t cells Flashcards
the subsets of t cells
t helper cells - prolific producers of cytokines, prolate activity of other immune cells
t cytotoxic cells - directly destroy infected abnormal self cells
t regulatory cells - help control activity of t cells, very important in maintaining immunological tolerance
what are the classifications of t cells
they are classed as being CD4+ or CD*+
all express CD3 (pan t cell marker)
CD4+ - t helper cells (Th)
they secrete cytokines that determine and regulate immune responses
CD8+ - t cytotoxic (Tc)
kill abnormal self cells
what are the CD4+ t cells subsets
TH1
TH2
TH17
TREG
antigen recognition by T cells
ag recognition is via the t cell receptors (tcr)
t cells are MHC restricted
tcr i only recognises protein antigens presented as mhc peptite complexes on host cells
what are the 2 main classes of MHC molecules
MHC class 1 - present antigen peptides o CD8+ t cells
MHC class 2 present antigen tic peptides to cD4+
what is the requirement for antigen processing - major histocompatibility complex
the genes located on chromosome 6 in humans
the mhc genes are highly polymorphic
class 1 molecules expressed on most cells
class 2 molecules expression is only limited to antigen presenting cells mainly dendritic and macrophages
co - receptors ( cd4 and cd8) on t cells recognise specific classes of mhc
what are the two ways antigens are processes
cytosolic pathway - processes endogenous antigens - such as viral protein tumour antigens
peptides generated bind to mhc class 1 molecules and presznet to cd8+ t cells
endocytic pathways - processes exogenous antigens following phagocytosis
peptides generated bind to MHC class 2 molecules and present to cd4+
what is the immunological synapse
signal 1 - tcr?mhc peptides interaction with coreceptor binding
signal 2 - costimulation by a different set of proteins
consequence - signal transduction resulting in gene expression and cytokine release
cytokines produced by t helper cells determine the nature and magnitude of the immune response
what are super antigens
they bind directly to mhc molecules with no processing
they interact with regions of the tcr that result in t cell activation regardless of the specificity of the t cell
results in massive cell activation
