8.1 Adaptive immunity Flashcards
(31 cards)
Describe adaptive immunity.
- Specific
- Slow response
- Requires exposure to pathogen
- Memory, response improves upon subsequent exposure
- Includes lymphocytes, antigen-recognition molecules (B and T cell receptors), antibodies
What are the genetic differences between adaptive and innate immunity?
- Receptors involved in innate immunity are germline encoded
- Receptors in adaptive immunity are somatically arranged receptors
Give 6 features of adaptive immunity.
- Specificity
- Diversity
- Tolerance: chance of autoimmune attack
- Circulation: lymphocytes specific to a pathogen will travel through the circulation
- Division of labour: not all lymphocytes work equal amounts, they each have their own role
- Memory
The immune system protects against 4 classes of pathogens, what are these?
- Extracellular bacteria, parasites, fungi
- Intracellular bacteria, parasites
- Viruses (intracellular)
- Parastitic worms (extracellular)
What does colonal selection refer to?
The process by which the body produces B and T cells to respond to infections.
Describes how diversity, specificity and tolerance are generated.
What form is the T-cell receptor found in?
Found in membrane bound form.
What form is the B-cell receptor found in?
Found in membrane bound form or in a secreted form.
What are the 2 domains of a T- and B-cell receptor?
They each have a variable domain and constant domain.
Describe the variable domain of T- and B- cell receptors.
- The variable domain/region is involved in recognising the antigen
- Within the variable domain there are hypervariable regions involved in recognising pathofens
What are the 3 mechanisms by which antibodies counter extracellular infection?
- Neutralisation of bacterial toxins
- Opsonisation of bacteria found in the extracellular space
- Complement activation of bacteria found in plasma
What is an epitope?
Epitope = the region of an anitgen recognised by a B/T cell
How do T cell epitopes differ from B cells?
T cell epitopes can be internal and external.
B cells only have cell surface epitopes.
What does MHC stand for?
Major histocompatibility complex
What are the 2 classes of MHC molecules?
- MHC class I: recognised by CD8 positive cytotoxic T cells
- MHC class II: recognised by CD4 positive T helper cells
Describe MHC class I receptors in the process of destroying viruses.
- Virus enters cell and expresses antigens in the cytosol of the cell
- Viral proteins broken down into peptides
- Peptides pass into the ER, MHC class I receptors bind to peptides
- Complex of MHC and viral peptide move to cell surface
- Cytotoxic T cell (CD8 positive) recognises complex and kills infected cell
Describe MHC class II receptors in the process of destroying extracellular bacteria, parasites and fungi in macrophages.
- Macrophage engulfs and degrades bacterium, producing peptides
- Bacterial peptides bound by MHC class II in vesicles
- Bound peptides are transported by MHC class II to the cell surface
- T-helper cell (CD4 positive) recognises complex and activates macrophage
Describe MHC class II receptors in the process of destroying extracellular bacteria, parasites and fungi in B cells.
- Cell-surface immunoglobulin of B cell binds bacteria and engulfs into cell
- Degrades bacteria to produce bacterial peptides
- Peptides bind to MHC class II proteins in endocytic vesicles and transported to cell surface
- T-helper cell recognises complex and activates the B cell to produce antibodies
How is BCR and TCR diversity generated?
B and T cell receptor diversity.
2 mechanisms:
- Combinatorial diversity: different combinations of varibale gene segments
- Junctional diversity: loss or gain of nucleotides at junctions
What is the risk that comes with the way BCR and TCR diversity is generated?
Because different gene segments are brought together in a random fashion, it is possible for us to produce antibodies against our own antigens- risk of autoimmune disease.
Where do antigen specific T cells encounter antigen presenting cells?
In the lymph nodes and secondary lymphoid tissue (spleen).
Describe the dendritic cell.
- Professional antigen presenting cell
- Many dendrites making them efficient at phagocytosis and pinocytosis
- Have large numbers of toll like receptors (activation of these enhances processing of pathogen-derived antigens)
Describe the action of dendritic cells when they encounter a pathogen.
- Immature dendritic cells encounter pathogens and are activated by PAMPs
- TLR signaling induces the CCR7 receptor and enhances processing of pathogen-derived antigens
- CCR7 directs migration into lymphoid tissues and augments expression of co-stimulatory molecules and MHC molecules
What are the 3 routes of antigen processing and presentation by dendritic cells?
What is a key function of mature dendritic cells?
Mature dendritic cells are extremely efficient at stimulating naive T cells.
Known as priming.
