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15 Feb 2011
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LECTURE Feb. 15/2011
T-Cells
Midterm approximately 2 hours, all Multiple choice questions
Results will be posted before drop date
March 1st material not covered on midterm
T-cell triggered by antigen how?
Adaptive immunity requires recognition of antigen; takes longer to develop, days to weeks;
Can recognize 10 billion antigen specificities due to random rearrangement
process in bone marrow at DVJ locus
Highly variable immune system can recognize just about anything and
everything
Can improve as the response progresses
TWO major subsets of lymphocytes B and T
oB secrete antibodies which have same specificity as B cell receptor
displayed on surface of B cell
oT lymphocytes expand and become effector T cells
Debate whether humoral or cellular immunity is more important
Cellular response T cell response helped by dendritic cells
Naïve recipient someone who has never seen the infection before
Ex. response to TB cannot transfer TB immunity with only serum
Innate immune response does not work by clonal selection dumb immunity
everybody responses and responses the same way but adaptive is more selective
Adaptive immune responses
Specific
Diversity
Memory
Self/non-self discrimination
oAutoimmunity when own cells attacked by adaptive immune system
Know when to wind down do not want it to be on all the time
KNOW THESE HALLMARKS
Antigens
Displayed by pathogens
Recognized by adaptive immune system
Other potential antigens include self antigens, tumour antigens, transplanted
tissue
See portion of bacteria, called epitope
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Ex. have TB, will have antibodies to different antigens on different parts of TB
This is the polyclonal response
Polio virus
Three different proteins on the coat
Epitopes are what are seen
Proteins are made only small percentage of genome codes for proteins
Linear epitope runs length of linear protein (before folding)
Conformational epitope seen once the protein is folded
B-cells typically see conformational epitopes
T-cells see antigens differently, CAN see linear epitopes
oBut proteins dont exist in linear form
Influenza mutates year to year
Most mutated proteins are the ones on the surface of the virus particle
T-cell receptors recognize receptors within the coat, those epitopes more
conserved because they typically are crucial for viral replication, etc.
Not foolproof but less susceptible to drift than B-cell epitoptes
Denatured proteins recognized by T-cell receptors
oPeptide antigens recognized
oPeptides are fragments of amino acids
oPeptides made inside infected cell, loaded onto MHC
Cell infected by virus
Peptide must be seen in context of MHC so can respond to pathogen
T-cell expands and makes daughter cells
Summary
T-cells activated by only protein antigens and recgonize peptides only
T-cells recognize only linear peptides
Only one unique t-cell receptor
oSeveral copies of this receptor displayed on surface of cell
PART 2: How T-cell receptor is diverse enough to see so many diff antigens
RANDOM process takes place in bone marrow
Genes code for t-cell receptor locus of genes called T-cell locus receptor
Alpha locus DJ; beta locus VDJ
VDJ recombination
T-cell receptor
Diversity of which VDJ genes selected and put together
More diversity from putting together the alpha and beta chains
T-cell receptor never secreted, stay on t-cell surface always
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