Jan. 31st (Exam 1) Flashcards
What determines the specificity of TLRs for microbial ligands?
- The number of Leucine Rich Repeat Regions
- The actual amino acid sequence
What do the functional TLRs consist of?
2 TLR proteins that can either be homodimers or heterodimers.
Describe the layout of the TLR4 receptor.
It consists of two TLR 4 proteins that only associate with themselves.
What type of bacteria have LPS?
Gram negative bacteria.
Explain how the TLR4 Receptor and other proteins involved can detect the presence of LPS and initiate the production of cytokines.
- CD14 acts a co-receptor for TLR4 Receptor, by binding LPS that is released by gram negative bacteria, or otherwise.
- MD2 protein associates with the homodimer and form a complex with CD14 with LPS bound.
- Adaptor protein MyD88 binds to the TIR part of the TLR and, through a kinase cascade, releases NFKB from the protein it was bound.
- NFKB is a transcription factor that initiates the transcription of inflammatory cytokines.
What are NLRs?
Nod-Like Receptors (NLRs) are cytoplasmic signalling receptors that recognize the intracellular degradation products of pathogens.
What are NLRs similar in structure to?
Explain how NLRs can indirectly initiate the production of cytokines.
They look like TLRs but they are not membrane bound and instead are intracellular.
- They dimerize with the help of RIPK2 protein present in the cytoplasm and bind to degradation products of pathogens.
- Through a similar kinase cascade to TLR4 Receptor, NFKB is released from the protein that it is binded to.
- NFKB enters the nucleus and acts as a transcription factor for inflammatory cytokines.
What do activated macrophages secrete to recruit other cells?
They release Inflammatory Cytokines at the site of infection.
What do the cytokines IL-1beta and TNF-alpha do?
Induce the blood vessels to become more permeable.
This allows effect cells and the fluid that contains soluble effector molecules to enter the tissue.
What does the IL-6 cytokine do?
Induces the fat and muscle cells to metabolize, creating heat and raising the temperature in the infected tissue.
What does the CXCL8 cytokine do?
What is CXCL8 an example of?
They recruit neutrophils from the blood and guide them to the infected tissue.
Chemokine
What is a chemokine?
A chemokine is a chemoattractant cytokine.
What are the IL-1 family of cytokines responsible for?
What is the most studied one?
What are the subfamilies?
They are responsible for contributing to inflammation.
The most studied is IL-1beta
Subfamilies:
1. IL-1
2. IL-18
3. IL-36
What is the precursor to IL-1beta?
What activates it?
proIL-1beta
The precursor to IL-1beta is activated by active caspase 1 which has a precursor called procaspase 1.
What activates procaspase 1?
the inflammasome
What is the inflammasome?
This is the protein complex that involves NLRP3 procaspase 1 and increases the amount of IL-1beta in the cytoplasm.
Describe the positive feedback mechanism that we see with IL-1beta production.
Macrophages create IL-1beta that is secreted and bind to IL-1R on the surface of other macrophages or the same macrophages.
Through the activation of caspase 1 via cleavage induced by the inflammasome, we get more IL-1beta.
What do the inflammatory cytokines recruit to the site of infection?
Neutrophils.
What is the most abundant WBC?
Neutrophils
What does polymorphonuclear mean?
It means that the nucleus has variable shapes .
Are neutrophils long or short-lived?
They are short lived.
What type of cell is recruited first to the site of an infection?
What does their arrival signify?
Neutrophils
The inflammatory response.
What is CXCL8?
This is a chemokine that is made by activated macrophages, which acts to attract neutrophils
The movement of neutrophils from the blood vessels to the infected tissues is facilitated by what?
Adhesion molecules that are on both the endothelium and the leukocytes.
What are the four types of adhesion molecules?
- Vascular addressin
- Selectin
- Integrin
- Immunoglobulin like molecule
How do cytokines impact neutrophil recruitment and movement?
- Cytokines dilate blood vessels
- Endothelial cells are activated to express selectin.
Explain the interaction between selectins and the sialyl lewis x groups that are present on neutrophils.
The selectins interact with the groups and slow the neutrophils down, allowing them to roll across the endothelium.
Aside from the travel mechanisms of selectin and the sialyl lewis x groups on the neutrophils, describe the diapedesis of neutrophils into the infected tissue.
CXCR1 and CXCR2 on neutrophils bind to CXCL8, enhancing their interactions with endothelial cells. This leads to stronger adhesion between neutrophils and the endothelium through integrins LFA-1 and CR3 binding to ICAM-1 and ICAM-2 on the endothelial cells. Neutrophils then secrete elastase, which degrades the basement membrane, facilitating their passage through the endothelium in a process called diapedesis. Once in the tissue, neutrophils are guided by the CXCL8 gradient, migrating toward the site of infection or inflammation to perform their immune functions.
What is extravasation?
This is the movement of cells or fluid from the blood vessels to the tissues.
Regarding the changes in gene expression of neutrophils as they enter the infected tissue, what happens?
- They become more phagocytic
- They make more CXCL8 to recruit even more neutrophils
Compare the phagocytic activity of neutrophils to macrophages.
Neutrophils can take up a wider range of pathogens and particulates and have more toxic substances in their granules, which macrophages don’t possess.
What are the four types of granules that the neutrophil has?
- Primary (azurophilic)
- Secondary (specific)
- Tertiary (gelatinase)
- Secretory Vesicles
Explain the primary (azurophilic) type of preformed granules of neutrophils.
Contains myeloperoxidase and other enzymes that disrupt and digest the pathogen.
Explain the secondary (specific) type of preformed granules of neutrophils.
Contains lactoferrin protein that competes for valuable metal ions as well as NADPH oxidase that makes ROS.
Explain the tertiary (gelatinase) type of preformed granules of neutrophils.
Contains gelatinase enzyme that restricts the growth of the bacteria by sequestering iron atoms.
Explain the secretory vesicle type of preformed granules of neutrophils.
These contain adhesion molecules that become part of the neutrophils membrane following degranulation - they are important for attachment to the endothelium,
