MCB Lecture 42 Innate Immune System Flashcards
What are the two types of molecules that can be detected on microbes?
PAMPs: molecules conserved in microorganisms. Not unique, but rather found in many taxonomical groups eg. LSP
Antigens: molecules on a microorganism that are particular to that particular species. Eg. Haemoglutinin and Neurominadase on influenza virus
Why have an immune system?
To protect the individual against invading microorganisms
Which receptor recognises PAMPs?
PAMP recognition receptor
PRR
Which receptor recognises antigens?
Antigen receptor
Antibody
What are the requirements of the innate immune system? (4)
- Rapid
- Present at birth
- Appropriate for pathogen
- Distinguish self from non self
What are opportunistic infections?
These are microorganisms that only cause harm when given the opportunity; opportunistic invaders
Describe how and when the immune system evolved
It enveloped due to pressure from microorgansism a that were invading and causing harm
The innate immune system evolved first
The adaptive immune system evolved when some pathogens escaped the innate immune system
What are the characteristics of the innate immune system? (5)
- Fast response
- The magnitude is constant
- First line of defence
- Non specific
- Interacts and educated the adaptive response
What are the components of the innate immune system?
Barriers, secretions, cells
Describe how epithelium is part of the immune system
These form a physical barrier to prevent microorganisms getting into the host Eg. Epithelium of trachea and lungs Skin epithelium Gut epithelium Nasal epithelium
Describe how secretions form part of the immune system
These are secreted by epithelium, and prevent microorganisms from getting in, or killing them
Eg.
Mucous secreted by trachea epithelium
Lysosyme and Phospholipase A in the mouth and tears
Gastric juice: acidic to kill the pathogen
Bile salts
Where is lysosyme found?
In the mouth and in tears
Where is Phospholipase A found?
What does it do?
In the mouth and in tears
It disrupts the cell membrane of bacteria and other pathogens
Describe how normal flora protect us in the immune response
Commensals are found on many outer surfaces of the body
They take up space so that other bacteria which are harmful cannot take up residence
They prime out innate immune system
Eg. On skin In throat In the gut Vagina
What are plasma factors ? (3)
- C reactive proteins
- Mannose binding lectin
- Complement proteins
Describe the function of C reactive protein
These coat microbes and trigger phagocytosis and the complement cascade
What is mannose binding lectin?
It is a protein that binds to mannose on the surface of a bacterium.
It triggers the complement cascade
What is a lectin?
It is a protein that binds to a sugar
Give a brief description of the complement system
Activated via one of three pathways
Critical step: C3 is cleaved
Outcomes: microbe is phagocytosed, lysed and phagocytes and inflammatory cells are attracted
How can the complement system be activated?
- Classical pathway: antibody binds. C1 -> C2 -> C4
- Lectin pathway: lectin binds to mannam.
- Alternate pathway: binding to molecules on the surface of the pathogen
What is the critical step in the complement system?
Cleavage of the C3 protein
What does proteolysis of the complement proteins bring about?
It brings about the evolution of other cleavage products
These bind to the surface of pathogens and bring about the outcomes
What are the outcomes of the complement system?
- Opsonisation : C3b coats a pathogen, and phagocytosis is induced
- Lysis: C5,6,7,8,9 come together to form a pore in the cell wall of the microbe. The cell lyses and dies
- Chemotaxis: C3,4,5a attract phagocytes and inflammatory cells
Describe the process of opsonisation
How is it activated?
C3b coats a microbe, and phagocytosis is induced
It is activated by the cleavage of C3, ie the complement system
