Host Defences Flashcards
2 types of host defences
Non specific
Specific
Why are non specific defences important?
—deal with most microbes
—without them animal would die before specific defence kicked in
List the barriers to infection and innate host defences
Phagocytic cells
Complement cells
—opsonise bacteria
—attract phagocytes to bacteria
—lose bacteria
Iron binding proteins
—starve microbes for iron
Anti-microbial peptides
—kill bacteria
What are NETs and how do they work
Neutrophil extracellular traps
-neutrophil encounters microbe & excrudes its nucleus & DNA producing a trap; traps microbe & stops it getting away, coating bacteria with antimicrobial components which kill microbe
What coats bacteria and makes them difficult to phagocytose?
Capsules
OPSONINS
Host molecules that attach to surface of bacteria for which phagocytic cells have receptors; tightly attach to organisms making much easier to phagocytose. capsulated/non capsulated microbe
2 types of opsonins
Innate
Acquired
What would happen if you placed a lab strain of bacteria into a tube containing mammalian serum?
Bacteria would be killed and lysed
Due to complement system
Conversion of complement C3/C5 into:
1.C3a, C5a, C4a
2.C3b, iC3b, C3dg, C4b
3.C5b6789. MAC
Each causes what?
- Promotes inflammation & recruitment of phagocytes
- Opsonisation (act as opsonins)
- Kill bacteria
How do host cells recognise foreign invaders?
Recognise conserved molecules present on many pathogens (microbes)
– Pathogen-associated molecular patterns (PAMPs)
– NB present on non-pathogens (MAMPs)
Recognise essential component
– little opportunity to vary
Bacterial molecules that have these characteristics
– Lipid A (LPS), G –ve bacteria
– Peptidoglycan, G +ve (G-ve) bacteria
– Bacterial DNA, all bacteria
– Bacterial lipoproteins, all bacteria
What are pattern recognition receptors
Present where
Receptors that allow rapid early detection of any pathogen
Recognise molecules found in pathogen
Present in cytoplasm, membrane of muscle etc etc
What is the effect of cytokines production by macrophages
Inflammation
Fever
TH2 T cell development
Acute phase response
TH1 T cell development
Enhanced IFNy production by TH1 T cells
B cell development
Attract neutrophils & T cells
Activation of M
What occurs once leukocytes encounter bacteria or their products
Encounter of leucocytes with bacteria or their products
>
Antigen processing etc
>
Activation, proliferation and differentiation of Lymphocytes
> —T helper cells (CD4+);
Provide help for B cells, Macrophage activation, Cytotoxic T cells
—Cytotoxic T cells (CD8+);
Lysis of infected cells
—B cells, plasma;
Produce antibodies
Functions of antibodies in bacterial infections
Anti transporter—> inhibit nutrient uptake
Anti capsules, anti LPS, anti surface antigen
—>opsonisation
Anti adhesins, anti invasins—> Inhibit adhesions and invasion
Anti toxins—> neutralise toxins
Complement activation—>opsonisation & bacteria killing
What do activated macrophages do?
Enhanced antibacterial activity
Enhanced respiratory burst- ^ROI (reactive 02 intermediates)
Production of nitric oxide
Enhanced phagocytose fusion
Enhanced secretion of pro-inflammatory cytokines
What are granulomas
a defensive mechanism that triggers the body to “wall off” foreign invaders such as bacteria or fungi to keep them from spreading
What is the role of TH1 T cells
Attraction and activation of macrophages
What is the role of TH2 T cells
Proliferation, differentiation and
maturation of B cells/Plasma cells, Mast cells and Eosinophils. Antibody secretion. Antibody class switching.
What is the role of TH17 T cells
Production and Attraction of PMN; activation of epithelial cell defences: Defence of surfaces.
Especially related to mucosal surfaces
Which cytokine do each of these T helper cells produce?
-TH1 cell
-TH2 cell
-TH17 cell
- IFNy
- IL-4
- IL-17
Cell mediated immunity means…
Activation of macrophages
Name 3 bacteria which have evolved to be able to grow within macrophages
Mycobacteria, Salmonella, Brucella
Macrophages need to be ‘activated’ to deal with pathogens by what cells…
TH1 cells
When a TH1 T cell binds to a macrophage to activate it, which 2 substances does it provide for macrophage
IFNy
Cell bound signals CD40 ligand and membrane bound TNFa
Which surface are TH17 T cells specifically produced on?
Mucosal surfaces
Which immune response would be relevant for an attack on pathogenesis of extracellular pathogens?
ANTIBODIES AGAINST SURFACE COMPONENTS (eg capsules, surface proteins) and secreted proteins (eg toxins)
Which immune response would be relevant for an attack on pathogenesis of intracellular pathogens?
Cell mediated immunity (CMI): Th-1 cells, activation of macrophages
– Antibodies may play little or no role
– Th-17 response known to be involved in some of these infections.
What happens when T helper cells TH1 and TH2 negativey cross regulate each other
IFNy produced by TH1 cells can inhibit TH2 cells
And
IL-4 produced by TH2 cells can inhibit TH1 cells
During this, it is usually found that one response is major whereas they other is minor, both happen at the same time however. This means that there is a lot more of one T cell rather than the other.
What happens when T helper cells cross regulate one another in an extreme way?
Infections like leprosy in humans can occur
