Immune Defence against Bacteria Flashcards
(28 cards)
How do neutrophils and macrophages fight against bacteria?
- Phagocytosis
- Secretion of antimicrobials like reactive oxygen species
- Release of extracellular traps (NETs and sometimes METs for macrophages)
What do NK cells do against bacteria?
Kill host cells infected with INTRAcellular bacteria (e.g. Listeria)
What do mast cells do against bacteria?
Promote inflammation and recruit neutrophils
What is the role of CD4+ Th1 cells in fighting bacteria infection w/ example?
Th1 cells produce IFN-y, which can activate macrophages from naive (M0) to M1 macrophages.
Important in control of intracellular bacteria like M. tb and Listeria
What cytokines do Th17 cells secrete?
IL-17 (and IL-22)
What is the role of IL-17 in bacterial immune defence?
Central role in immunity to extracellular bacteria:
- Promotes production and recruition of neutrophils
- Important in barrier defence (particularly mucosal and epithelial surfaces)
Example of extracellular bacteria for which IL-17 is important in clearing
Staphylococcus aureus
What are the two types of adaptive immunity?
- Cell-mediated immunity (T & B cells)
- Humoral immunity (antibodies)
What are the main roles of humoral immunity against bacteria?
- Neutralisation
- Opsonisation
- Complement activation
- Agglutination
What antibody subclass are involved in neutralisation?
IgG, IgM and IgA (less potently)
What does neutralisation mean?
Antibodies bind to bacterial adhesins or secreted toxins. This prevents:
- Attachment to host cells
- Toxin entry into host cells
What is an example of an antibody neutralisation target?
Antibodies can bind to Neisseria pili, preventing them from attaching and entering host cells
How does opsonisation work?
IgG (which is an opsonin) binds to phagocyte, marking it for phagocytosis.
Fc region of bound IgG is recognised by Fcy receptors on phagocytes
What is the result of opsonisation, and for which bacteria is this crucial?
Opsonisation increases phagocytic uptake and bacterial killing.
It is particularly crucial for encapsulated bacteria (that resist direct phagocytosis)
What are some examples of encapsulated bacteria that resist direct phagocytosis?
- S. pnumoniae
- Neisseria meningitidis
What antibodies are responsible for activation of the classical complement pathway?
IgM(1) and IgG(3)
What is agglutination?
Where antibodies crosslink bacterial cells, leading to clump formation and easier clearance by phagocytes
What complement component is involved in opsonisation?
C3b
What complement component is involved in chemotaxis?
C5a- recognised by complement receptor 1 (CR1) on neutrophils and monocytes.
Crucial for phagocytosis of encapsulated bacteria
How does the membrane attack complex defend against bacteria?
MAC can directly lyse Gram-negative bacteria- Gram positive are more resistant due to thicker peptidoglycan
What complement component is involved in Membrane Attack Complex formation?
C5b-C9. Assemble to form a pore in bacterial membranes
What is the role of complement component C3d?
Binds antigen and is recognised by complement receptor 2 (CR2) on B cells.
Enhances b cell activation
What can a C5-C9 deficiency lead to?
No MAC, so increased risk of Gram negative infection e.g. Neisseria
What cells does IL-17 work on?
- Epithelial/stromal cells
- Endothelial cells
