Week 4 - Adaptive immunity Flashcards
What is MHC I?
- Receptor on all nucleated cells which presents peptides from within the cell
- Distinguishes self from non-self
What is MHC II?
-Receptor present on antigen presenting cells only which presents peptides from extracellular microbes which have been phagocytosed
What allows there to be high variety of MHC molecules within one person?
-Co-dominant expression of HLA genes
What is meant by HLA being polymorphic?
-Many alleles of HLA amongst the population allows presentation of different microbes and different susceptibilities in different people
Where is the variable region on an MHC molecule?
-Peptide binding cleft
Do MHC complexes have a narrow or broad specificity?
-Broad -> allows many peptides to be presented by same MHC molecule
What cell specifically recognises MHC I?
-CD8+ T Lymphocytes
What cell specifically recognises MHCII?
-CD4+ T Lymphocyte
What are the three steps of antigen presentation?
- Capture
- Processing
- Presentation
What is specific about the location of APCs within the body?
-They are located in areas which allow them to interact with B and T cells eg mucous membranes, lymphoid organs and in the circulation
How do APCs capture pathogens?
- Phagocytosis
- Macro-pinocytosis of soluble particles
How can APCs recognise so many different pathogens?
-Have a wide range of pathogen recognition receptors both extracellularly for bacteria and intracellularly for pathogens
What do Pathogen recognition receptors recognise?
-Pathogen Associated Molecular Patterns
Which type of adaptive immunity is activated by extracellular pathogens?
-Humoral
Which type of adaptive immunity is activated by intracellular pathogens?
-Cell-dependant
What is meant by humoral immunity?
-The immunity which does not involve cells directly in the defence eg antibodies and complement (although B cells are activated by T cells)
What is meant by cell-dependant immunity?
-Cells are directly involved in the defence against the infection eg cytotoxic T cells and macrophages
Name two clinical problems with MHC
- Organ transplant rejection
- Cross reactivity
Explain why MHC can be problematic in organ transplant rejection?
-HLA mismatch between donor and recipient causes destruction of donor tissue by recipient immune system
What is cross reactivity of MHC?
-A microbe resembles human protein and cannot be distinguished eg strep pyogenes innoculates heart valve -> immune system cannot tell self from non-self and begins attacking own tissue ->rheumatic heart disease
Describe antigen presentation to CD4+ cells and the response
- Extracellular microbe phagocytosed and presented on MHC ii by APC
- CD4+ cell binds to MHC ii and recognises non-self peptide
- CD4+ cell activates B cell for clonal expansion and proliferation causing antibody production
Describe antigen presentation to CD8+ cells and its response
- Intracellular microbe displayed on MHC I and MHCii if APC
- Activated CD8+ cell binds to MHC I on infected cell and recognises as non-self and causes cell lysis through perforins and granzymes to kill the cell
- APCs with peptide displayed MHC i can activate CD8+ and also displaying peptide on MHC ii activates CD4+ cells which then activates CD8+ cells
Where do T lymphocytes mature?
-Thymus
What cytokines released by CD4+ induce macrophages?
- IL-1
- IFN-g
