تدريب Shadowing: Introduction to the immune system - تعلم التحدث بالإنجليزية عبر الفيديو
جارٍ إنشاء الدرس...
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Despite being surrounded by harmful organisms, toxins, and the threat of our own cells turning into tumor cells,
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humans manage to survive, thanks largely to our immune system.
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The immune system is made up of organs, tissues, cells, and molecules that all work together to generate an immune response that protects us from microorganisms,
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removes toxins, and destroys tumor cells.
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Hopefully, though, not all at once.
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The immune response can identify a threat, mount an attack, eliminate a pathogen, and develop mechanisms to remember the offender in case you encounter it again,
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all within 10 days.
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In some cases, like if the pathogen is particularly stubborn, or if the immune system starts attacking something it shouldn't, like your own tissue, it can last much longer,
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for months to years, and that leads to chronic inflammation.
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Your immune system is like the military, with two main branches, the innate immune response and the adaptive immune response.
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The innate immune response includes cells that are nonspecific, meaning that although they distinguish an invader from a human cell, they don't distinguish one invader from another invader.
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The innate response is also feverishly fast, working within minutes to hours.
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Get it?
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Feverishly?
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That's because it's responsible for causing fevers.
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The trade-off for that speed is that there's no memory associated with innate responses.
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In other words, the innate response will respond to the same pathogen in the exact same way, no matter how many times it sees the pathogen.
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The innate immune response includes things that you might not even think of as being part of the immune system.
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Things like chemical barriers, like lysozymes in the tears, and a low pH in the stomach, as well as physical barriers like the epithelium in the skin
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and gut and the cilia that line the airways to keep invaders out.
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In contrast, the adaptive immune response is highly specific for each invader.
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The cells of the adaptive immune response have receptors that differentiate one pathogen from another by their unique parts, called antigens.
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Adaptive immunity is also diverse, meaning it can recognize almost an infinite number of specific antigens and mount a specific response against each of them.
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The trade-off is that the adaptive response relies on cells being primed
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or activated so they can fully differentiate into the right kind of fighter to kill that pathogen, and that can take a few weeks.
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But the great advantage of the adaptive immune response is immunologic memory.
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The cells that are activated in the adaptive immune response undergo clonal expansion, which means that they massively proliferate.
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And each time the adaptive cells see that same pathogen, they massively proliferate again, resulting in a stronger and faster response each time that pathogen comes around.
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Once that pathogen is destroyed, most of the clonally expanded cells die off, and that's called clonal deletion.
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But some of the clonally expanded cells live on as memory cells, and they're ready to expand once more if the pathogen ever resurfaces.
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Now it's time to meet the soldiers, which are the white blood cells or leukocytes.
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Hematopoiesis is the process of forming white blood cells, as well as red blood cells and platelets, and it primarily takes place in the bone marrow.
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Hematopoiesis starts with a multipotent hematopoietic stem cell, which can develop into various cell types.
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Its future is undecided.
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Some become myeloid progenitor cells, whereas others become lymphoid progenitor cells.
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The myeloid progenitor cells develop into myeloid cells which include neutrophils,
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eosinophils, basophils, mast cells, dendritic cells, macrophages, and monocytes,
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all of which are part of the innate immune response
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and can be found in the blood as well as in the tissues.
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The neutrophils, eosinophils, and basophils are considered granulocytes because they contain granules in their cytoplasm.
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And neutrophils, in particular, are also referred to as polymorphonuclear cells, or PMNs, because their nuclei contain multiple lobes instead of being round.
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During an immune response, the bone marrow produces lots of cells, many of which are neutrophils.
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Neutrophils use a process called phagocytosis.
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That's where they get near a pathogen and reach around it with their cytoplasm to swallow it whole, so that it ends up in a phagosome.
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From there, the neutrophils can destroy the pathogen using two methods.
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They can use their cytoplasmic granules or oxidative burst.
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First, the cytoplasmic granules fuse with a phagosome to form the phagolysisome.
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The granules contain molecules that lower the pH of the phagolysisome, making it very acidic, and that kills about 2% of the pathogens.
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Now, the neutrophil doesn't stop there.
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It keeps swallowing up more and more pathogens until it's full of pathogens, and at that point, it unleashes the oxidative burst.
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During an oxidative burst, the neutrophil produces lots of highly reactive oxygen species, like hydrogen peroxide.
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These molecules start to destroy nearby proteins and nucleic acids within the phagolysisomes, which are the components of the pathogen that has been ingested.
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The net result is that the pathogen is eliminated.
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Now, in comparison to neutrophils, eosinophils and basophils are far less common.
