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***Midterm on March 8th, but will not include the material taught on March 1st.
David Vetter
Brought attention to adaptive immune system, emphasized its importance
Illustrate how important adaptive immune system is, without v. vulnerable to
Innate immunity
First response to foreign antigen
A stopgap to stop host from dying outright
BUT drawback: v. limited scope of antigen recognition
How recognizes dangerous molecules, pathogens BUT do not recognize those
molecules specifically
oNO memory
oWill respond in same way may be an over response
oDifficult to manage
oNOT A replacement to adaptive immunity
Two types of lymphocytes
T and B cells
Edward Jenner invented coincept of vaccine mounting adaptive immune
response to pathogen
oSo reexposure lifelong protective immunity memory
All organisms have some form of innate immunity
Including plants
Only a small number of organisms have adaptive immunity
oLate event in evolution acquiring adaptive immunity
Right side of cells of immune system
Derive from myeloid progenitor
oCells of innate immune system
Left Hand side lymphoid stem cell
oFocus of todays lecture
Stem cells entire immune system populated by stem cells
oStem cells will give rise to all cells of immune system
T v. B cells
T lymphocyte secretes products
oCell ejecting molecules out of its intracellular compartments
oEjected OUT Of cell

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oNot on surface
oMostly make cytokines give info to immune system
Dictate the type of immune response
Type of cytokines determine response (allergic or killing or
something else)
oKill an infected target
B cells
oSecrete antibodies can directly neutralize pathogens or toxins
Antibodies can also bind or stick to pathogens directly
Titers looking for antibodies in serum that were mounted by the vaccine
Ex. MMR vaccine took or not?
T and B cells have specific receptors stuck to cell surface
How to differentiate from other cells
Receptor integrates into membrane and sticks out in extracellular
Receptor sees outside the cell
T cell has T cell receptor; B has B cell receotr
If T or B cells receptors engaged by something foreign, products secreted
otherwise none will be secreted
1. See something foreign before the T or B cell is activated
B cell secreted product (antibodies) are copies of the BC receptors modified so it
doesnt stick to the cell
oExact same molecule
oAntibody molecules will bind to foreign pathogen
T cell receptor different
oT cell makes cytokines, not more of its receptors
oB cell receptors cleaved off to make antibody molecules secreting the
same receptor molecule in the form of antibody that circulate in plasma
oAntigen immune system responds to
Look foreign to the body
All pathogens decorated with different surface proteins that immune system
recognizes as foreign
oConcludes its an infection
Parts of bacteriawell suited to recognition by T and B cells
oDefined as antigens
oOversimplification because immune system can see other antigens, also
toxins secreted by say diphtheria, self-antigens (in autoimmune patients)
Combination of genetic and environmental influences
oAs long as immune system interpret them as dangerous, foreign
Tumours own cells growing uncontrollably

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oHave own antigens that can trigger immune response
oImmune system also surveying body for possible tumours
oNot well matched organ
oReject new organ
oTransplanted tissue seen as antigen by the immune system
B cells and T cells see antigens VERY DIFFERENTLY
EX. influenza
oB cell will only see antigens on the surface of pathogen
oH1N1 proteins on surface that mutate
Pathogens change, so we change to adapt to that
Need to get continuously vaccinated
oT cells can see proteins buried inside the virus
T cell immunity not gotten by vaccination
V. important because whats inside virus is what keeping it
alive, so its less subject to mutation
B cells see antigens
Antibody molecule has two places to see antigen at the tips of the Y
oThese binding sites are identical
oThe two arms are identical made by same genes
T cells see antigens
Differently from B cells
EX. influenza is a virus
oMost viruses infect cells
By getting inside the cell
Viruses can be carried in body whole life without any issues,
unless immune-compromised
BUT viruses like influenza infect cells we need, like the cells
of the upper respiratory tract
oVirus gets broken up into bits
Cell takes these bits into E reticulum, puts them on the
antigen presenting molecule (MHC)
MHC allows for proteins to get loaded on it
Viral proteins need to be in context of MHC for the immune
system to see it
Now the cell is an antigen presenting cell
NOW T cells recognize the presence of virus
T cells cannot see the bits on their own, these tiny bits need
to be presented with MHC
T cells do not make different antibodies
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