Antibacterial responses Flashcards
List some feature of bacterial infections
- In general, bacterial pathogens live and replicate in extracellular spaces with exceptions
- Several of the most acute and dangerous bacterial diseases are caused not by the bacteria themselves but by the toxins they produce
- Infection is an interaction between the pathogen and the host
- Key steps in infection: entry, invasion and colonisation of host tissue, evasion of immunity, tissue damage
Do all bacteria cause disease
- Bacteria do not always cause disease
- The intestine in a healthy adult contains about 10^14 essential bacteria
- With about another 10^12 on the skin
- Microbiota is a mechanism of protection to infection both ecological and immunological
List some general features of immunity to bacteria
- Innate and adaptive immunity
- Immune responds in specialised and different ways to different bacteria
- Pathogenicity and survival of the bacteria is critically influenced by the ability to evade the effector mechanism of immunity
- Latent bacteria are not cleared by immune system
- Tissue damage is associated with immunity and not infection
What are the first lines of defence against bacteria
- Skin
- GI tract
- Respiratory tract
- Urogenital tract
- Eyes
What are some components of the first lines of defence that help prevent bacteria
- Flow of fluid
- Sebum
- Enzymes
- Acidity
- Normal flora
What are anti-bacterial peptides: defensins
- 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.
- There are two types: a-defensins and β-defensins.
- a-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.
what happens if the initial barriers are crosses
- Activation of the complement pathway by microbial cell wall components
- The complement being a PRR
What is the complement system
- Key effector function of the humoral response.
- Serum and cell surface proteins that interact with one another to generate products that eliminate extracellular bacteria
What are the 3 pathways in the complement system
- Classical pathway - antibody activation
- Lectin pathway - MBL and carbohydrate activation
- Alternative pathway - Specific PAMP activation
What are the 3 functions of the complement
- Opsonisation and phagocytosis
- Stimulation of inflammatory reactions
- Complement-mediated cytolysis
Describe how opsonisation and phagocytosis work in the complement system
- Binding of C3b to microbe (opsonisation)
- Recognition of bound C3b by phagocyte C3b receptor
- Phagocytosis of microbe
Describe how stimulation of inflammatory reactions work in the complement system
- Binding of C3b to microbe
- release of C3a and C5a
- Recruitment and activation of leukocytes
- Destruction of microbes by leukocytes
Describe how complement-mediated cytolysis works in the complement system
- Binding of C3b to bacteria
- Activation of late components and complement
- Formation of the membrane attack complex
- Osmotic lysis of bacteria
Describe the role of complement receptors in phagocytosis
- Phagocytes express many complement receptors alongside other PRRs
- Allows them to recognise pathogens and undergo phagocytosis
- Also allows them to recognise bacterial components and produce cytokines in response
What are Pathogen Recognition Receptors (PRRs)
- Allows recognition of pathogens via many different kinds of receptors
- TLRs, scavenger receptors, Antibody receptors
