Fundamentals I: 11:00 - 12:00 Scribe: Melissa Precise
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Tuesday, September 28, 2009 Proof: Matthew Davis
Dr. Barnum Cytokines Page of 8
I. Cytokines [S1]:
a. This morning going to talk about cytokines!
i. These are molecules that are involved in regulating all aspects of the immune system in terms of development and immune responses.
II. Inflammatory Response Figure [S2]
a. This is actually an outdated overview.
b. The light blue letter combinations/ number combinations are all the cytokines that regulate different aspects of immune response
i. Start from stem cells to generation of all effector types of cells
ii. Activation of T cells and B cells and everything.
c. Know now that there are at least a hundred different cytokines. This is an extremely complex field that will only touch on few points that are relevant in terms of:
i. How the immune system develops
ii. How cytokines are involved in the activation of lymphocyte development
iii. How cytokines fight off bacterial and viral infections
d. Will go over these aspects of cytokines to know what is going on.
III. Cytokines Are Important Because: [S3]
a. Cytokines are master regulators of immune system from the get-go
i. From stem cells to all the different progenitors to the trafficking of those cells that get in and populate secondary lymphoid organs like lymphnoids and the spleen.
b. Cytokines and hemokines are involved in that kind of movement.
c. Initiation of immune responses, activation of cell types involved, and ultimately the resolution of the immune response to the invading pathogen are all in part controlled by different cytokines.
d. This makes important for you because cytokines are now used as therapeutic reagents.
i. Will encounter patients that are being treated with cytokines for one reason or another
1. May be undergoing chemotherapy, so white cell counts and red cell counts are down
a. May need cytokine treatment to get cell count up so can survive next round of therapy
2. May have an auto-immune disease
a. Many types of antibodies that target specific cytokines that are used to control specific auto-immune diseases
ii. Use of cytokine treatment will only increase over time as figure out more about these molecules and take advantage of things they can do.
1. May encounter patients that are being treated with cytokines. May be prescribing these in the future – never know!
IV. Cytokine Nomenclature [S4]
a. Like a lot of things in the immune system, Cytokine nomenclature is a real mess.
i. As times goes on, we understand more about the field and what is going on, so we get a better idea of what the molecules are doing.
b. When people were first naming these molecules, the molecules were characterized based on types of assaying used at the time.
i. Monokines – cytokines only thought to be produced by monocytes
1. Now know cytokines are produced by a lot of other cell types – not a term likely to encounter
ii. Lymphokines – thought to be only produced by activated T cells and now know this is not always the case – but term is still used
iii. Interleukins – cytokines produced by leukocytes which acted only on leukocytes
1. Not true either, but interleukin nomenclature is the most common nomenclature for cytokines now
c. When in college, the interleukins interest was IL-1 and IL-2. Now up to IL-37 or IL-38. So continually finding more and more of these molecules which do a lot of things in immune response.
d. Interferons – cytokines very critical for controlling viral infections
i. Without these, going to have a rough time handling viral infection
ii. Will talk more about these and how they contain viral infections
e. Colony-Stimulating Factor – help development of the effector cells in the immune system, so help in development and maturation of leukocytes and neutrophils in the immune system – very common to see
i. Some are used therapeutically
f. Chemokines – large family
i. Important in traction and movement of cells
ii. Important in movement of cells in and out of the lymph nodes
1. Will see how important – even when do not have infection present
g. Growth factors – involved in stem cell differentiation and a number of other functions
h. Big nomenclature for all the cytokines
i. Important cytokines are interleukins, interferons, and Colony Stimulating Factors – will be what come across in literature and textbook
V. Cytokine Functions Are: [S5]
a. Cytokines are complex
b. Pleiotropic – mediate many overlapping functions
i. Cytokines regulate T cell development and can also be involved in acute phase response.
1. Cytokines can all mediate different functions based mainly on the expression of the appropriate receptor for them to bind to.
2. After binding to the receptor, they will then stimulate that appropriate cell
ii. Having multiple functions helps reduce the number of cytokines needed to control an immune response because have lots of different cytokines that can mediate different signals. The sum of that signal will help determine what the T cell or B cell is doing.
iii. Lots of different cytokines have overlapping functions.
c. Redundant – many of the functions are redundant
i. An example is TNF-a which mediates the same functions as an IL-1 and IL-6.
1. This enables all three to work together to mediate some of the functions.
d. Synergism – ability of cytokines to really pump up a response
i. Looking at response of an immune protein.
1. Treat the cell with IL-1 and get response
2. Then treat cell with IL-6 and get same response
3. If put these two together, will not get a response that is additive, but will get a response that is much more. (Drew graph on board explaining).
a. So molecule can work together to really turn up immune response and control the invading pathogen.
e. Antagonistic – have to resolve the immune response or will have trouble
i. Do this with cytokines that are antagonistic
ii. Examples are INF-g(pro-inflammatory) and IL-4(anti-inflammatory)
iii. There are many pairs of antagonistic cytokines present in immune response
f. Student Question: Could not hear question.
i. Answer: Pleiotropic is a cytokine that is going to mediate an effect that may work on T cells, monocytes, basophils, and many others. In each case, the cytokine is going to medaiate a different effect on that cell type because of all the different signals that the cell type is going to get. Redundant type is going to have same response on hepatocytes (liver cells) as on other cells and will turn up the immune response the same way as in another cell type. Will also work under the same circumstances.
VI. Cytokine Properties [S6]
a. Cytokines are low molecular weight proteins or glycoproteins
b. Can be monomers, dimers, or trimers
c. Can be synthesized in active form so ready to go bind to a receptor on specific cell type that it is suppose to mediate.
d. Can be synthesized in inactive form (ex. TGF-b) which when synthesized sits on the cell that made it. Has to be cleaved by an enzyme in order to be able to mediate its function and be active.
e. Cytokines are produced in very low amounts. Secretion is brief and very self-limiting
i. Brief – minutes to hours
ii. Want this because very potent, so do not want in large amounts around body.
