L#17 & #18: Leukocyte Adhesion, Activation, and Migration and Cytokines.
L#17 & #18: Leukocyte Adhesion, Activation, and Migration and Cytokines. 0530
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This 4 page Class Notes was uploaded by Denise Croote on Saturday January 23, 2016. The Class Notes belongs to 0530 at Brown University taught by Dr. Richard Bungiro in Fall 2013. Since its upload, it has received 28 views. For similar materials see Principles of Immunology in Biology at Brown University.
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Date Created: 01/23/16
Lecture Seventeen: Leukocyte Adhesion, Activation, and Migration The Inflammatory Response: o Signs: Heat, Redness, Swelling, Pain, Loss of Function o Damaged tissues release histamines, increasing blood flow to the area o Histamines cause capillaries to leak, releasing phagocytes and clotting factors into the wound o Phagocytes engulf bacteria, dead cells, and cellular debris o Platelets move out of the capillaries to seal the wound o T cells and B cells do NOT mediate inflammation – NEUTROPHILS are responsible for mediating inflammation When you get injured, your granulocytes recognize that you are injured and they travel to the site of the injury You produces 2 X 10 neutrophils every day because neutrophils have a very short lifespan Neutrophils are very distinct looking because of their globular blobs inside Neutrophils main job is to phagocytosis and kill invading bacteria T cells and Neutrophils are both circulating in the blood stream. The T cells will leave and enter the lymph and the neutrophils will leave and enter the injured area. Extravasation is a stepwise process that involves cells leaving the blood stream o First cells adhere to the endothelial walls o Second chemotaxis causes direction movement up a chemical gradient Neutrophils and T cells know to adhere in the correct places because they have specific adhesion and chemotactic receptors T cells circulate to increase the likelihood that they come in contact with an Antigen This is a surveillance function. T cells will sample the antigens being presented by DC cells in the lymph nodes and spleen and will be selected for it they bind to the DC and antigen At the site of an injury the injured skin release cytokines and this activates the endothelial layer near the site of an injury o Neutrophils will be circulating in the blood stream and will notice that the endothelial layer near the injured site is sticky o They will adhere to the wall and start the process of Rolling Activation Arrest/Adhesion Transendothelial Migration o They must do all this without damaging the endothelial layer because if they damage the layer and it becomes leaky, fluid will come in and will cause the area to swell even more o This occurs in T cells as well, but it happens on the wall of the spleen and lymph nodes. These structures have their own special epithelial layer and this layer selectively attracts T cells o Selectins: involved in the rolling phase – they bind sugars and mediate cell to cell interactions. Some selectins are present on endothelial cells, some on leukocytes, and some on platelets Selectins show increased expression during inflammation These receptors slow down the circulating neutrophils so that they can be recognized All endothelial layers are packaged with selectins, they are just resting in the interior until they are called to action and then they are moved to the exterior o Integrins: are also receptors, but are involved in the activation, arrest/adhesion, and transendothelial migration steps Integrins are present on the leukocyte and they bind to the Ig – Superfamily CAM on the endothelium layer When the cell is circulating integrins are in a low affinity state When selectin binding and activation occurs they transition to a high affinity state o Selectin binding is the first step and it is a loose binding, Integrin binding is the second step and it a tight binding (ensures that the neutrophils will not be swept away) o After this process occurs, the endothelial cells bounce back to normal o T cells do not do this at the site of an injury because the endothelial layers that the T cells bind to are a different consistency o Once cells leave the blood stream they go exactly to where the wound occurred and they are able to do so with precision because of chemotaxis Experiment: if you knock out a selectin and a ligand you notice the neutrophils start to accumulate in the blood (accumulation does not occur for any other cell type). This occurs because they are not binding to the endothelial layer If you knock out a selectin you get a lower binding rate, if you knock out a ligand you get a lower binding rate, but if you knock out both you get absolutely NO binding (this implies that other factors are involved because if it was just the ligand and the selectin, knocking out just ONE would eliminate the entire response Experiment: if you knock out MAC1 – which is an Integrin, you do NOT get a neutrophils response Summary: 1.) Capture of the neutrophils by selectins – this is termed rolling a. first one set of selectins bind to the ligands (carbohydrates) on the neutrophil’s surface b. then the sheer force of the circulating blood causes the neutrophils to tumble, breaking the first selectin binding interaction and establishing another a little farther on the cell membrane 2.) Activation by a g protein coupled receptor - this activation is referring to the interaction between the chemokines presented on the surface of the endothelium and the neutrophils. a. The neutrophil has chemokine receptors that respond to the chemokines on the endothelium b. Signal transduction that results from binding elicits a change in conformation c. Change in conformation causes clusters integrins to amount on the neutrophil’s surface 3.) Adhesion of the neutrophils as a result of integrin binding 4.) Transmigration a. either paracellular which is in between endothelial cells b. or transcellular – which is right through an endothelial cell c. leaves the cells unharmed LAD1 = leukocyte adhesion deficiency o Genetic defect in integrin expression o Cannot bind neutrophils so there are a high number of neutrophils in circulation o Neutrophils from patients can roll (because that involves the weak binding