Cytokines II Flashcards
Exam 2
What is the role of CXCL8 and how are neutrophils targeted to the right place to penetrate the endothelium and then recruited to the infected tissue?
At the site of infection, activated immune cells are recruited as a part of innate immunity. The infection activates tissue resident macrophages to release cytokines, which recruit other cells to the area.
Prominent cytokines in pro-inflammation: IL-1Beta, TNF-alpha, IL-6, CXCL8 (a chemokine), IL-12
What is the purpose of the various protein-protein interactions involved in this targeting at the endothelium?
Protein-protein interactions are vital in the contect of cell adhesions (adhesion of leukocytes to the endothelial cells), signal transduction (protein interactions activate signaling pathways, and immune responses.
What are the types of biological roles of various cytokines in the process?
At the site of infection, resident macrophages secrete inflammatory cytokines, such as…
IL-1Beta and TNF-alpha–> Induce blood vessels to become more permeable, enabling effector cells and fluid containing soluble effector molecules to enter the infected tissue.
IL-6–> Induces fat and muscle cells to metabolize, making heat and raising temperatures in the infected tissue
CXCL8–> Recruits neutrophils from the blood and guides them to the infected tissue
IL-12–> Recruits and activates NK cells that in turn secrete cytokines that strengthen the macrophages response to infection.
List the diverse structural characteristics of the cytokine receptor types (different numbers of
chains, domains, adaptor proteins, etc)
TNF receptor family
* Common cytokines: TNF-alpha, CD40, April, Nerve growth factor, TNF-Beta, FastL, Ox40, LT, BAFF, GITR
* Structural Characeristics: exist as membrane anchored and soluble forms, released by lymphocytes and monocytes along with IL-1, IL-6, and interferon gamma, when infection is detected. Receptors include the cys rich domains, TNFR1, and TNFR2 domains. Target cells–> TNFR1 constitutively expressed on most cell types; pro-inflammatory and apoptotic—> TNFR2 restricted to endothelial, epithelial, and some immune cells; anti-inflammatory and promotes cell proliferation. Can induce fever, apoptosis, and inflammation.
Type I and II (hemopoietin) receptors
* Common cytokines: IL-1, IL-5, IL-9, !L-13, GM-CSF, IL-3, IL-6, IL-11, IL-15, G-CSF, IL-4, IL-7, IL-12
IL-1 receptor family
* Common cytokines: IL-1, IL-18
IL-17 receptor family
* Common cytokines: IL-17
Why does TNFalpha have opposing outcomes for different cell types (i.e. pleiotropism of ligands)?
- Receptors: cys-rich domains; TNFR1, and TNFR2
- TNFalpha binding leads to receptor oligomerization and changes in intracellular protein-protein interactioons to generate the active complex of multiple proteins.
- Activates NF-kB or MAPK pathways and specific gene expression
- Signaling effects are complicated often conflicting
What are the TNF receptors activated by TNFalpha?
TNFR1 and TNFR2 are both activated when TNFalpha binds to the receptor, leading to oligomerization.
What is receptor cross-reactivity and receptor common chains? How do these two features of cytokine receptors explain redundancy of cytokines?
- Sharing a subunit explains certain cytokine redundancy.
- Cytokine binds to alpha subunit
- The complex associates with a common beta subunit (in cross reactvity, and they become high-affinity receptors.
- The signal is transduced through the beta subunit (redundancy).
What is receptor oligomerization and how does it trigger signaling?
Receptor oligomerization refers to the process by which individual receptor molecules, often of the same or different types, come together to form larger complexes/oligomers. In the case of GPCRs, receptor oligomerization often enhances the ability of the receptor to activate the associated G proteins. Oligmerization can faciliate the generation of second messengers by recruiting enzymes like phospholpases or kinases to the oligomerized receptor complex, which increase downstream signaling cascades.
What is the JAK/STAT pathway of type I and II receptors? What kind of proteins are JAK and STAT?
JAK/STAT pathway overview
* Many type I and II cytokine receptors signal through this pathway, e.g. IL-6, IFN-gamma
* JAK kinase associated with the receptor
Steps:
1. Cytokine binding dimerizes receptor, making a pair of JAK kinases
2. JAK is activated, phosphorylates receptor
3. STAT docks and is phosphorylated
4. pSTAT dissociates and pSTAT dimerizes
5. pSTAT dimer translocates to nucleus and mediates transcription of specific target gene in a cell type.
What kind of proteins are JAK and STAT?
* Janus Kinase–> JAKs are a family of intracellular tyrosine kinases
* STAT–> transcription factors that belong in a family of proteins
How are cytokines linked to disease and to drug action?
Example of IL-6 and IL-6 receptor
Example of IL-17 receptors activation by IL-17
How do drugs, mostly antibodies, that are directed against cytokine/cytokine-receptor interactions work?
TNF-alpha
* Has a role in disease of cancer and autoimmunity.
