Lecture 6 - Bacterial immunity Flashcards
Describe the main innate responses to bacteria Have a more detailed understanding of mechanisms by which phagocytes kill bacteria Describe the main adaptive responses to bacteria
What sort of molecules are recognised by the innate system?
Molecules that are common to bacteria but absent from the host (PAMPS)
What is the membrane attack complex?
C9 forms a pore and inserts into bacterial cell membranes. It promotes cell lysis.
A deficiency in C1q of the complement cascade, leads to increased susceptibility to what?
Sepsis, meningitis, pneumonia
A deficiency in C3 of the complement cascade, leads to increased susceptibility to what?
Respiratory tract infections and meningitis
A deficiency in C5 of the complement cascade, leads to increased susceptibility to what?
Meningitis and sepsis
A deficiency in C9 of the complement cascade, leads to increased susceptibility to what?
Meningitis and sepsis
What is involved in the process of indirect bacterial recognition?
Bacteria coated with antibodies are recognised by AB receptors (e.g. Fc receptors)
*Bacteria coated with C3b are recognised by C3b receptors
What is involved in the process of direct bacterial recognition?
PAMPs are recognised by PRRs e.g. TLRs
Describe the rough structure of a TLR (toll like receptor)
They have an extracellular domain required for ligand recognition and an intracellular domain for signalling.
*dimerisation is also essential for signalling
What are the consequences of binding to phagocytes?
Activation of pathways leading to cytokine and chemokine production
Ingestion and killing
What is the action of IL-1?
Activates endothelial cells and important in fever
What is the action of IL-6?
Proliferation of AB producing B cells
What is the action of TNF-a?
Activates endothelial cells, important in fiver and activates neutrophils
What is the action of INF a?
Antiviral immunity, promotes CD4 and CD8 T cell responses
What is the action of IFN b?
Antiviral immunity, promotes CD4 and CD8 T cell responses
What is the name of the process by which bacteria recognised by TLRs are killed?
Phagocytosis
What are the 5 steps in the process of phagocytosis?
- Bacteria recognised by phagocyte via its TLR
- Recognition triggers uptake of bacteria into phagosome, where bacterial killing takes place.
- This phagosome fuses with a lysosome to form the phagolysosome
- The internalised bacteria is broken down in the phagolysosome
- Soluble debris are released via exocytosis
What does the adaptive system recognise?
Antigens (motifs) that are unique to an individual pathogen, most commonly proteins and polysaccharides
Name 4 bacterial diseases where CD8 T cells play a role in protection
Tuberculosis
Salmonellosis
Listeriosis
Meliodosis
What are the downstream affects of CD4+ t helper cell activation?
Il-17 and TNF (amongst others) cause inflammation
IFNg causes macrophage activation which leads to phagocytic bacterial killing
Various cytokines activate B cells/ plasma cells in order to produce an AB response
What is agglutination?
Antibodies mark bacterial cells and cause them to stick together (agglutinate) meaning they are more efficiently cleared by phagocytes
What is neutralisation?
ABs are capable of binding to and ‘neutralising’ toxins. If toxins are central to the disease process then ABs that neutralise the toxin block the disease
What is opsonisation?
Antibodies bind to bacteria and make them more ‘visible’ to phagocytes. ABs bound to bacteria promote their uptake and killing by phagocytosis.
