10 - The Humoral Arm Of Innate Immunity Flashcards
What type of growth of bacteria show
Exponential
- linear log graph shown
Why is early exponential growth in bacteria dangerous
- what can be done to prevent this
- adaptive immune response takes 7-10 days to activate
- so we rely on our innate immune system for protection in the first few critical hours or days after pathogen challenge
Three lines of innate immune system defence
- give examples of each
- barriers - physical and chemical
… - cell-intrinsic responses
… - specialised proteins and specialised cells
…
Mucus layer function and info
- acts as a physical and chemical barrier against pathogens
- protects against microbial, mechanical and chemical dangers to the body
- made from secreted mucins and other glycoproteins
- it is slippery - hard for pathogens to attach to mucus-coated epithelia
- usually found with ciliates epithelial cells
- found in fish and many amphibians that produce mucus layer on their skin (e.g. hagfish)
Mucus layer structure
- Made from secreted mucins and other glycoproteins
- contain defensins
Defensins info and function
- are small positively-charged antimicrobial peptides
- have hydrophobic or amphipathic helical domains
Function: - wide anti-microbial activity
- can kill or inactivate:
- gram +ve or -ve bacteria
- fungi, including yeasts
- parasites, incl. Protozoa and nematodes
- enveloped viruses such as HIV
How do defensins work
- mechanism is uncertain
- hydrophobic domains or amphipathic helices may enter into core of lipid membrane of pathogen and destabilise it, lead to cell lysis
- following membrane disruption, +ve charges may interact with -ve nucleic acids in pathogen
- they are much more active on membranes that don’t contain cholesterol (our membranes contain cholesterol
- relatively non-specific, so difficult for pathogens to acquire resistance
If pathogens breach epithelial barriers, how does innate immune system recognise them as non-self
- recognises molecules common to many pathogens, which are essentially absent in host
- these are called PAMPs - pathogen-associated molecular patterns
PAMPs info
Various classes of PAMPs recognised by human cells:
- fMet used for bacterial translation initiation - attract neutrophils
- peptidoglycan forms cell walls in bacteria
- bacterial flagella
- LPS from gram-negative bacteria
- mannans, glucans and chitin from fungi
- CpG motifs in bacterial or viral DNA
Pattern recognition receptors (PRRs) info and diagram
Complement activation pathogen lysis targeting pathway
- outline this pathway
Lectin pathway:
- mannose and fructose binding proteins used
- early complement components are proenzymes
- these activate next member in line by cleavage
- results in amplified proteolytic cascade
- pivotal proteolysis is the one that cleaves C3 into C3a and C3b
- C3a calls for help
- attracts phagocytes and lymphocytes
- stimulates inflation
- C3b binds covalently to the pathogens plasma membrane
- pathogen-bound C3b stimulates a local cascade of reactions (C5-C8) at the marked membrane
- C9 is inserted into the membrane
- Pathogen lysis occurs
4 parts of innate immune system