1. Large amounts would mess up the resolution of the immune response
2. High levels of some of the cytokines are toxic
a. Some conditions where get too much cytokines in blood known as septicemia or toxic shock syndrome – can be fatal
iii. Active at very low concentrations (10-9 and 10-12 Molar)
1. Does not take a lot to mediate an effect
2. Receptors must have high affinity for these molecules
3. For cytokine to do anything, has to signal by binding to specific receptors on target cell
a. So if have cells that do not have receptor and pour all of those in with the signal, then will not see anything occur because immune response is a receptor mediate event
VII. Cytokine Receptors [S7]
a. Each cytokine has a receptor, but some cytokines are promiscuous and can bind to more than one receptor – but this is not common.
i. Does happen – particularly in the chemikine family (will have different cytokines bind to different receptors)
b. Lots of different family receptor families – at least five different main families
c. Cytokine receptors can be multimeric
i. Have cytokine receptors that have a single monomeric chain or can have two or three polypeptide chains
ii. Very common for cytokine receptors to share some of their subunits
1. IL-12, IL_23, IL-7, and IL-9 all share common subunits.
a. Will discuss later why important
d. Once cytokine binds receptor, sets in motion a series of signal transduction events that we are just going to touch on as an example. Not going to make memorize all signaling pathways.
e. Critical for cytokine mediated function
f. Also critical for therapeutic target drugs used to block signaling pathways utilized by certain cytokines. Becoming a more common theme in a variety of therapeutic settings.
VIII. Figures of Cytokine Receptors [S8]
a. Different families of cytokines
i. This is the only thing really want to know – do not want to memorize structures or all the different pieces of them
b. Wants us to know that each of the different family members have unique structural features.
i. IL-1 binds to receptor made up of immunoglobin domains. Dr. Burrows talked about T cells, T cell receptors, and antibodies. He talked about how they are composed with immunoglobin domains.
1. Immunoglobin domains is a common protein motif used throughout the immune domain that is not exclusive to antibodies or T cell receptors
c. Many of these different families have conserved cysteine residues (which can see in Class I cytokine receptors or for interferon receptors or for TFN-a family receptors)
d. Chemokine receptors are known as seven trans-membrane spanning proteins because they pass through the membrane seven times. Do a lot of signaling through G—protein coupled complexes.
i. Not all chemokines use this, but many of them do
ii. Common motif that they use for signaling.
e. Don’t memorize the structure or all of the different features between these families.
IX. Cytokine Receptor Subfamilies (Figure 29.36) [S9]
a. Some of the cytokines use or share some of their subunits.
i. This is a good example of a family that does this.
1. IL-7 have a cognate receptor subunit (part of cytokine receptor that binds cytokine initially)
2. Also has a signaling receptor subunit which is the gamma chain that is associated with the IL-7 receptor
a. So it is the gamma chain that is mediating the transduction signal into the cell once the binding of IL-7 to the IL-7 receptor has occurred.
i. This complex can then signal into the cell through the gamma chain.
b. If deficient in gamma chain, then will have problem in immune responses because gamma chain is used by IL-9, IL-4, and IL-2 in order to mediate signal. All of these different cytokines are important in adaptive responses, so if do not have these then not going to make T cells or B cells. If do not make these, then immune system will not work and will be in trouble.
i. Do have cases in which have this deficiency – not that common
c. So signaling subunits are critical for mediating intracellular events that occur in immune response.
X. Generalized Cytokine Signaling Mechanism [S10]
a. Example of how cytokines can signal
b. Alpha chains cognate receptor part of the receptor is going to bind to the cytokine.
c. Beta chain signaling receptor will bind and have spontaneous association intracellularly which is done by Janus Kinases.
i. Janus Kinases are a family of kinases that phosphorylates really well.
1. Will phosphorylate intracellular portion of cytokine receptor and creates a docking site for another of family of signaling molecules (STATS).
2. STATS then bind to the docking site on the cytokine receptor intracellularly
3. Once docks, will become phosphorylated by Janus Kinases as well and will then dimerize
4. Dimer of STATS molecule will translocate into nucleus and will serve as a regulatory molecule of transcription factor for certain genes that are mediated by that certain cytokine
d. RECAP: Cytokine binds to receptor and the cytokine receptor is phosphorylated by Janus Kinases forming a docking site for the STATS and once they are phosphorylated by Janus Kinases they are translocated into the cell so can turn on immune response.
e. Lots of different pathways for STATS which regulate all of the different genes that cytokines regulate
f. This is a generalized example of how system works.
g. There was a student question but cannot distinguish on audio.
XI. Cytokine Effects on Target Cells are: [S11]
a. Cytokines can act in several different ways
b. Autocrine – act on the cell that produced it
i. Ex. IL-2 is very potent cytokine regulating T cell activation.
ii. Early on when T cells are becoming activated, they need a number of cells to be activated. Will start to produce IL-2 which binds to IL-2 receptor. This is one of the ways to get the T cell activated and going.
c. Paracrine – acting on cells close by
i. Ex. Interferons – IFN
ii. Interferons are made when cells realize they are virally infected. Interferons will bind to cells nearby and turn on to help protect them against viral infections
d. Endocrine –
i. Levels of cytoknie can reach high enough levels that get into bloodstream – in this setting the cytokine can act as a hormone.
ii. Ex. TNF or IL-1 which are important in development of fever when have a bacterial infection for example. Will reach high enough levels in bloodstream, so can travel to brain and bind to appropriate cells that regulate thermal regulation in the body.