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They both contain granules that contain histamine and other pro-inflammatory molecules.
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Eosinophils stain pink with the dye eosin, which is where they get their name.
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They are phagocytic cells, even though it's not their primary mechanism of attack.
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They are best known for fighting large and unwieldy helminthic parasites, or worms, by releasing molecules that can poke holes in the outer layer of helminths.
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These cells are also involved in allergic reactions such as atopic dermatitis and allergic rhinitis, also known as hay fever.
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When involved in allergic reactions, eosinophils degranulate, meaning they release various enzymes and proteins within their granules,
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and this causes an inflammatory reaction.
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Next, you have basophils, and they stain blue with the dihemotoxylin
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and unlike neutrophils basophils are non-phagocytic on the flip side they have granules
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that contain histamine
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and other pro-inflammatory molecules therefore they are important in initiating allergic responses finally there are the mast cells
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which live in tissues not in the blood
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and they're very similar to basophils they are also non-phagocytic and are are involved in allergic responses.
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Next up are the monocytes, macrophages, and dendritic cells, which are also phagocytic cells.
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They gobble up pathogens, present antigens, and release cytokines, which are tiny molecules that attract other immune cells to the area.
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Monocytes only circulate in the blood.
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Some monocytes migrate into tissues and differentiate into macrophages, which remain in tissues and aren't found in the blood.
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Dendritic cells are the prototypical antigen-presenting cell.
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Dendritic cells are usually found in sites that are in contact with most external antigens, like the skin epithelium or the gastrointestinal mucosa.
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When dendritic cells are young and immature, they're excellent at phagocytosis, constantly eating large amounts of protein found in the interstitial fluid.
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But when a dendritic cell phagocytosis is a pathogen, it's a life-changing, coming-of-age moment.
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mature dendritic cells will destroy the pathogen and break up its protein into short amino acid chains.
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Dendritic cells will then move through the lymph to the nearest lymph node and they'll perform an antigen presentation, which is where they present those amino acid chains,
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which are antigens, to T cells.
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Antigen presentation is what connects the innate and adaptive immune systems.
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Antigen presentation is something that can be done by dendritic cells, macrophages, as well as monocytes,
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which is why all of these cells are referred to as antigen-presenting cells.
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Dendritic cells are the best at this process because they are the only cells that live where pathogens enter, through the epithelial like skin, gut, and airways.
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And they are the only cells that can traffic from these tissues to lymph nodes, where T cells circulate.
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Now, only T cells with a receptor that can bind to the specific shape of the antigen will be activated, and that's called priming.
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It's similar to how a lock will only snap open when a key with a very specific shape goes in.
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However, T-cells can only see their antigen if it is presented to them on a silver platter, and on a molecular level,
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that platter is the major histocompatibility complex, or MHC for short.
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So the antigen-presenting cell will load the antigen on an MHC molecule and display it to T-cells, and when the right T-cell comes along, it binds.
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The final group of blood cells, the lymphocytes, includes B cells, T cells, and natural killer cells.
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B and T cells make up the adaptive immune response, while natural killer cells are part of the innate immune system.
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B cells and natural killer cells complete their development where they started,
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in the bone marrow, whereas some lymphoid progenitor cells migrate to the thymus where they develop into T cells.
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All of the lymphocytes are able to travel in and out of tissue and the bloodstream.
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Natural killer cells are large lymphocytes with granules, and they target cells infected with intracellular organisms,
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like viruses, as well as cells that pose a threat, like cancer cells.
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Natural killer cells kill their target cells by releasing cytotoxic granules.
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These granules contain molecules that punch holes in the target cell membrane by binding directly to the phospholipids and creating pores,
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and release some molecules that get inside the cell and cause target cells to undergo apoptosis, which is a type of programmed cell death.
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B cells, like T cells, also have a receptor on their surface that allows them to only bind to an antigen that has a very specific shape.
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The main difference is that B cells do not need antigens to be presented to them on an MHC molecule.
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They can simply bind to an antigen directly.
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When a B cell binds to a protein antigen that's on the surface of a pathogen, it's capable of internalizing that antigen, degrading it, and presenting it to T cells.
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So technically, they're also antigen-presenting cells as well.
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Like other antigen-presenting cells, the B cell loads the antigen onto an MHC molecule called MHC2 and displays it to T cells.
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When a T cell gets activated, it helps the B cell mature into a plasma cell, and a plasma cell can secrete lots and lots of antibodies.
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Typically, it takes a few weeks for antibody levels to peak.
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The antibodies, or immunoglobulins, have the exact same antigen specificity as the B cell they came from.
