Innate Immune System Flashcards
What are the three factors that determine the outcome of the host -pathogen relationship?
1) infectivity
2) virulence
3) host immune response
What is infectivity
The ability for the microbe to attach itself within the host cell or on the host cell
What is virulence
Capacity for microbe to do some damage
What is the host immune response
The patients immune response - for example it is different in pregnant women , children and elderly
Define the immune system
Cells and organs that contribute to defences against infectious and non infectious conditions
What is an infectious disease
When the pathogen succeeds in evading /or overwhelming the hosts immune system
What is the immune system divided into
1) innate immunity
2) adaptive immunity
What are features of innate immunity
1) first line of defence
2) immediate protection
3) fast ( within seconds )
4) lack of specificity
5) lack of memory
6) no change in intensity
For example , the skin acts as an innate immunity barrier to pathogens and phagocytosis
What are features of adaptive immunity
- long lasting protection
- second line of defence
- it is highly specific
- it is very slow ( takes a couple days )
- provides immunological memory ( memory T and B cells )
- changes in intensity
What is the outcome e of innate immunity and adaptive immunity ?
Protection
What are examples of innate immunity defences?
1) physical , physiological , chemical , biological barriers
Which are factors that prevent entry and limit growth of pathogens
What are examples of physical barriers ?
1) skin
2) mucous membranes in the mouth , respiratory tract and GI tract , urinary tract
What are examples of physiological barriers ?
1) diarrhoea - helps to expel microbe out
- vomiting : expels microbe ( eg food poisoning , hepatitis , meningitis )
- coughing ( eg in pneumonia )
- sneezing ( sinusitis )
What are examples of chemical barriers ?
LOW PH in the skin (5.5)
- stomach (1-3)
- vagina (4.4- this induced lactobacillus which secretes lactic acid)
2) antimicrobial molecules eg IgA ( in tears , saliva , mucous membranes which prevents the microbe attaching to the host ). Also lysosomes which is produced in sebum , urine. Mucus which traps all the microbe. Beta defensins ( they act in a non specific manner - produced in epithelium) . And gastric acid is very acidic so microbes cannot survive here,
What are examples of biological barriers
1) flora which are non-pathogen microbes
- they are found in mucus membrane areas eg skin , GI tract , vagina , mouth. Throat
- they are ABSENT in internal organs and tissues
- they compete with pathogens for attachment sites and rescources. Produce antimicrobial chemicals. They also synthesise vitamins ( K, B12, other B vitamins).
- also allow for immune maturation
What occurs when normal flora is displaced from its normal location to sterile location ?
- 1) fecal-oral route ( where flora from faeces enters the mouth)
2) fecal-perineal-urethral route ( where flora from the anus enters the vagina ) causes UTI
3 ) breaching the skin integrity eg through skin diseases , skin loss due to burns , IV lines , injecting drug users , tattooing g
4)poor dental hygiene
What type of patients have a high risk of serious infections ?
1) asplenic and hyposplenic patients
2) patients with damaged or prosthetic valves
3) patients with previous infective endocarditis
What are a few causes of when flora over grows and becomes pathogenic ?
1) patients with diabetes
2) patients with AIDS
3) malignant diseases
4) chemotherapy
What are a few examples of normal flora in mucosal surfaces depleting due to antibiotics?
1) in vagina which causes thrush.1) taking antibiotics can kill the lactobacillus bacteria in the vagina ( this is used to help keep the vagina at a pH of 4.4 - with this occurring this disrupts the natural flora present in the vagina allowing other pathogenic yeast to grow for example Candida albicans)
2) In the intestine , taking antibiotics can allow other bacterium’s to flourish, for example clostridium difficult which causes severe colitis.( severe inflammation of the inner lining of the colon)
Where are macrophages found ?
Present in all organs
What is the role of macrophages ?
They ingest and destroy microbes by phagocytosis
- they present microbial antigens to T cells
- they produce cytokines /chemokines
Where are monocytes found ?
In the blood (5-7%)
What is the role of monocytes ?
- recruited st an infection site and differentiate into macrophages
Where are neutrophils found ?
In the blood (60%)
What increases in number during infection ?
Neutrophils
What is the role of neutrophils ?
Recruited by chemokines to the site of infection
- they ingest and destroy phonemic bacteria
What is the role of eosinophils ?
Defence against multi cellular parasites ( worms )
What is the role of basophils/mast cells?
- they are important in allergic responses
- they are the early actors of inflammation because they contain different granules of substances eg histamine and heparin.
What is the role of dendritic cells ?
Present microbial antigens to T cells ( acquired immunity)
What are opsonins
Coating proteins that bind to microbial surfaces leading to enhanced attachment of phagocyte and clearance of microbes
- phagocyte have the opsonin receptor
Why is measuring the concentration of C-reactive protein important?
It is an inflammatory marker
What is the most important function of the spleen ?
They are very important in recognising the encapsulated bacteria and clearing them from the body.
- for example meningitis
- encapsulated bacteria often cause invasive infections
What are natural killer cells ?
They kill all abnormal host cells - this can be virus infected or malignant
How are pathogens recognised by phagocytes ?
Phagocytes have pathogen recongition receptors (PRRs) which are ‘ roll like receptors’ that recognise PAMPS ( pathogen associated molecular patterns).
Give an example of a type of pathogen recongition receptor and which type of bacteria it recognises ?
TLR4 recognises lipopolysaccharide (gram negative bacteria )
TLR2 recognises lipoproteins and lipopeptides ( gram negative bacteria )
TLR2 also recognises peptidoglycan gram positive bacteria
TLR4 also recognises lipoteichoic acids ( gram positive bacteria )
Give a few examples of opsonins
1) complement proteins (C3b and C4b)
2) antibodies : IgG and IgM.
3) acute phase proteins ( C-reactive protein & mannose-binding lectin)
Outline the process of phagocytosis
1) chemotaxis and adherence of microbe to phagocyte
2) ingestion of microbe by phagocyte
3) formation of phagosome
4) fusion of phagosome with a lysosome to form a phagolysosome
5) digestion of ingested microbe by enzymes
6) formation of residual body containing indigestible material
7) discharge of waste materials
What are the two mechanisms used by phagocytes to intracellularly kill microbes ?
1) oxygen dependant pathway ( respiratory burst)
2) oxygen independent pathways
What is the oxygen dependant pathway ?
- it is a mechanism where phagocytes kill microbes intracellularly
- oxygen free radicals : h202, Oh*-, nitric oxide , singlet oxygen and hypohalite are used to kill microbes
What is the oxygen independant pathway
Mechanism phagocytes used to kill pathogens intracellularly
- use of lysosomes
- lactoferrin/transferrin
- hydrolytic enzymes /proteolytic enzymes
What are examples of when phagocytosis may be reduced ?
1) decreased spleen function : this can be in asplenic patients or hyposplenic patients
2) decreased neutrophil number : this can be in cancer chemotherapy patients , certain drugs ( phenytoin) and leukaemia and lymphoma
3) decreased neutrophil function : chronic granulomatous disease ( no respiratory burst) and chediak -higashi syndrome ( no phagolysosomes)
What is the complement system ?
Is a complex of soluble proteins present in the serum that are capable of sensing microbes and activation a chain of enzymatic chain reactions leading to the activation of various complement proteins with different anti microbial properties.
The main products are : C3a-C5a, C3b-C4b , C5-C9
