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Immunology 1: Natural defences + Innate immune response (i) (Natural…
Immunology 1: Natural defences + Innate immune response (i)
intro
immune system functions
defence against infection
non-specific
innate
adaptive
surveillance
removal of tumour cells
challenges for immune system
bugs vary in shapes + sizes
bugs evolve rapidly, so immune system must do so too
must recognise billions of pathogens
must avoid friendly fire (autoimmunity) - must distinguish self + non-self
pathogens
mycobacteria
in vesicles
intracellular
have tough waxy outer coat
hard to be digested
viruses
intracytoplasmic
bacteria
most are extracellular
fungi (variable size)
protozoa (e.g. giardia)
unicellular
extracellular
larger than bacteria
nematodes
(e.g. ascaris)
v big
Natural defences
highly effective but frequently breached in sick patients (e.g. ICU)
incubated patient, multiple natural defences bypassed
skin
mechanical barrier
dry
high salt content (prevents pathogens thriving)
has commensal resident flora (e.g. S epidermis) - no space or nutrients left for pathogens - ! killed by antibiotics
has transient flora (e.g. s aureus, e coli) that are removed by hand washing
! sepsis @ surgical sites, line/tube insertion sites
aspects of normal body structure + function, non-specific
resp tract
nasal hairs, mucus, lysozymes
normal flora (killed by antibiotics)
ciliated epithelium (damaged by smoking/inflamm)
mucociliary elevation: normal mucous:ciliated cell ratio = 1:9, but changes to 1:1 - more mucus, isolated cilia
cough + sneeze reflexes (! muscles paralysed when on a ventilator -> ventilator-associated pneumonia)
eyebrows + lashes
prevent foreign bodies + dirt entering the eye
lacrimal fluid
contains lysozyme
blink reflex
NB as eye infections are hard to treat (poor penetration by antibiotics)
GUT
free flow of urine with dilution NB
lysozyme in bladder
catheters increase infection risk
recurrent GUT infections usually due to obstructive local problem (e.g. stones/tumours)
vagina = acidic (pH5) due to glycogen metabolism by lactobacilli (killed by antibiotics: secondary vaginosis + thrush)
GIT
stomach acid
often drained once patient is in shock, infection once patient eats again
peristalsis: diarrhoea (increased peristalsis to expel pathogen
normal flora (esp anaeobes)
colicins (bacteriocin produced by E coli, reduce competition from other bacterial strains) + short chain FAs
bacteriocin = protein produced by bacteria of one strain and active against a closely related strain
broad spectrum antibiotics kill commensals in gut lumen -> C diff infection
produces toxin that kills enterocytes + causes mucosal injury
neutrophils + RBCs leak out -> profuse bloody diarrhoea