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Antibodies are just the B cell receptor in a secreted form, so they can circulate in the plasma, which is the noncellular part of blood,
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attaching to pathogens and tagging them for destruction.
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Because antibodies aren't bound to cells and float freely in the blood, this is considered humoral immunity, a throwback to the term humors,
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which refers to body fluids.
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Now, the final type of lymphoid cell is the T cell, and it's in charge of cell-mediated immunity.
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T cells are antigen-specific, but they cannot secrete their antigen receptor.
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A naive T cell can be activated
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or primed to allow it to turn into a mature T cell by any of the antigen-presenting cells, but most often it's done by a dendritic cell.
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Now, there are two main types of T-cells, CD4 T-cells and CD8 T-cells, where CD stands for cluster of differentiation.
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There are hundreds of CD markers in the immune system, and these CD markers are useful in telling different cells apart.
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For example, all T-cells are CD3 positive because CD3 is part of the T-cell antigen receptor.
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So CD4 positive T cells are actually CD3 positive, CD4 positive.
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And these cells are called helper cells because they're like generals on the battlefield.
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They secrete cytokines that help coordinate the efforts of macrophages and B cells.
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Helper T cells can only see their antigen if it's presented on an MHC2 molecule.
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CD8 positive T cells are CD3 positive, CD8 positive, and they're called cytotoxic T cells because they kill target cells,
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really similarly to how natural killer cells do it, with one major difference.
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CD8 positive T cells only kill cells that present a specific antigen on an MHC1 molecule, which is structurally similar to the MHC2 molecule,
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whereas natural killer cells aren't nearly as specific in who they kill.
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So, now let's go through a complete immune response with a bacterial pathogen in the lungs.
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To start, the bacteria will have to get breathed in, slip by your nose hairs, past the cilia in the airways,
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and will then have to penetrate past the epithelium layer of the lungs.
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Once it's in the lung tissue, the bacteria will start to divide and might encounter a resident macrophage in the lung tissue, which will ingest the bacteria and start releasing cytokines.
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Those cytokines start the inflammatory process by making blood vessels leaky and attracting nearby eosinophils,
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basophils, and mast cells, which release their own cytokines and granules, amplifying the inflammation.
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Neutrophils from the blood, as well as fresh new ones from the bone marrow, dive into the tissue and join the battle.
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If the pathogen was a virus, natural killer cells would help destroy the infected cells at this point.
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This is all part of the innate immune response.
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Around this point in the infection, immature dendritic cells residing under the epithelium digest the pathogens
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and move from the lung tissue over to a nearby lymph
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node where they present the processed antigen on an MHC2 protein to a naive T cell.
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The dendritic cell, which is part of the innate immune response, bridges the innate and the adaptive immune responses when it presents the antigen to the T cell,
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which is part of the adaptive immune response.
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Sometimes, if the infection is spreading, bacteria might find its way to a lymph node without the help of a dendritic cell.
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In this case, B cells, part of the adaptive immune response,
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might directly phagocytose the bacteria and present it to a naive CD4 positive T cell.
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Either way, if the antigen is the right fit for the T cell, the T cell will begin to differentiate and undergo clonal expansion.
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Differentiated CD4 positive T cells will release cytokines that will induce B cells to differentiate into plasma cells,
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which secrete antibodies that will go into the lymph and then into the bloodstream.
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The antibodies will tag pathogens, making it easier for the phagocytes to eat them.
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Some cytokines will activate macrophages to kill bacteria that have been phagocytized, but cannot be killed by the macrophage alone unless it gets help from its friends,
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the T-cells, of course.
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If the pathogen was a virus living and replicating in the cytoplasm of the infected cells,
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the CD8-positive T-cells would kill any infected cells that express the viral antigen on an MHC1.
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Over time, as the invading pathogen dies off, most of the B and T cells die of neglect, but a few turn into memory B cells and memory T cells,
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which linger for years in case they're needed in the future.
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All right, as a quick recap, the immune system has an innate and an adaptive response.
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The innate immune response is immediate but nonspecific and lacks memory.
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Whereas the adaptive immune response is highly specific and remembers everything, but it takes several days to get started and almost two weeks to peak.
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Helping current and future clinicians focus, learn, retain, and thrive.
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Learn more.
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Thank you.
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المفردات وملاحظات التحدث لهذا الدرس
يحتوي هذا الفيديو على 159 جملة و2581 كلمة للتدرب على الترديد. مدة الكلام 16:26. يتكلم المتحدث بسرعة طبيعية، نحو 157 كلمة في الدقيقة، قريبة من المحادثة اليومية. 70% فقط من الكلمات ضمن أكثر 3,000 كلمة شيوعًا في الإنجليزية، فالمفردات صعبة نسبيًا.
