S2: the microbiome & innate immunity Flashcards
Describe the infection model
Patient Pathogen Mechanism of infection Process of infection Management of the patient Patient outcomes
Name some microbes commonly found on the skin
Staphylococcus aureus
Staphylococcus epidermidis
Streptococcus species
Define innate immunity
Innate immunity is one part of the immune response – it is a fast, non-specific immediate response to any foreign pathogen that breaks the lines of defence.
What are the 4 innate barriers?
Physical barriers eg. skin, mucosal membrane
Physiological barriers eg. vomiting, coughing
Chemical barriers eg. low pH, antimicrobial molecules
Biological barriers eg. normal flora
How do infections arise?
1) normal flora is displaced from its usual location to
another environment which may be sterile
2) the host becomes immunocompromised and the normal flora can start to overgrow and become pathogenic
3) when normal flora is depleted due to antibiotic treatment
What is the second line of defence?
1) phagocytes = macrophages, monocytes, neutrophils
2) other key cells of the innate immune system = basophils (mast cells), eosinophils, natural killer cells & dendritic cells
3) chemicals = complement system and cytokines
Causes inflammation
How are pathogens recognised by cells of the innate immune system?
On microbial structures there are pathogen-associated molecular patterns (PAMPs): carbs, lipids, proteins, nucleic acids
On phagocytes there are pathogen recognition receptors (PRRs): toll like receptors
What is the opsonisation of microbes?
Opsonisation of microbes enhances the interaction between the phagocyte and the microbe.
Opsonins = proteins that bind to and coat the surface of the microbe.
These are produced by various components of the immune system – complement proteins, antibodies, and acute phase proteins
What are the two different pathways by which a phagocyte destroys a microbe?
Oxygen-dependent pathway = free oxygen radicals
Oxygen-indepedent pathways = enzymatic digestion
What is the complement system?
Complement system proteins circulate in the blood as inactive precursors which are activated in a cascade fashion culminating in phagocyte activation and microbe digestion
Name important complement system proteins and their functions
1) C3a/C5a – which are responsible for recruitment of phagocytes
2) C3b/C4b – opsonisation of pathogens
3) C5 – C9 – killing of pathogens
What are the different pathways that are activated in the complement system?
Classical pathway = intitiated by antibody-antigen pathway
Alternative pathway = initiated by cell surface microbial constituents
MBL pathway = initiated when MBL binds to mannose containing residues of proteins found on many microbes
What is the role of cytokines in innate immunity?
They have a role to play in inflammation and so called cytokine storms occur when the immune system essentially overreacts and triggers a cascade of events which may culminate in death
What are the different mediators released at each stage of innate immunity?
Vasodilatation – histamine + serotonin Increased vascular permeability – histamine + bradykinins Chemotaxis – C5a + LTB4 Fever – prostaglandins +IL-1 Pain – bradykinin + Substance P
