Innate immunity Flashcards
What are some examples of chemical barriers to infection?
- Acid in the stomach
- Mucus on the surface
- antimicrobial properties e.g defensins which are secreted at the epithelial surface
What is the function of the innate barriers of infection
To prevent pathogens from gaining access to the deep tissues
What do epithelial layers produce?
They produce protective substances
* acidic pH
* enzymes and binding proteins
* antimicrobial peptides
What are sentinel cells?
Resident tissue cells that detect invasion by recognising DAMPS and PAMPS
they can then send signals to initiate a response to
* dendritic cells
* Macrophages
* Mast Cells
*
What kind of cells develop from myeloid progenitor cells?
- Red blood cells
- Monocytes
- Megakaryocytes
- Granulocytes
What kidn of cells develop from lymphoid progenitor cells
- T cells
- B cells
What is the precurser to macrophages and dendritic cells?
Monocytes
What is the function of dendritic cells?
Important bridge between innate and adaptive immunity
can act as APC’s
What kind of cells do NK cells kill?
any virus infected or abnormal cell that fails to express MHC Class I molecules
What kind of cells are MHC I molecules usually present on?
all nucleated cells of the body
What do MHC class I receptors do when they bind to NK cells?
switch off their ‘killing abilities’
What is the definition of phagocytosis?
engulfment and internalisation of materials such as microbes for their clearance and destruction
What are the two different receptors that are found on phagocytes (recognise microbes)
- Pattern recognition receptors- bind to the LPS of bacteria
- Opsonin receptors, e.g immunoglobulin FC receptors- bind to iG + AG
What is the definition of the complement system?
A group of serum proteins circulating in inactive form
What systems activate the complement system?
Both the adaptive (classical pathway) and the innate immune system ( alternative pathway)
What are the possible outcomes after the complement system is activated?
- Targets cell lysis
- Chemotaxis
- Opsonisation to enhance phagocytosis
What are the three activation pathways that are part of the complement system?
- Classical
- Lectin
- Alternative
What is the classical activation pathway
requires the interaction of an antibody with a specific antigen
What is the lectin activation pathway?
PAMPS recognition by lectin receptors
What is the alternative activation pathway?
activation of the complement via the microbe itself
What is the function of cytokines?
- coordinate an effective immune response
- Moderate the communication between lymphocytes, inflammatory cells
and haematopoietic cells. - additional roles separate from the immune system in developmental
processes such as - cell differentiation
- directed migration.
Influencing both innate and adaptive immune responses
What are some of the different families of cytokines?
- Pro-inflammatory cytokines
- Chemokines
- Inteferons
Where do defensins sit?
They sit in the lipid bilayer
What two cells are examples of monocytes?
Macrophages and dendritic cells
How many populations of innate lymphoid cells are there?
at least four
* ILC1- found in large numbers in the intestinal wall
* ILC2- scattered throughout the body and secrete cytokines
* ILC3- act like TH17 cells and promote inflammation by releasing TH17
* ILC4 natural killer cells
How do defensins work?
They can directly kill or inhibit the growth of microorganisms
What are the two phagocytic cells?
Neutrophils and Macrophages
What are the innate lymphoid cells?
- Cytokine secreting ILC’s
- Cytotoxic ILC-NK cells
How do the leukocytes get where they are required?
- Macrophages produces cytokines such as TNF-alpha and IL-1
- TNF-alpha, IL1 and other chemokines activate selectins
- The force of blood flow causes leukocytes to roll
- Chemokines produced in the surrounding tissues bind to the rolling leukocytes in a high affinity state
- Leukocytes can crawl to junctions and migrate through the wall (diapedesis)
What are the functions of the natural killer cells?
- They can kill virus-infected or other ‘abnormal’ cells that fail to express MHC class I molecules
- If MHC I binds to a natural killer cell it ‘switches off’ the killing abilities
What happens when certain viruses and tumours ‘down regulate’ the expression of the MHC class I molecules?
The natural killer cells bind to the virus-infected target cells, inject them with proteins to induce cell death and thus eliminate the virus-infected cells
Give some examples of antimicrobial phagocytic mechanisms
- Toxic Nitrogen oxides- NO
- Enzymes- Lysozyme (digests the cell wall of gram-positve bacteria)
- Antimicrobial peptides- Cathelicidin in macrophages, defensins in neutrophils
How does the classical pathway begin?
Antibodies binding to antigens, Cleavage of C1 causes a cascade of other proteins becioming activated
How does the alternative pathway begin?
With the spontaneous hydrolysis of C3
What are pro-inflammatory cytokines?
IL1, IL6, TNF
Secreted by sentinel cells in response to DAMPS and PAMPS
Causes fever, lethargy, loss of appetite
What kind of cells produce interferons?
- Produced by virally infected cells, within 24 hours of some infections
What kind of cells can produce chemokines?
Sentinel Cells
