGE):
IgM—can fix complement
IgA—found mainly in mucus
IgD—important in activation of B cell
IgG—can cross placental barrier; fixes complement
IgE—involved in allergies
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T

lymphocytes are activated indirectly:
Antigens must be presented by APCs

This is known as antigen presentation

T cell recognizes and binds to the antigen fragment
T cell also recognizes and binds to “self” glycoprotein
on APC

Clonal selection occurs

 Clones
differentiate into various T cell classes
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
Cytotoxic (killer) T cells


Helper T cells


Direct/manage cloning, signal with APCs, release chemicals
called cytokines which increase efficiency of response
Regulatory (suppressor) T cells


Binds, releases lethal chemicals that degrade membrane and
digest proteins
Release chemicals that slow down B and T cell activity; cease
the response after removal of antigen
Memory cells


Remember each unique antigen
second response is harder, better, faster, stronger…

that’s where Kanye got that song!!
HUMORAL (ANTIBODY-MEDIATED) ADAPTIVE
IMMUNE RESPONSE
CELLULAR (CELL-MEDIATED) ADAPTIVE
IMMUNE RESPONSE
Antigen (1st exposure)
Engulfed by
Macrophage
Free antigens
directly activate
Antigens displayed by
infected cells activate
Becomes
Antigenpresenting
cell
Stimulates
Helper Stimulates
Stimulates
B cell
Cytotoxic
T cell
T cell
Memory
T cell
Gives rise to
Stimulates
Stimulates
Stimulates
Antigen (2nd exposure)
Stimulates
Gives rise to
Active
cytotoxic
T cells
Plasma
cells
Secrete
Memory
B cells
Memory
T cells
Antibodies
Defend against extracellular pathogens by
binding to antigens and making them easier
targets for phagocytes and complement.
Defend against intracellular pathogens and
cancer by binding to and lysing the infected
cells or cancer cells.


Class II MHC: The main function of major histocompatibility
complex (MHC) class II molecules is to present processed antigens
which are derived from exogenous sources; they are critical for
the initiation of the antigen-specific immune response.
T cell dependent antigens


Clonal Selection


http://highered.mheducation.com/sites/0072507470/student_view0/chapter22/
animation__t-cell_dependent_antigens__quiz_1_.html
http://highered.mheducation.com/olcweb/cgi/pluginpop.cgi?it=swf::600::480::/
sites/dl/free/0073532215/788107/Clonal_Selection.swf::Clonal%20Selection
Cell mediated Immunity

https://smartsite.ucdavis.edu/access/content/user/00002950/bis10v/media/ch2
3/cell_mediated.swf
 Major

Autografts—tissue transplanted on the same
person



most successful
Isografts—tissue from an identical person (twin)
Allografts—tissue from unrelated person


types of tissue grafts
most common
Xenografts—tissue from a different animal
species (whole organs unsuccessful)
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 Blood

group and tissue matching is done
ensures the best match possible
 Cell
membrane antigens must have a 75%
match (or better) to continue with transplant
 immunosuppressive therapy follows
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