8.1 Adaptive immunity Flashcards
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.
How do lymphocytes and lymph return to blood from the site of infection?
Via the thoracic duct
Summarise T cells and their functions.
5 types:
- CD8+ (cytotoxic) = kill virus infected cells
- CD4TH1 = activate infected macrophages, provide help to B cells for antibody production
- CD4TH2 = provide help to B cells for antibody production, especially switching to IgE
- CD4TH17 = enhance neutrophil response
- CD4 regulatory T cells = suppress T-cell responses
Summarise B cells and their functions.
- Produce antibodies
- IgM, IgD, IgG, IgE, IgA
- The constant region of the heavy chain is the one that changes between isotypes
- IgM is the first antibody produces by B cells
- IgM is good for activating complement but offers poor tissue penetration, isotype will change to a different type of immunoglobulin depending on what traits are desired
Which 2 antibodies are most prevalent in the oral cavity?
- IgA present in saliva
- IgG in gingival crevicular fluid
How does antibody quality change during the course of an adaptive immune response?
- IgM is the first antibody produced
- Somatic hypermutation takes place (point mutations introduced into variable segments to increase affinity of antibody for antigen)
- Class switching occurs (switching antibody isotype) to IgG which means IgG can act as an opsonin and enhance phagocytosis
Each antibody has different specialised functions, what are some of these?
How does vaccination work?
- Vaccines expose an individual to an attenuated form of a virus, or a safe component of a pathogen
- Body produces T and B memory cells which survive in lymph nodes or peripheral tissues
