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answers to ap bio immune system guideThank you for your patience! Your body’s immune system is there to protect you, both from inside and outer-body offenses. Animals must defend themselves against viruses, bacteria, and other types of intruders. Our cells have no walls, as we traded in mobility for susceptibility over the course of evolution. So our immune system is there to help keep us safe.Viruses have been a topic for discussion over a long time as they are rather unique in both their structure and function. Viruses do not have cells. They need energy from their environment, as they can’t maintain an internal stable environment on their own. They are no considered to be alive, yet do take great strides to replicate themselves. Lysogenic virus DNA hides in your chromosomes and generally remains dormant. It does not automatically cause disease. Lytic viruses destroy the cell. To lyse something is essentially to cut it up, or destroy it. There is a lytic phase to many viruses in which they copy themselves and then destroy the host cell before moving on to other cells in the body. The flu is an example of this type of virus. It attached to a host cell, injects its DNA (or if it uses RNA, then it undergoes reverse transcription to have DNA available), and then the lytic cycle turns off the cell’s machinery and forces it to make proteins for the virus. It’s dormant, and when the cells divide, the DNA from the virus also divides and is copied. Occasionally, there may be a stimulus that drives it out of the chromosome and into a lytic cycle. Most viruses are actually a bit of both, part lysogenic, part lytic. They may lean more heavily to one side, as in the flu virus, which exists mostly in a lytic phase. Viruses can generally only be prevented with vaccines, though bacteria can be cured with antibiotics. The first lines of defense are physical barriers such as skin and mucus membranes. The second is non-specific, as well, but internal. This would include phagocytic white blood cells.http://sirinthepgroup.com/userfiles/eh-black-finger-manual.xml
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The third and last line of defense is what’s typically referred to as the immune system. This includes lymphocytes and antibodies, more specific to definitive types of invaders. Image Source: Wikimedia Commons. This involves the skin, respiratory system, digestive tract, and genito-urinary tract. These are most exposed to the outside world. Sweat has an acidic pH and can help to prevent bacterial infections. Stomach acid also has a low pH. Tears, saliva, and mucus have antimicrobial properties, themselves, and can serve to trap potential invaders and neutralize them. Lysosomes within the saliva digest the cell walls of bacteria and destroy them. They are phagocytic cells, which is to say they eat other cells. They also have microbial proteins and work with inflammatory responses. There are several types of white blood cells, and these are basophils, eosinophil, neutrophils monocytes, and lymphocytes. Monocytes and neutrophils are phagocytic and digest invaders with enzymes. Monocytes start as cells and become macrophages. Most white blood cells are neutrophils, which are rather short-lived cells, which neutralize invaders. Eosinophils fight parasites. Basophils are part of an inflammatory response and produce histamine. This makes the blood vessels more leaky, which allows fluids to leave and enter more easily, which allow for the more efficient transport of white blood cells to a site. As they are also involved in inflammatory responses, the temperature in the area may go up then, and swelling will occur. This resets the body’s thermostat. The higher temperatures are helpful in that they can inhibit the growth of microbes, facilitate phagocytosis, and speed up the repair of tissues. Lymph fluid moves throughout the body by way of contractions of muscles and vessel with one-way valves. Lymph nodes are located in certain parts of the body and act as little police stations, all containing a large number of lymphocytes and macrophages. T cells mature in the thymus.http://www.newgo.ru/media/egyptian-hakim-rifle-manual.xml They are attracted by chemical signals, the process of which is referred to as positive chemotaxis. In this way, lymphocytes are able to respond to specific toxins, microorganisms, abnormal body cells, and antigens (which in general, is just anything that elicits an immune response). Once the signal triggers a response from them, they move faster and look to destroy invaders. B cells produce antibodies to remember the chemical print of a foreign invader and allow for faster responses in the future. T cells facilitate the production of chemicals used by lymphocytes to kill off the foreign particles. B cells are spurned to reproduce clone colonies, clone cells being either plasma cells or memory cells. Plasma cells facilitate the immediate production of antibodies, and release them in the short-term. Memory cells are for long-term immunity. They produce plasma cells to fight off invaders if they recognize the same foreign particle at a later date. These play a big role in vaccines. B cells recognize intact antigens, and T cells recognize antigen fragments. If it’s designed to work against e. coli, for example, that is the only invader it works against. They are multi-chain proteins produced by B cells that “tag” invaders as being foreign so other cells can recognize them as invaders. In neutralization, it would bind to a locking site on a virus so that it can’t take over a cell then. With