3 - Innate Immune System Flashcards
What is the definition of the immune system and an infectious disease?
- Immune system = cells and organs that contribute to immune defences against infectious and non-infectious diseases e.g cancer
- Infectious Disease: When a pathogen succeeds in evading or overwhelming the host’s immune defences
What are the main roles of the immune system?
- Recognise pathogen
- Contain infection and eliminate
- Regulate itself to prevent damage to host
- Remember pathogen
What are the differences between the innate and adaptive immunity?
What are the different categories of innate barriers and what is their role?
- Chemical
- Physiological
- Biological
- Physical
PREVENT ENTRY AND LIMIT GROWTH OF PATHOGENS
What are some physical innate barriers?
- Skin
- Mucous membranes with lymphatic tissue
- Bronchial cilia
What are some physiological innate barriers?
- Vomiting
- Diarrhoea
- Coughing
- Sneezing
Expulsion from body
What are some chemical barriers?
- Low pH (skin, vagina, stomach)
- Antimicrobial molecules
What are some antimicrobial molecules in the innate immune response?
- IgA (tears): prevent microbe attaching
- Lysozyme (sebum and urine): punch holes in bacteria
- Mucus
- Beta-defensins
- Gastric acid
What are some biological innate barriers?
Normal non-pathogenic flora in strategic locations such as nasopharynx, mouth, skin, GI
Not present in internal organs or tissues
What are the benefits of having normal flora in the body?
- Immune maturation
- Produce antimicrobial substances
- Synthesise vitamins (K and P)
- Compete with other pathogens
What are some normal flora that inhabit the skin and nasopharynx and what can they cause if displaced?
Why are antibiotics given before dental treatment?
Poor dental hygeine could lead to bacteria getting into the blood stream when dental work takes place and can lead to sepsis
What patients are high risk for developing serious infections?
- Hyposplenic/Asplenic patients
- Patients with damaged or prosthetic heart valves
- Patients with previous infective endocarditis
What is the issue with infections when a patient is immuno-compromised?
Patient has a weaker immune system so can’t prevent overgrowth of normal flora, e.g in diabetes, aids, chemotherapy
What type of cell is needed for adaptive immunity?
- Dendritic cells
What are the key properties of macrophages?
- Present in all organs
- Present antigens to T-cells
- Produce cytokines/chemokines
How are macrophages and neutrophils linked?
The neutrophils reccruited by chemokines to the site of bacteria and they desroy pyogenic bacteria, e.g Staph aureus and strep.pyogenes
How do phagocytes recognise their pathogen?
- PAMPS on pathogens: structures not on host cell, e.g lipids, proteins, nucleic acids
- PRR on phagocytes e.g TLR4
What is opsonisation?
Coating proteins called opsonins that bind to microbial surfaces leading to enhance attachment of phagocytes and clearance of microbes
Used in conjuction with PAMPS
What are some examples of opsonins?
Complement proteins: C3b, C4b
Antibodies: IgG, IgM
Acute phase proteins: CRP, Mannose-binding lectin
What is the process of phagocytosis?
What is the difference between the first and second line of defence in innate immunity?
How is the complement system activated and what are some of the main complement proteins involved in innate immunity?
1. Alternative pathway - initiated by cell surface microbial constituents e.g endotoxins like LPS
2. MBL pathway - when MBL binds to mannose containing residues of proteins on microbes e.g salmonella, neisseria
What do chemokines/cytokines stimulate?
- Phagocytic activation
- Chemotaxis
- Inflammation
(ones in red are macrophage dervied cytokines and the picture is the effects theses have)
Summarise the five steps of the innate immune response.
What are some risk factors for neutropenic sepsis?
- Asplenic/hyposplenic
- Chemotherapy
- Drugs lowering neutrophils, e.g phenytoin
- Chronic granulomatous disease (no respiratory burst)
- Chediak-Higashi syndrome (no phagolysosome)
In general, why are people with chronic granulomatous disease susceptible to large infections?
They lack the enzyme NADPH oxidase, so cannot produce superoxide to destroy bacteria
What is the acute phase response?
Where acute phase proteins are released from the liver in response to cytokines leading to things such as vasodilatation and increased body temperature
What is the function of CRP?
Released by the liver in response to inflammatory cytokines, about 4-6h after injury/inflammation. Rapidly decreases
- Opsonisation of damaged self and pathogens
- Interact with Fc receptors to release inflammatory cytokines
- Activates complement and adaptive immunity
What is the single most important function of CRP?
- Opsonin-mediated phagocytosis
- Binds to phosphocholine on dead or dying cells anf bacteria, promoting phagocytosis
