Session 3: Adaptive Immune Response: Recognition Phase Flashcards
What are Naive T cells?
They are inactivated T-cells the needs to be presented by antigen presenting cells.
Give some features of antigen presenting cells.
They have a strategic location. They can capture pathogens There’s a diversity in pathogen sensors called Pathogen Recognition Receptor
What are the strategic locations of antigen presenting cells?
• Mucosa associated lymphoid tissue (MALT): Skin (SALT Mucous membranes (GALT, NALT, BALT, GUALT) Tonsils or Peyer’s patches • Lymphoid organs (Lymph nodes, spleen) • Blood circulation
How do antigen presenting cells capture pathogens?
Phagocytosis Macropinocytosis
What are the different pathogen recognition receptors (PRRs)? (Two main groups)
Extracellular pathogens (bacteria) Intracellular pathogens (viruses) Most are toll-like receptors and some NOD receptors.
What are the sensors of Adenovirus?
TLR9
Where are the sensors of Staphylococcus aureus?
TL2/4/9
Give examples of different types of antigen-presenting cells.
Dendritic cells Langerhans cells Macrophages B cells (BCR)
Location and presentation to of: Dendritic cells.
Lymph nodes, mucous membranes and blood. Present to Naive T cells
Location and presentation to of: Langerhans cells
Skin Naive T cells
Location and presentation to of: Macrophages
Various tissues throughout the body. They present to effect T cells which will produce cytokines to attract more macrophages for enhanced phagocytosis. Effector T cells are already activated.
Location and presentation to of: B cells (BCR)
Lymphoid tissue. Present to both effector T cells and Naive T cells
Role of MHC (Major Histocompatibility complex).
To present peptides from pathogens to CD4+ T cells or CD8+ T cell.
On which cells can you find MHC class I molecules?
They are expressed on all nucleated cells.
On which cells can you find MHC class II molecules?
They are expressed on dendritic cells, macrophages and B cells.
So which MHCs can you find on macrophages?
Both MHC class I and MHC class II because macrophages are nucleated.
Give the key features of MHC class I and class II molecules.
They have co-dominant expression so the number of different MHC molecules is high. They have polymorphic genes with different alleles so the number of microbial antigens being presented will be high as well.
Functions of antigen-presenting cells.
They process microbes via exogenous pathways or endogenous pathways. They present microbial peptides to T cells.
Explain the endogenous pathway of processing of intracellular microbes.
There is a microbial protein present in the cytoplasm. In the form of a virus or tumour antigen.
It is then marked for destruction by proteasome.
A proteasome-generated peptide is then transported to ER by TAP proteins.
There is then a formation of peptide-MHC class I complex if there is a right match.
The peptide is then presented to CD8+ T cells.
Explain the exogenous pathway of processing intracellular microbes.
The microbe is captured by phagocytosis or micropinocytosis.
Degradation into small peptides in endosomes.
Peptide-rich vesicles fuse with vescile containing MHC-class II molecules.
Formation of peptide-MHC class II complex if right match.
This only occurs in antigen presenting cells including dendritic cells, B cells and macrophages.
The peptide is then present to CD4+ T cells.
What T cell recognises MHC class I?
CD8+ T cells
What T cells recognises MHC class II?
CD4+ T cells
What type of pathogen is common for the exogenous pathway?
What type of immunity is common?
Bacteria
Humoral immunity (antibodies, complement and phagocytosis)
What type of pathogen is common for the endogenous pathway?
What type of immune response is common?
Viruses
Cell-dependent immunity (Cytotoxic T lymphocytes, antibodies and macrophages)
What is the clinical importance of MHC molecules?
Host can deal with a variety of microbes
No two individuals have the same set of MHC molecules
Different susceptibility to infections
Why might some HIV-infected individuals progress slower than others?
Depending on their set of MHC molecules.
There are slow progressors and rapid progressors.
Depending on what MHC molecules they have they will fall ill quicker than others.
Slow progressors will show an effective T cell response against infected cells because their MHCs can recognise key peptides for the survival of the virus.
Rapid progressors will show a poor T cell response because of poor recognition of infected cells. This is because their MHCs may only recognise less critical peptides for the survival of the virus.
What are some clinical problems with MHC molecules?
It’s a major cause of why organs might be rejected by the new host in an organ transplant. If the HLA molecules mismatch the new host might not accept it.
HLA molecuels are associated with autoimmune disease like ankylosing spondylitis and insulin-dependent diabetes mellitus.
Case of cellulitis.
Give causative organism.
Antigen presenting cells
Sensor
Mode of capture and pathway of processing antigen.
Staph aureus
Langerhans Cell in skin
Toll-like receptors (PRRs)
Phagocytosis and proceeding onto exogenous pathway.
Cellulitis.
Lymphoid tissue involved
Antigen presentation
Which T cells?
T cells to what cells?
Which adapted immune response?
SALT (Skin associated lymphoid tissue)
MHC class II
CD4+ T cells
To B cells
Humoral immune response
Respiratory infection due to adenovirus.
Give antigen presenting cells.
Sensors
Capture
Antigen processing pathway.
Dendritic cells
Toll-like receptors
The infection of the virus itself
Endogenous pathway
Adenovirus
Lymphoid tissue
Antigen presentation
T cells
T cells to what cells?
Adapted immune response.
BALT
MHC class I
CD8+ T cells
Cytotoxic T lymphocytes
Cell mediated response
