Host Defence Mechanisms Flashcards
what are the 4 genres of host defence mechanisms?
- normal flora
- mechanical processes
- Immune system
- physical barriers
name 5 physical barriers
- tears- lysozyme
- Skin- dry, acidic, sweat containing fatty and lactic acid.
- filtration of inhaled air by turbinate bones.
- commensal bacteria in GI and skin
- acidity of stomach and vagina
what is the hosts mechanical defences?
Mucociliary action and Flushing
whats Mucociliary action?
mucous prevents attachment and is pushed to the throat by ciliated epithelia.
define flushing
flow of fluid over mucosal surface removing bacteria.
give some exiles of flushing?
- urine flow over urogenital tract
- gut contents in GI tract
- tears over cornea
how is the normal human flora a defence mechanism?
- exclude colonisation by competition
- induce low level antibody and react with the pathogen
- produce antimicrobials bacteriocin and fatty acids.
explain 4 ways the hosts immune system acts as a defence?
- inhibitory compounds
- specialised immune cells
- secretory immunity
- systemic immunity via Ab
name 5 inhibitory compounds
- HCL - stomach
- Bile salts and fatty acids.
- Defensins
- Lactoferrin and transferrin
- Lysozyme.
whats the action of lysozyme?
cleaves peptidoglycan and disrupts the cell wall found in saliva and tears
whats the action of Lactoferrin?
found in body secretions and serum binds to free iron so inaccessible to bacteria.
whats the action of Defensins?
pore forming cationic peptides
name the specialised immune cells that are involved in the hosts defence
phagocytic cells, Kupffer cells mesagnial cells and alveolar macrophages
name the cells of the reticuloendothelial system
lung- alveolar macrophages
kidney- mesagnial cells
liver- Kupffer cells
peridontal tissue- gingival macrophage.
describe secretary immunity
- sIgA inhibits bacterial attachment to mucosal epithelium.
- agglutinates bacteria
- binds inactive toxins
- presents in colostrum so protects suckling infants.
define virulence
the potential for a pathogen to produce morbidity or mortality in infected hosts
define virulence factors
properties that enable a microorganism to establish itself on/within a host of a particular species + enhance its potential to cause disease.
name the 8 bacterial virulence factors
- capsule
- fimbriae
- type III secretion system
- siderophores
- endotoxin
- toxins
- biofilms
- serum resistance
how does the capsule protect the host?
surface polysaccharides protect against host immune defence
how does serum resistance protect the cell?
surface molecules mediate resistance to complement
how do biofilms protect bacteria?
attachment and persistence
how do toxins protect the cell?
secreted (exo) or membrane bound (endo) proteins cause tissue damage or inhibit tissue function.
how do siderophores protect bacteria?
scavenge iron and promote uptake into bacteria
name an endotoxin and how it works
lipopolysaccharides are components of membranes elicit immune/inflammatory response.
how is fimbriae a virulence factor?
adheres to host tissues and is subject to Ag variation.
how do type III secretion systems work?
adherence to and invasion of host tissues
what are the 6 stages if bacterial infection?
- entry
- colonisation
- proliferation
- invasion
- immune evasion
- transmission
how does entry occur?
- skin is major barrier breached by bites and wounds
2. entry via mucosal surfaces
what is colonisation?
attachment to mucosal surfaces
what is proliferation?
acquisition of nutrients and overcoming Fe limitation
what is invasion?
entry into host tissue/cell local/systemic
what is immune evasion?
avoidance of the immune system via Ag/phase variation and resistance to immune effects.
whats the prevalence of UTI?
10-20% woman 12% men
what causes UTI?
90% E. coli
how do you treat UTI?
oral ampicillin or IV gentamicin
how does UTI infection occur?
contamination by bacteria from the GI tract
describe the virulence factors present in Neisseria meningitides
- capsule
- LPS
- pilus
4 Tbp, Lbp, Hpu, HmnR, FetA - Opa, Opc, NhhA, NadA.
