Lecture 3.2 - Innate Immunity Flashcards
When does an infectious disease occur?
When a pathogen succeeds in either evading or overwhelming the immune defences
What are the 3 major roles of the immune system?
- Recognise pathogen and remembering it for the future
- Containing and eliminating the infection
- Regulate itself ensuring minimal damage to host
What is the aim of the first lines of immune defence?
Preventing entry of the pathogens
What are the 4 major first lines of defence?
- Physical barriers
- Chemical barriers
- Physiological barriers
- Biological barrier
Give an example of a physical barrier
Skin
Give an example of a physiological immune barrier?
Vomiting
What sort of barrier is formed by the low pH of the skin, stomach and vagina?
Chemical barrier
What forms the body’s biological barrier?
The normal flora
In which 3 ways might normal flora allow an infection to take hold?
- Migrating to another site where it is pathogenic
- Overgrowing and becoming pathogenic
- Becoming depleted by antibiotics, allowing pathogens to establish
What are the roles of the normal flora?
Out competing pathogens
Producing antimicrobial chemicals
Synthesising vitamins
What is the aim of the second lines of defence?
Contain and eliminate the infection once the pathogens have breached the first lines of defence
What are the 2 major second lines of defence?
Cells
Chemicals
What is the role of phagocytes?
Recognise and kill microbes
What are the 3 major phagocytes?
Monocytes
Macrophages
Neutrophils
Where are monocytes found?
In the blood - they are recruited to infected tissue where they differentiate to become macrophages
What do macrophages do?
Phagocytosis
Antigen presentation
Production of cytokines and chemokines
Where are neutrophils present?
In the blood - then recruited to site of infection by chemokines
Briefly outline the process of pathogen recognition by phagocytes
Phagocytes all have pathogen-recognition receptors (PRRs), specifically toll-like receptors, which recognise PAMPs on the pathogen. These PAMPs may be carbohydrate, lipid, protein or nucleic acid.
What is opsonisation?
The process whereby proteins called opsonins bind to the surface of a microbe, enhancing attachment of phagocytes.
For which sort of bacteria is opsonisation particularly key?
Bacteria with a thick capsid, e.g. Neisseria meningitidis
Briefly outline the stages of phagocytosis
1) Binding of microbe to phagocyte via PAMP-TLR complex
2) Ingestion of microbe by phagocyte
3) Phagosome, then phagolysosome
4) Microbe digested by enzymes
5) Formation of residual body and waste materials released from cell
By which 2 mechanisms may intracellular killing occur?
Oxygen dependent - respiratory burst
Oxygen independent - lysozyme etc…
Give an example of why phagocytosis might be hindered
Decreased neutrophil number due to chemotherapy
What is the complement system, and how is it activated?
A system of around 20 serum proteins, which is activated either by the MBL pathway or the alternative pathway
What is the role of complement proteins C3a + C5a?
Recruit phagocytes
Which complement proteins are involved in opsonisation?
C3b - C4b
Which complement proteins kill pathogens?
C5 - C9
Give 3 major roles of cytokines/chemokines
- Chemoattraction
- Phagocyte activation
- Inflammation
What is the immune system?
Cells and organs which contribute to the immune defences against infectious and non-infectious conditions
