innate Immune System Flashcards
(39 cards)
Describe the different innate barriers to infection
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What are the three main factors determining the outcome of the host- pathogen relationship?
1) Infectivity - The capacity of the pathogen to establish itself within the host
2) Virulence - Capacity of microbe to actually damage the host
3) Host immune response
What is the immune system?
Cells and organs that contribute to immune
defences against infectious and non-infectious conditions (self vs non-self)
What is an infectious disease?
When the pathogen succeeds in evading and/or overwhelming the host’s immune defences
What are the roles of the immune system?
- Pathogen recognition = Cell surface and soluble receptors
- Containing/eliminating the infection = Killing and clearance mechanisms
- Regulating itself = Needs to be stopped eventually to ensure minimum damage to host (resolution)
- Remembering pathogens = Preventing the disease from recurring
What is the difference between innate immunity and adaptive immunity?
Innate Immunity: Immediate protection • Fast (within seconds) • Lack of specificity • Lack of memory • No change in intensity
Adaptive Immunity: Long lasting protection • Slow (days) • Specificity • Immunologic memory • Changes in intensity (Faster and stronger)
You cannot have adaptive immunity if innate immunity has not been activated.
What are the first lines of defence in innate immunity?
Factors that prevent entry and limit growth of pathogens
- Physical barriers
- Physiological barriers
- Chemical barriers
- Biological barriers
If there is anything that is affecting or preventing the integrity of these innate barriers then the patient will have an increase in infection susceptibility.
What are some physical barriers to pathogens?
• Skin (surface area 1-2 m2)
- Mucous membranes - in body cavities, dynamic, can sense the pathogens and initiate immune response because they have a high number of immune cells. They can be found:
- Mouth
- Respiratory tract
- GI tract
- Urinary tract
• Bronchial cilia - remove any trapped microorganisms from mucous outside the lung that will be expelled out of lung or swallowed e.g. Problem in CF
What are some physiological barriers to pathogens? Give an example of when each of them are used.
• Diarrhoea
- To expel the microorganisms e.g. Food poisoning
• Vomiting
- Again, to expel the microorganism e.g. Food poisoning
- Hepatitis
- Meningitis
• Coughing
- Pneumonia
• Sneezing
- Sinusitis
What are some chemical barriers to pathogens? Give an example of when each of them are used.
• Low pH
- Skin (5.5)
- Stomach (1-3)
- Vagina (4.4) - caused by bacteria called lactobacillus
• Antimicrobial molecules
- IgA (Tears, saliva, mucous
membrane )
- Lysozyme (sebum,
perspiration, urine)
- Mucus (Mucous membranes, can trap microorganisms so they can be expelled)
- Beta-defensins (toxic to gram positive and negative bacteria epithelium)
- Gastric acid + pepsin (kills almost all microorganisms)
How can antibiotics lead to vaginal thrush?
In the vagina, there are opportunistic fungi that are there but do not grow.
If a patient is treated with antibiotics, you kill the normal flora there that maintain the low pH and so the fungi can now thrive as the pH is high enough for them to grow
How does Immunoglobulin A work?
Binds to microbe and prevents it from attaching to the mucous membrane of cells
Since the microbe cannot attach, it will not be able to grow
What are some biological barriers to pathogens? Give an example of when each of them are used.
As long as they do not move from their designated places, they are fine.
Should not be in blood, organs or tissues.
• Normal flora
- Non pathogenic microbes
- Strategic locations
- Nasopharynx
- Mouth/Throat
- Skin
- GI tract
- Vagina (lactobacillus spp)
- Absent in internal organs/tissues
• Benefits - Compete with pathogens for attachment sites and resources. - Produce antimicrobial chemicals -Synthesize vitamins (K, B12, other B vitamins).
Name two examples of normal flora that inhabit the skin and the nasopharynx.
Skin:
• Staphylococcus aureus
• Staphylococcus epidermidis
Nasopharynx:
• Streptococcus pneumoniae
• Neisseria meningitidis
They are opportunistic normal flora that could become pathogenic in certain cases.
When do normal flora become clinical problems?
1) Normal flora is displaced from its normal location to sterile location
• Breaching the skin integrity
- Skin loss (burns)
- Surgery
- Injection drug users
- IV lines
• Fecal-oral route
- Foodborne infection, food is contaminated by fecal matter
• Fecal-perineal-urethral route
- Urinary tract infection (women) caused by incorrect wiping technique (back to front when it should be front to back)
• Poor dental hygiene/dental work
- Common cause of harmless bacteraemia
- Dental extraction
- Gingivitis
- Brushing/Flossing
Flora in mouth would get access to blood stream
⇒ Serious infections in high-risk patients (e.g. those without spleen, patients with damaged or prosthetic valves)
2) Normal flora overgrows and becomes pathogenic when host becomes immuno-compromised • Diabetes • AIDS • Malignant diseases • Chemotherapy (mucositis)
When normal flora is depleted by antibiotics
• Intestine -> severe colitis (Clostridium difficile) • Vagina -> thrush (Candida albicans)
Why are patients with no spleen highly susceptible to blood-borne infections?
?
Why should Antibiotic prophylaxis be given to those without a spleen?
?
What are the second lines of defence?
Phagocytes
Chemicals
That lead to inflammation
These factors will contain and clear the infection
How would taking anti-acids for a stomach ulcer lead to food poisoning?
Anti-acids alter and increase the acidic pH of the stomach.
This is bad because the acidic environment prevents bacterial growth in the stomach and colonisation in the intestines.
Why would eczema, dermatitis or insect bites cause cellulitis?
Cellulitis is an infection of soft tissue on the skin so any condition that affects the skin integrity
What are the three main phagocytos and what are their functions?
Macrophages:
- Present in all organs
- Ingest and destroy microbes (Phagocytosis)
- Present microbial antigens to T cells (adaptive immunity)
- Produce cytokines/chemokines
Monocytes:
- present in blood
- recruited at site of infection and then differentiate to macrophages
Neutrophils
- present in blood
- look for it in full blood count because it’s increased during infection
- Recruited by chemokines to the site of infection
- Unlike macrophages, neutrophils die, they are the major WBC component of pus
- Ingest and destroy pyogenic bacteria: Staph. aureus and Strep. pyogenes
What are the functions of basophils/mast cells?
Early actors of inflammation (vasomodulation)
Important in allergic responses
What is the function of eosinophils?
Defence against multi-cellular parasites (worms)
What is the function of NKCs?
Kill all abnormal host cells (virus infected or malignant)
