Innate Immunity Flashcards
What is an infectious disease
When the pathogen succeeds in evading and/or overwhelming the hosts immune defences
What is the role of the immune system
○ Pathogenic recognition - cell surface and soluble receptors
§ Determine between self and non self
○ Containing and eliminating the infection - killing and clearance mechanisms
○ Regulating itself - minimum damage to host
○ Remembering pathogens - preventing the disease from recurring
What is the difference between innate and active immunity
• Innate immunity - immediate protection
○ Fast, lack of specificity, lack of memory, no change in intensity
• Adaptive immunity - long lasting protection
○ Slow, specificity, immunologic memory, changes in intensity
○ Can distinguish between gram positive and gram negative, identify specific strings of organisms (90 strings of streptococcus)
List examples of first line of defenses in innate immunity
Physical barriers - skin (mucous membrane, cilia)
Psychological barriers - diarrhoea, vomit, cough, sneeze
Chemical barriers - low pH, antimicrobial molecules
Biological barriers - normal flora
What are the locations and benefits of normal flora
§ Locations include nasopharynx, mouth/throat, skin, GI tract, vagina
§ Absent in blood, internal organs/tissues
§ Benefits - compete with pathogens for attachment sites and resources
□ Produce antimicrobial chemicals
□ Synthesize vitamins
When is flora a problem to the body
§ Can be displaced through breaching the skin integrity, fecal-oral route, fecal-prineal-urethal route (UTI)
□ Poor dental hygiene/dental work - dental extraction, brushing/flossing
§ Serious infections in high risk patients - asplenic (no macrophages that cause IgG antibodies attached to bacteria to be removed from blood), damaged valves
§ Problems occur when normal flora overgrows and becomes pathogenic when host becomes immuno-compromised - diabetes, AIDS, malignant diseases
□ When normal flora is depleted by antibiotics - intestine (severe colitis), vagina (thrush)
What is the difference between first and second line of defense in innate immunity
- First line of defences - limit entry and growth of pathogens at portals of entry
- Second lines of defences - contain and eliminate the infection
Describe the roles of different types of white blood cells
○ Macrophages will sense the microbe - present in all organs, ingest and destroy microbes and presents microbial antigens to T cells (adaptive immunity), produce cytokines/chemokines
§ Monocytes - present in the blood, recruited to site of infection and differentiate into macrophages
§ Neutrophils - present in the blood, increased during infection, ingest and destroy pyogenic bacteria
□ After immune response, must die forming puss
§ Basophils/mast cells - early actors of inflammation, important in allergic response
§ Eosinophil - defence against multi cellular parasites
§ Natural kill cells - kill all abnormal host cells (virus infected or malignant)
§ Dendritic cells - present microbial antigens to T cells (acquired immunity)
Explain how pathogen recognition occurs
§ Pathogen recognition - pathogen associated molecule patterns (PAMPs) associated with pathogens
□ Pathogen recognition receptors (PRRs) on phagocytes (toll like receptors)
□ Receptors at both inside the cells and at cell surface to sense replication occurring within cell
Allows variety of receptors to recognise all bacteria types
Explain how opsonisation of microbes occurs
Coating called opsonise that bind to the microbial surfaces leading to enhance attachment of phagocytes and clearance of microbes
□ When PRR activated, initiate phagocyte activation and produce cytokines to produce inflammation and attract more phagocytes
□ Opsonisation tells phagocyte to begin engulfing
□ Complement proteins C3b, C4b
□ Antibodies IgG, IgM
□ Acute phase proteins - C-reactive protein (CRP), mannose binding lectin (MBL)
□ Essential in clearing encapsulated bacteria - meningococcus, streptococcus pneumoniae, haemophilus influenza b
Explain how phagocytosis occurs
- Chemotaxis and adherence of microbe to phagocyte
- Ingestion of microbe by phagocyte
- Formation of phagosome
- Fusion of phagosome with lysosome to form a phagolysosome
- Digestion of ingested microbe by enzymes
- Formation of residual body containing indigestible material
- Discharge of waste material
What is the oxygen-dependent and oxygen-independent pathway
□ Oxygen-dependent pathway (respiratory burst) - toxic oxygen product for the pathogens such as hydrogen peroxide, hydroxyl radical, nitric oxide, singlet oxygen
□ Oxygen-independent pathways - lysozyme, proteolytic and hydrolytic enzymes
Describe how the complement system occurs in innate immunity
□ Alternative pathways initiated by cell surface microbial constituents (endotoxins or E coli)
□ MBL - initiated when MBL binds to mannose containing residues of proteins found in many microbes
□ C3a, C5a - recruitment of phagocyte
□ C3b- C4b - opsonisation of pathogens
□ C5-C9 - killing of pathogens, membrane attack complex
What is the role of cytokines in innate immunity
Chemo-attraction, phagocyte activation, inflammation
□ Eg. TNF-a, IL-1, IL-6
□ Released by macrophages and attack on liver, bone marrow
□ Have local inflammation actions - vasodilation, vascular permeability, adhesion molecules (attraction of neutrophils)
□ Hypothalamus - increased body temperature
Why are asplenic patients more susceptible to infection
No macrophages that cause IgG antibodies attached to bacteria to be removed from blood