* Dysregulation impacted in Alzheimer’s, depression, IBD
* Tasonermin: TNFalpha used as immunostimulant drug to treat certain types of cancers
* Etanercept: approved to treat rheumatoid arthritis, psoriasis. This works by a fusion protein being produced by recombinant DNA; extracellular TNFR2 is fused to Fc region of an IGG1 antibody. It acts to suppress TNFalpha signaling by binding TNFalpha (like a decoy receptor), thereby interfereing with its physiologiical functions. The IgG1 Fc extends the lifetime in the bloodstream.
IL-6 in diseases
* IL-6 (alongside IL-1Beta and TNFalpha) are powerful proinflammatory cytokines with a wide range of biological effects on different organs
* IL-6 dysregulation contributes to inflammatory and auto-immune processes in many disease (ex. rheumatoid arthritis, multiple scelerosis, lupus, prostate cancer, myeloma
* Cancer: IL-6 has a role in chronic inflammation and in regulating tumor microenvironments and metastasis
* Enterovirus 71: highly contagious; causes the mild illness hand/foot/mouth disease, but also encephalitis to which IL-6 contributes
Drugs against IL-6
* Development of anti-IL-6 agents is progressing
* Siltuximab: antibody agains IL-6–> approved to treat Castleman disease (lympho-proliferate disorder)
* Toxilizumab and Sarilumab: antibodies against soluble and membrane bound forms of IL-6R–> approved to treat rheumatoid arthritis.
IL-17
* Discovered in 1993 from a rodent T-cell hybridoma
* Secreted as homodimer and heterodimer of IL17-A/IL17-F from several immune cells, including activated T cells
* Several target cells including macrophages, T cells, endothelial cells, fibroblasts
* IL-17 receptors are a heterotrimer of IL-17RA/IL-17RC
* Signaling pathway involves ACT1 (adaptor protein) association with intracelular receptor regions and series of kinases, promoting expression of pro-inflammatory cytokines, chemokines, and anti-microbial peptides.
* Biological effects: primarily pro-inflammatory immune responses–> beneficial against infection from bacteria and fungi–> BUT detrimental when highly expressed in chronic inflammatory diseases like asthma and COPD. Dampens anti-tumor immunity
* Secukinumab: antibody against IL-17A has FDA approval against psoriasis.
Cytokine-based therapeutics
* Cytokine antagonists–> antibody biologics targeting pro-inflammatory cytokines or receptor have clinical success–> functions by blocking the pro-inflammatory function of TNFalpha, IL-6, IL-17, and IL-23, treating autoimmune disease–> Outcome? Patient dependent on the drug. Complications with multiple disease like IBD or MS. Disease stage is a factor, possibly incease the risk of cancer and infections—> need to continue to research (pleotropism)
* Recombinant cytokines–> engineered cytokines as therapeutics–> Type 1 interferons to treat viral disease (hepatitis)–> IL-2 promotes T cell growth and has considerable antitumor immue response in melanomas, but less than 10% of patients respond and can have severe adverse effects, including death–> Problems? Low bioavailibility and pleiotropism–> Need to develop modified cytokine variants that are more selective
What does dysregulation lead to in the immune response?
- Recurrent infections and impaired wound healing as seen in immunodeficiencies
- Excessive inflamation, as in chronic inflammatory disease
- Abnormal proliferation and apoptosis, as in cancer
What are the roles of cytokine signaling pathways in immunology?
- Macrophage release of chemokines induces leukocyte migration
- Stimulate B cell development and gene recombination to produce antibodies
- Stimulate blood cell differentiation
- T cell activation
- Triggers cell proliferation
- Wound healing
The expression of cytokine and cytokine receptors is highly regulated to control both pro-inflammatory and anti-inflammatory responses.
Describe how the macrophage release of cytokines induces neutrophil migration.
- Neutrophil circulation in the absence of infection
* Selectin: glycoproteins that exhinit weak reversible binding to sialyl-Lewis X carbohydrates on passing neutrophils in the blood stream–> rolling adhesion - Neutrophils are the first wave of cells recruited to the site of infection
* Recruitment is mediated by the cell-adhesion molecule ICAM-1, an immunoglobulin-like protein; ICAM-1 expression is induced locally by TNFalpha; it initiates tight binding to an LFA-1 integrin on neutrophils; neutrophil can now cross the endothelium–> diapedesis
* CXCL8 (chemokine) is secreted by macrophages; directs neutrophils where to cross the endothelium and subsequent migration to the infected tissue by moving along a concentration gradient of CXCL8. - Similar process occurs with monocytes (pre-macrophage) in the bloodstream, which is recruited by CCL2.
Characterize type I receptors
They have multiple receptor chains, but several cytokines engage a common chain.
Examples:
* IL-15 and IL-4 have a common gamma chain
* GM-CSF and IL-5 have a common Beta chain
* IL-6 and IL-11 have a common gp130 chain
What are the common characteristics of IL-6?
- IL-6 is pro-inflammatory cytokine primarily secreted by T cells.
- It is important for T-cell differentiation and proliferation
- Also, differentiation of B cells into plasma cells
