Antigen presenting cell Flashcards
What are APCs
Heterogeneous group of immune cells that mediate the cellular immune response
Process and present antigens for recognition by certain lymphocytes
What are professional APCs
Macrophages, B cells and dendritic cells that present foreign antigen to helper t cell
Where does the peptides originate from in class I and II MHC molecules
Endogenous or intracellular for MHC class I Exogenous or extracellular for MHC class II
What is B7 protein
Membrane protein found on activated APCs
Produce co-stimulatory signal co-inhibitory signal to enhance or decrease the activity of MHC-TCR signal
Binding of B7 of the APC to CTLA-R of T cells causes inhibition of the activity of T cells
What does B7 pair to
Pairs with either a CD28 OR CD152 (CTLA-4) surface protein of t cell
What differentiates dendritic cell from other professional APCs
Constitutively express high levels of MHC II and the co-stimulatory protein B7
most effective APC
Antigen uptake - endocytosis phagocytosis (by langerhans cells)
What differentiates B cell from other APCs
Constitutively expresses class II MHC but requires activation to produce B7 Antigen uptake - receptor-mediated endocytosis
When do macrophages express class II MHC and B7
After activation via the process of phagocytosis
How are MHC class I antigens presented
Processed in cytosol or in secretory vesicles and presented on class I MHC molecules to CD8+ T cells
How are MHC class II antigens presented
Processed in endoscopes and presented on class I MHC molecules to CD4+ T cells
What signal leads to production of millions of T cells that recognise the antigen
Binding of CD28 of the T cell to CD80 or CD86, initiating T cell proliferation
How is the rapid division on T cell controlled
Stimulation of CD28 induces production of CTLA-4
This competes with CD28 reducing activation signals to T cell and winds down immune response
What is protein tyrosine phosphorylation
Requires CD4/8 interaction
CD4/8 expresses Lck, which is a protein tyrosine kinase (PTK)
PTKs can phosphorylate ITAMs (immunoreceptor tyrosine activation motif)
ITAMs are found within TCR complex
Lck also recruits Zap-70 and phosphorylates it
What helps regulate the response
Tregs Inhibitory cytokines Reverse signalling CTLA-4 helps to downregulate response Suppressing response is necessary
