BIOL 1104 Lecture Notes - Cytolysis, Cytotoxicity, Apoptosis

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30 Jan 2013
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CD8 CYTOLYTIC T LYMPHOCYTES (CTL)
functions: virally infected cells (MAJOR)
bacterial infected cells
tumor cells
graft rejection
important that their activity is confined only to target cells
some CD4 and some NK cells also have cytolytic activity
PROTECTION AGAINST VIRAL INFECTION
antigenic viral proteins can be cytosolic or nuclear-localized
viral escape mechanisms –
latent infection
privileged site replication (cells lacking MHC I)
inhibit class I MHC expression
inhibit TAP1/2 activity (peptides cannot enter ER)
mutation in antigenic peptide sequence
PROTECTION AGAINST BACTERIAL INFECTION
several types of bacteria can reside and replicate WITHIN host cells
Salmonella, Listeria, Myobacteria
while this might elicit MHCII/CD4 response in some cells, certain cell types
LACK these proteins and the MHCI/CD8 route is the only alternative
ACTIVATION OF CTL –
after activation, clonal expansion and expression of cytokines
also expression of cytolytic proteins (perforin, granzymes)
initial stages are CD4 independent, but CD4 is required eventually
mechanism is unclear but maybe…
CD40/CD40L binding
CD4 effect on APC’s
“Cross Priming” – if APC’s are not directly infected
due to protein fragments that are released from cytolysed infected non-APC’s
fragments are taken up and presented by APC’s on MHCI to CD8+ cells
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