Infection: The innate immune response Flashcards
What are the general roles of the immune system?
- pathogen recognition
- containing and eliminating the infection
- regulating itself so there is minimum damage to the host
- remembering pathogens to prevent recurrent disease
What are the 4 types of innate barriers that prevent entry and limit growth of pathogens?
Physical barriers
Physiological barriers
Chemical barriers
Biological barriers
Give some examples of physical barriers
- Skin
- Mucous membranes (line every entry to body)
- Bronchial cilia that expel trapped microbes
Give some examples of physiological barriers
- diarrhoea
- vomiting
- coughing
- sneezing
All work to clear the pathogen
Give some examples of chemical barriers
- low pH in skin, stomach, vagina
- IgA in tears, saliva, mucous (binds to microbe to stop it attaching)
- lysozyme
- mucus
Give some examples of biological barriers
- normal flora present in points of entry eg mouth, vagina, skin, GI tract (absent in all internal organs and tissues)
Compete with pathogens, produce antimicrobials and synthesis vitamins eg K and B12
Which patients are at high risk from serious infection from bacteraemia
Asplenic pts at high risk from encapsulated bacteria
Pts with damaged or prosthetic heart valves
Pts with previous infective endocarditis
Give some examples of diseases than can arise when normal flora is depleted by antibiotics
In the intestine: sever colitis with C difficile
In the vagina: thrush from overgrown candida albicans caused by a raise in pH
What are the main types of phagocytes and what is their role?
Macrophages: present in all organs. Phagocytose, present antigens to T cells and produce cytokines.
Monocytes: present in blood. Recruited to infection site where they differentiate into macrophages.
Neutrophils: present in blood. Recruited by chemokines to site of infecrion. Phagocytose pyogenic bacteria - staph aureus and strep pyogenes
What is the function of: Mast cells Eosinophils Natural Killer cells Dendritic cells
Mast cells: allergic responses
Eosinophils: defence against parasites
Natural killer cells: kill abnormal host cells (viral infected or malignant)
Dendritic cells: present antigens to T cells (link innate and adaptive immunity)
How do phagocytes recognise pathogens?
On the pathogen there are Pathogen Associated Molecular Patterns (PAMPs)
These are recognised by Pathogen Recognition Receptors (PRRs) on phagocytes
Opsonins
What is opsonisation?
Antibodies or complement (both known as opsonins) bind to the pathogen and are recognised by the phagocytes as pathogens so can be destroyed
What causes inflammation?
Mast cells recognise PAMPs which causes them to release histamine, this increases vascular permeability and causes vasodilation producing an inflammatory response (rubor, dolor, calor, tumor)
What are the 2 complement pathways?
The complement cascade either:
- causes opsonisation of the pathogen
- destroys the pathogen by rupturing its membrane
