Innate Immune System Flashcards
What innate immune system acts as the first line of defence, what are these defences?
Physical barriers Physiological barriers
Chemical barriers
Biological barriers
*these all prevent entry and limit growth of pathogens
Give some examples of the physical barriers that have a role in the innate immune system.
- skin
- mucous membranes; mouth, respiratory tract (*), GI tract, urinary tract
- bronchial cilia (can catch and move pathogens)
*lower resp tract should be sterile
Give some examples of the physiological barriers that have a role in the innate immune system.
- diarrhoea; food poisoning
- vomiting; food poisoning, Hep, meningitis
- coughing; pneumonia
- sneezing; sinusitis
Give some examples of the chemical barriers that have a role in the innate immune system.
- low pH; skin (5.5), stomach (1-3), vagina (4.4)
- antimicrobial molecules; IgA (tears, saliva, mucous membrane), lysozymes (sebum, perspiration, urine), mucus (mucus membranes-highly toxic for gram +/-), beta-defensins (epithelium), gastric acid and pepsin
Give some examples of the physical barriers that have a role in the innate immune system.
- normal flora; non pathogenic microbes, endogenous, strategic locations (where pathogens can enter ie mouth, skin, vagina etc), absent in internal organs/tissues
Flora can complete with pathogens for attachment site and resources
They can produce antimicrobial chemicals (endotoxins) and synthesise vitamins (K, B12 etc)
How might normal flora get into the wrong place?
Breaching the skin integrity; skin loss (burns), surgery, injections, IV lines
Faecal-oral route; foodborne infection
Faecal-perineal-urethral route; UTI (women)
Poor dental hygiene/dental work
What patients are at increased risk of infections?
Asplenic (and hyposplenic) patients
Patients with damaged or prosthetic valves
Patients with previous infective endocarditis
How can normal flora cause clinical problems?
- When it is depleted by antibiotics
- When it overgrows and becomes pathogenic when host is immuno-compromised
- When it is displaced from its normal location
- When the flora is displaced from its normal location to sterile locations
What is the second line of defence that the innate immune system has?
Phagocytes and chemicals (ie complement system and cytokines)
Which lead to inflammation
These factors will contain and clear the infection
What are the main phagocytes that work in innate immunity?
Macrophages (all organs)
Monocytes (blood)
Neutrophils (blood)
What is the macrophages role in innate immunity?
Phagocytosis
Present microbial antigens to T cells (adaptive immunity)
Produce cytokines/chemokines
What is the role of monocytes in innate immunity?
Recruited at infection site and differentiate into macrophages
What is the role of neutrophils in innate immunity?
Increased during infection
Recruited by chemokines (from macrophages) to site of infection
Phagocytose pyogenic bacteria (staph A and strep pyogenes)
What are other key cells in innate immunity (those that aren’t involved in phagocytosis)? What are their functions in innate immunity?
Basophils/mast cells- early actors of inflammation (vasomodulation) and important in allergic responses
Eosinophils- defence against multi-cellular parasites (worms)
NK cells- kill all abnormal host cells (virus infected/ malignant)
Dendritic cells - present microbial antigens to T cells (acquired immunity)
How can a phagocyte recognise a pathogen? (Hint; What do the cells have)
Phagocytes have PRR (pathogen recognition receptor)
Pathogens each have a PAMP (pathogen associated molecular pattern)
These can match and the cell knows what is the pathogen
