4. Innate Immunity Flashcards
What is infectivity?
Ability of a microbe to establish itself within and on host
What is virulence?
Capacity of pathogen to do damage in host cell
What is the definition of the immune system?
Cells and organs that contribute to immune defences against infectious and non-infectious conditions (self vs non-self)
What is the most important organ in the immune system?
Spleen
What is the definition of 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
Containing/eliminating the infection
Regulating itself
Remembering pathogens
What is innate immunity?
Natural immunity
Immediate protection
Fast, lack of specificity, lack of memory, no change in intensity
What is adaptive immunity?
Long lasting Slow Specificity Immunological memory - gives stronger and faster immune response Changes in intensity
What are the first lines of defence in the innate immunity?
Physical barriers
Physiological barriers
Chemical barriers
Biological barriers
What are the physical innate barriers?
Skin
Mucous membranes
Bronchial cilia
What are the physiological innate barriers?
Diarrhoea
Vomiting
Coughing
Sneezing
What are the chemical innate barriers?
Low pH
Antimicrobial molecules
What microbial barriers are involved in the chemical barriers?
IgA (tears, salvias mucous membrane) - prevents microbe attaching to host Lysozyme (sebum, perspiration, urine) Mucus - traps microbes Beta-defensins (epithelium) Gastric acid and pepsin
What are the biological barriers?
Normal flora: non pathogenic microbes, strategic locations (nasopharynx, mouth/throat, skin, GI tract, vagina)
What are the benefits of biological barriers?
Compete with pathogens for attachment sites and resources
Produce antimicrobial chemicals
Synthesise vitamins
Immune maturation
What are some example of normal flora that inhabit the skin?
Staphylococcus aureus/epidermidis/pyogenes
Candida albicans
Clostridium perfringens
What are examples of normal flora that inhabit the nasopharynx?
Streptococcus pneumoniae
Neisseria meningitis
Haemophilus species
When do clinical problems start with normal flora?
When normal flora is displaced from its normal location to sterile location Breaching the skin integrity Faecal-oral route Faecal-perineal-urethral route Poor dental hygiene/dental work
Who are the high risk patients for serious infections?
Asplenic and hyposplenic patients
Patients with damaged or prosthetic valves
Patients with previous infective endocarditis
What are macrophages?
Present in all organs
Ingest and destroy microbes (phagocytosis)
Present microbial antigens to T cells
Produce cytokines/chemokines
What are monocytes?
Recruited a infection site and differentiate into macrophages
What are neutrophils?
Increased during infection
Recruited by chemokines to site of infection
Ingest and destroy pyogenic bacteria
What are basophils/mast cells?
Early actors of inflammation (vasomodulation)
Importance in allergic responses
What are eosinophils?
Defence against multi-cellular parasites
What are natural killer cells?
Kill all abnormal host cells
What are dendritic cells?
Present microbial antigens to T cells
What microbial structures are involved in pathogen recognition?
Pathogen-associated molecular pathogens (PAMPs)
- carbohydrates, lipids, proteins, nucleic acids
What are PRRs?
Pathogen recognition receptors on phagocytes
What is opsonisation of microbes?
Coating proteins called opsonins that bind to the microbial surfaces leading to enhanced attachment of phagocytes and clearance of microbes
Give examples of opsonins
Complement proteins: C3b, C4b
Antibodies: IgG, IgM
Active phase proteins: C-reactive protein, MBL
What does the opsonins receptor do?
Signals phagocyte to engulf microbe
Describe the process of phagocytosis
- Chemotaxis and adherence of microbe to phagocyte
- Ingestion of microbe by phagocyte
- Formation of a phagosome
- Fusion of phagosome with a lysosome to form phagolysosome
5 Digestion of ingested microbe by enzymes - Formation of residual body containing indigestible material
- Discharge of waste materials
What are the 2 phagocytes intracellular killing mechanisms?
Oxygen-dependent pathway (respiratory burst)
- toxic O2 products for pathogens
Oxygen-independen pathways
- lysozyme, proteolytic and hydrologic enzymes
What are the 2 activation pathways in the complement system?
Alternative pathway
MBL pathway
When is alternative pathway initiated?
Initiated by cell surface microbial constituents (endotoxins)
When is MBL pathway initiated?
Initiated when MBL binds to mannose containing residues of proteins found on many microbes
What are the antimicrobial actions in the alternative pathway?
C3a and C5a: recruitment of phagocytes
C3b-C4b: opsonisation of pathogens
C5-C9: killing of pathogens, membrane attack complex
What are cytokines and chemokines involved in?
Chemoattraction
Phagocyte activation
Inflammation
What are the clinical problems when phagocytosis is reduced?
Decreased spleen function
Decreased neutrophil number
Decreased neutrophil function
