Antibacterial Responses Flashcards
Key steps in infection
entry, invasion and colonisation of host tissue, evasion of immunity, tissue damage
Why is the microbiota important?
It is a mechanism of protection to infection both ecological and immunological
This shows that not all bacteria cause disease
How do bacteria survive in the body?
by the ability to evade the effector mechanism of immunity
Some bacteria establish latent or persistent infection and the immune system does not clear the microbe
Give examples of the mechanical defence of different organs
(flow of fluid)
(Epithelial cells joined by tight junctions)
Skin - perspiration, sloughing off of skin
GI tract - mucus, food and saliva
Respiratory tract - mucus and by cilia air flow
Urogenital tract - urine, mucus, sperm
Eyes - flow of fluid tears
Give examples of the chemical defence of different organs
Skin - sebum (fatty acids, lactic acid, lysozyme)
GI tract - acidity, enzymes (proteases)
Respiratory tract - Lysozyme in nasal secretions
Urogenital tract - Acidity in vaginal secretions, spermine and zinc in semen
Eyes - lysozymes in tears
Give examples of the microbiological defence of different organs
Normal flora of the named organ
Anti-microbial peptides
capable of killing by penetrating microbial membranes thus disrupting their integrity.
They are active against bacteria, fungi and many enveloped and non-enveloped viruses.
Types of Anti-microbial peptides
𝛂-defensins and β-defensins.
𝛂-defensins are secreted mainly by neutrophils and by Paneth cells
β-defensins are secreted by a broad range of epithelial cells, in particular, those in the respiratory tract, the skin and the urogenital tract.
How do toxins work?
Binds to cellular receptors
Endocytosis of toxin/receptor complexes
Dissociation of toxin to release active chain, poisoning cell
The complement system
Key effector function of the humoral response.
Serum and cell surface proteins interact with one another to generate products that eliminate extracellular bacteria
What are the complement pathways?
What activates the pathways?
Classical - Antibodies
Lectin - Carbohydrate
Alternative - Specific PAMPs
the function of the antibodies
• Neutralise bacterial toxins
• Trigger classical complement pathway by
binding of IgM to the bacterial cell surface
• Opsonisation; coating of bacteria with
antibody thereby aiding phagocytosis
What does complement cause?
Inflammation, lysis and opsonisation
Toxin neutralisation
• Many bacteria secrete protein toxins that cause disease by
disrupting the normal function of host cells
• In order to do this a bacterial toxin must bind to a receptor
• Thus, antibodies that bind to that receptor block the function of the toxin
Triggering of the complement cascade
- IgM bound to the surface of a bacterium binds to a complement component that initiates the classical pathway of complement activation.
- As a consequence of this, the bacterial cell surface is coated in C3b facilitating its phagocytosis.
What do neutrophils do?
Neutrophils perform phagocytosis and degranulation of granules- the intracellular killing of bacteria
Oxidative burst kills the bacteria
Neutrophils Extracellular Traps (NETS)
What do pattern recognition receptors (PRRs) and PAMPs lead to?
Phagocytosis and the production of cytokines:
PAMP binding by PRRs activates the phagocyte
Phagocyte ingests microbes, enlarges and increases metabolic activity
Activated phagocytes elevate antimicrobial activity
If infection is detected through TLRs, pro-inflammatory cytokines(eg IL1 Il6 and Tnf-alpha) and chemokines are produced, leading to the initiation of an inflammatory response.
How do helper T cells enhance the phagocytosis of extracellular pathogens?
Helper T cells enhance phagocytosis of extracellular pathogens by activating macrophages
The MHC class II pathway presents bacterial antigens derived from extracellular infections to helper CD4 T cells
- Macrophage engulfs and degrades bacterium, producing peptides.
- Bacterial peptides are bound by MHC Class II in vesicles.
- Bound peptides are transported by MHC Class II to the cell surface.
- Helper T cell recognises complex of peptide antigen with MHC Class II and activates macrophage.
Overall, what is involved in innate immunity and adaptive immunity?
The innate immune response to bacterial infection:
Complement
Pattern recognition of bacteria Phagocytosis Opsonisation Cytokine secretion Inflammation
The adaptive immune response to bacterial infection
CD4+ and CD8+ T cells
Antibodies
