Pages 415-425
Jan 18, 2016
Pages 415-425
Soluble proteins secreted by activated B cells or by their plasma-cell 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 antigenclonal selection creates copies of the activated cell
this is called the primary humoral responsemost clones become antibody producing plasma cellsother clones become memory cells
memory cells provide the secondary humoral responsea much faster, effective, and more prolonged response
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Primary response(initial encounterwith antigen)
Secondary response(can be years later)
Activated Bcells
Plasmacells
Secretedantibodymolecules
Secretedantibodymolecules
Plasmacells
Clone of cellsidentical toancestral cells
Proliferationto form a
clone
MemoryB cell
MemoryB cells
AntigenAntigen bindingto a receptor on aspecific B cell(B cells withnon-complementaryreceptors remaininactive)
Subsequentchallengeby sameantigen resultsin more rapidresponse
Primaryresponse
Secondaryresponse
Antigeninjected
Antigeninjected
Rel
ativ
e an
tib
od
y co
nce
ntr
atio
nin
blo
od
pla
sma
Time (weeks)
0 1 2 3 4 5 6
Active immunitywhen B cells encounter antigens and
produce antibodiesacquired naturally from infection or from
vaccines Most vaccines contain dead or weakened
pathogens
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Passive immunity (temporary protection)Antibodies are obtained from an immune
human or animal donor 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 Y-shaped moleculeEach polypeptide
chain has a variable and a constant region Constant regions
determine antibody function and class
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Five major immunoglobulin classes (MADGE):1. IgM—can fix complement2. IgA—found mainly in mucus3. IgD—important in activation of B cell4. IgG—can cross placental barrier; fixes complement5. IgE—involved in allergies
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T lymphocytes are activated indirectly:Antigens must be presented by APCs
This is known as antigen presentationT cell recognizes and binds to the antigen fragmentT 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 Binds, releases lethal chemicals that degrade membrane and
digest proteins Helper T cells
Direct/manage cloning, signal with APCs, release chemicals called cytokines which increase efficiency of response
Regulatory (suppressor) T cells 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) ADAPTIVEIMMUNE RESPONSE
CELLULAR (CELL-MEDIATED) ADAPTIVEIMMUNE RESPONSE
Antigens displayed byinfected cells activate
CytotoxicT cell
Macrophage
Antigen-presentingcell
Antigen (1st exposure)
Engulfed by
Becomes
Stimulates
Stimulates
Free antigensdirectly activate
B cellT cell
Gives rise to Stimulates Stimulates
Plasmacells
Secrete
Antibodies
MemoryB cells
Defend against extracellular pathogens bybinding to antigens and making them easiertargets for phagocytes and complement.
Stimulates
Defend against intracellular pathogens andcancer by binding to and lysing the infectedcells or cancer cells.
Antigen (2nd exposure)
Stimulates
MemoryT cells
StimulatesHelper
Memory
T cell
Gives rise to
ActivecytotoxicT 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 http://highered.mheducation.com/sites/0072507470/student_view0/
chapter22/animation__t-cell_dependent_antigens__quiz_1_.html
Clonal Selection 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/ch23/cell_mediated.swf
Major types of tissue graftsAutografts—tissue transplanted on the
same person most successful
Isografts—tissue from an identical person (twin)
Allografts—tissue from unrelated person most common
Xenografts—tissue from a different animal species (whole organs unsuccessful)
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Blood group and tissue matching is doneensures 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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