أهم المفردات في هذا الفيديو
15 كلمة من الفيديو تستحق التعلّم، مع النطق والمعنى:
| الكلمة | النطق | المعنى |
|---|---|---|
| immune صفة | /ɪˈmjuːn/ | مَنِيع |
| molecule اسم | /ˈmɑ.lɪ.kjul/ | جُزَيْء |
| tissue اسم | /ˈtɪʃ.(j)u/ | مَنْدِيل, مِنْدِيل |
| killer اسم | /ˈkɪlɚ/ | قَاتِل, قَاتِلَة |
| receptor اسم | /ɹɪˈsɛp.tə/ | مُسْتَقْبِل |
| activate فعل | /ˈæktɪˌveɪt/ | فَعَّلَ |
| lung اسم | /ˈlʌŋ/ | رِئَة, سَحَر |
| differentiate فعل | /dɪf.əˈɹɛn.ʃi.eɪt/ | فَرَّقَ |
| bone اسم | /boʊn/ | عَظْم, عضم |
| whereas | /(h)wɛɹˈæz/ | عِنْدَمَا |
| plasma اسم | /ˈplæzmə/ | بِلَزْمَا |
| inflammatory صفة | /ɪnˈflæmət(ə)ɹi/ | تَحْرِيضِيّ |
| marrow اسم | /ˈmæɹəʊ/ | نِقْيُ ٱلْعَظْم, مُخُّ ٱلْعَظْم |
| acid اسم | /ˈæsɪd/ | حَامِض, حَمْض |
| virus اسم | /ˈvaɪ.ɹəs/ | ڤِيرُوس, فِيرُوس |
نطق يحتاج إلى انتباه
يستخدم المتحدث 14 من الصيغ المختصرة، مثل they're, aren't, doesn't. انطقها بصيغتها القصيرة كما تسمعها.
- أصوات “th”: thrive /θɹajv/, pathogen /ˈpæθəd͡ʒn̩/, epithelium /ˌɛpɪˈθiːlɪəm/
- أصوات “sh” و“zh”: tissue /ˈtɪʃ.(j)u/, differentiate /dɪf.əˈɹɛn.ʃi.eɪt/, presentation /ˌpɹɛzn̩ˈteɪʃn̩/, infection /ɪnˈfɛkʃən/, distinguish /dɪˈstɪŋ.ɡwɪʃ/
- الكلمات الطويلة — انتبه لموضع النبر: differentiate /dɪf.əˈɹɛn.ʃi.eɪt/, inflammatory /ɪnˈflæmət(ə)ɹi/, immunity /ɪˈmjuːnəti/, mechanism /ˈmɛk.ə.nɪ.zəm/, eliminate /ɪˈlɪm.ɪ.neɪt/
كيف تتدرب بهذا الفيديو
- استمع إلى الفيديو كاملًا مرة واحدة دون أن تتكلم، ودوّن الكلمات التي لا تعرفها.
- ابدأ بسرعة 0.75×، وردّد جملة جملة، ثم عُد إلى السرعة العادية عندما يصبح الأمر سهلًا.
- سجّل صوتك وقارنه بالأصل، مع الانتباه إلى كلمات مثل immune, molecule, tissue.
القواعد في هذا الفيديو
أكثر التراكيب التي يستخدمها المتحدث، مع العبارات نفسها من الفيديو:
| التركيب | في الفيديو |
|---|---|
| المبني للمجهول be + اسم المفعول — التركيز على ما يحدث لا على من يفعله | being surrounded · is made · being primed |
| جمل الوصل who / which + جملة — معلومة إضافية عن شخص أو شيء | expansion, which means · soldiers, which are · cell, which can |
| المضارع التام have/has + اسم المفعول — حدث ماضٍ ما زال له أثر الآن | has been ingested · have been phagocytized |
ما هي تقنية التظليل الصوتي؟
التظليل الصوتي (Shadowing) تقنية تعلم لغة مدعومة علمياً، طُورت أصلاً لتدريب المترجمين الفوريين المحترفين. الطريقة بسيطة لكنها قوية: تستمع لصوت إنجليزي أصلي وتكرره فوراً بصوت عالٍ — كظل يتبع المتحدث بتأخير 1-2 ثانية. تُظهر الأبحاث تحسناً كبيراً في دقة النطق والتنغيم والإيقاع وربط الأصوات والاستماع والطلاقة.