of selectins) but they cannot stick o Characteristic bacterial infections o When inflammation occurs neutrophils cannot infiltrate the injury Alpha4B7 and alpha 4B1 are integrins necessary for the inflammatory response o Anti-inflammatory drugs target alphaB1 and attempt to down regulate it so inflammation decreases o Anti-inflammatory drugs can also be designed to prevent the endothelial layer from becoming sticky (so neutrophils aren’t caught) o Anti-inflammatory can also block chemokines so no signaling occurs and neutrophils aren’t attracted to the sites of infection o Chrones Disease and Multiple Sclerosis are results of over inflammation Chemotaxis: Once the neutrophil is inside the injured area, it becomes polarized, is induced to change its cytoskeleton, and has a receptor for the bacteria that it uses to chase the bacteria Certain chemokines attract neutrophils, just as basophils and esonophils are attracted by different chemokines END OF CHAPTER QUESTIONS 1.) Chemokines and chemoattractants are for leukocytes (attracting neutrophils to the site of an infections) but also for lymphocytes 2.) The chemokine receptor CCR7 is initially absent in naïve B cells. This receptor binds to chemokines that guide the cell to the paracortex (so it is initially present in T cells). Once B cells have been activated by an antigen they start to express CCR7 so that they can migrate to the paracortex and interact with T cells 3.) Antigens do not have to be attached to and APC when they enter the lymph nodes, they can enter by themselves (commonly opsonized by a complement protein) through the afferent lymphatic system 4.) One T cells find an antigen on a DC they match, they stop migrating and searching for antigen 5.) An example of chemotaxis during an immune response is when B cells migrate from the follicle to the paracortex to interact with the T cells after they have been activated. Neutrophils responding to an injury is also an example 6.) Leukocyte extravasation occurs by the process of rolling, activation, adhesion, and then transendothelial migration 7.) Chemokine activation is required to change integrins from their low affinity state to their high affinity state so that they can adhere the leukocyte that is rolling on the endothelial layer 8.) Lymphocytes so not enter tissues other than the secondary lymph organs because they have selectin receptors that are specialized for interaction with the lymph node endothelium 9.) T cell and B cell movement is guided by networks and the T and B cells know where to go in the lymph nodes (are compartamentalized) by the presence of chemokine receptors. For example, the T Cell has CCR7 and that guides it to the paracortex 10.) TCR interact with MHC, Chemokines interact with G protein coupled receptors, E selectins interact with L selectins Lecture Eighteen: Cytokines Cytokines are low molecular weight proteins and glycol-proteins that are secreted by other cells to respond to various stimuli They assist in regulating the development of immune effector cells and possess some direct effector functions Interferons interfere with viral replication Interleukins are secreted by leukocytes and promote growth and differentiation o IL1-IL36 and TNF (tumor necrosis factors – can cause cell death) Chemokines are low molecular weight cytokines that affect adhesion, chemotaxis, and activation of leukocytes Major Functions: o Cell growth o Cell death o Cell differentiation o Induce responsiveness to other cells o Induce non-responsiveness to other cells o Induce the secretion of other cytokines Cytokines can act on themselves (autocrine), can act on nearby cells (paracrine), and can act on others at a distance (endocrine) Attributes of Cytokines: o Pleiotropy – they can act on more than one cell type o Redundancy – more than one kind of cytokine can have an effect on a certain cell o Synergy – two or more cytokines can cooperate to have a super effect o Antagonism – may work against o Cascade Induction – the action of one cytokine on a target induces that cell to produce another cytokine which induces a target to produce another cytokine Can measure cytokine production with an ELISA - add the antigen of interest, add the antibody and then add a detection antibody Cytokines act on receptors, which signal to activate genes, which have biological effects A cell knows to respond to a cytokine because normally is expresses a moderate affinity IL 2 receptor, but when activated it expresses a high affinity IL-2 receptor Binding of IL-2 to its receptor signals the T cell to enter the cycle IL-2 induces T cell proliferation IL-2 receptor has a Beta subunit and the beta subunit is common in other IL receptors Activating Class I and Class II MHC – cytokines act on the receptors, activate the JAK family of kinases, the JAK kinases phosphorylate STAT and STAT dimerizes and then enters the nucleus for specific gene transcription Naïve CD4+ cells can develop into Th1 or Th2 cells o Th1 cells develop in the presence of a lot of IL12 and they are important in cell mediated immunity by activating CTLs and NKs o Th2 are important in humoral immunity and they develop in the presence of IL4 and activate Abs The Leishmania Puzzle – different mouse strains have different survival rates to a disease depending on which cytokines predominate in their system o With elevated INFy and IL2 the mouse was able to survive the disease after being infected o With high IL4 and IL10 the mouse died o Injecting IL4 and IL10 into the survivor mouse killed it and injecting IFN and IL2 into the mouse that died allowed it to survive the next time Cytokine Antagonists – act by binding to and inhibiting cytokine receptors or inhibiting the cytokine itself o When produced by the host they are thought to regulate the immune response o When produced by the pathogen they are thought to thwart host recognition o If we can learn how to mimic these antagonizing effects we can we might be able to decrease the activity of INFalpha which would help those with chronic inflammation We have boxed cytokines that we can use to stimulate the hematopoietic system in situations where HP is affected ( like chemotherapy) But these can also be taken advantage of by athletes to increase their performance
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