agglutination, it causes invaders to clump up. The reason this helps is this: think of peas. Is it easier to get one pea off a plate to eat, or use a spoon to eat many at once. When bacteria are clumped up, and a white blood cell finds it, it eats up the entire clump. Precipitation is where antigens are connected together by antibodies and they become dense and separate out the bad parts from the rest of the blood. And in a complement reaction, antibodies bind to a foreign cell, and complement proteins form and encircle the invader, and a hole is put in the ring and the cell dies. Plasma cells are typically involved in this type of attack. An antigen binds with a B cell and then it’s triggered to make many, many copies of itself. Clones can become memory cells or plasma cells. If it happens again, it is much faster. Memory cells stick around after a first attack and the antibody concentration becomes much higher far more quickly if the same invader comes back. Vaccines are a form of active immunity. They stimulate the immune system to produce a response of its own. This is most effective against viral diseases. A person receives antibodies only in this case. An example would be a mother making antibodies and passing them to her child by way of breast-feeding. If the child stops breast-feeding, it will no longer have those antibodies. Antivenom works in a similar way. Scientists inject rabbits with snake venom and the rabbits produce antibodies. The antibodies are separated, and now you have an antivenom. Those antibodies will lock up the proteins in venom and serve to neutralize them. MHC (major histocompatibility complex) tells the body what is a part of itself, and develops early in life. T cells use this in knowing what to go after. Helper T cells stimulate immune components while cytotoxic T cells kill off cells. If you have an invading bacterial infection, they would be taken up by a macrophage in response. Now the macrophage becomes APC (antigen present cells) and presents an antigen on the outside of the cell for MHC to recognize. Helper T cells are activated and then activate the cytotoxic T cells to destroy cells with that same antigen mark. Cytotoxic T cells bind to infected cells and produce a protein called perferin which perforates that alien cells to rip them apart. Remember all three lines of defenses and the different types of cells that play a role, including B and T cells. If you're an educator interested in trying Albert, click the button below to learn about our pilot program. Learn how your comment data is processed. Sign up today for a sample of Albert’s premium practice content across high school and middle school subjects. Practice: The immune system Sort by: Top Voted Viral replication: lytic vs lysogenic The immune system Up Next The immune system Biology is brought to you with support from the Amgen Foundation Biology is brought to you with support from the Our mission is to provide a free, world-class education to anyone, anywhere. Khan Academy is a 501(c)(3) nonprofit organization. Donate or volunteer today. Innate immunity Adaptive immunity Role of phagocytes in innate or nonspecific immunity Types of immune responses: Innate and adaptive, humoral vs. Innate immunity Adaptive immunity Role of phagocytes in innate or nonspecific immunity Types of immune responses: Innate and adaptive, humoral vs.Khan Academy is a 501(c)(3) nonprofit organization. We can't connect to the server for this app or website at this time. There might be too much traffic or a configuration error. Try again later, or contact the app or website owner. It looks like your browser needs updating. For the best experience on Quizlet, please update your browser. Learn More. Innate Immunity First part of it is barrier defense (such as skin or shell). Also includes molecules (such as phagocytic cells, natural killer cells, antimicrobial proteins) that recognize traits shared by a broad class of pathogens. Lysozyme Enzyme in digestive system that break down peptidoglycan in bacterial cell walls. Phagocytosis Begins when a substance is engulfed by cell by endocytosis. A vacuole then forms and fuses with a lysosome. Components of the lysosome destroy the pathogen. Barrier defenses of vertebrates The skin is the most obvious barrier defense. Tight junctions help keep pathogens out. Also, mucus helps trap small particles. Lysozyme's are present in tears, saliva, and mucous. The acidic environment of the stomach also counts. Toll like Receptor Proteins found on phagocytic cells that Bind to fragments of molecules that are characteristic of a broad class of pathogens, triggering a response. Dendritic cell One type of antigen presenting cell. Mainly populate tissues that are exposed to the environment. They are involved in adaptive immunity. Eosinophils Often found beneath mucus layers, help destroy multicellular pathogens. Natural killer cells Type of innate defense cell. Destory cells that have abnormal surface proteins (such as virally infected cells or cancer cells). Interferons Proteins released from infected cells that interfere with viral infections in neighboring cells Complement System 30 proteins from blood plasma that are activated by microbial surface proteins. Inflammatory Response Changes brought on by signaling molecules following injury or infection. Begins when mast cells detect injury and release histamine, causing blood vessel dilation. Nuetrophils are then attracted. Nuetrophils digest pathogens and debris at the site of injury. Histamine Signaling molecule found in mast cells that tells blood vessels to dilate. Cytokines Signaling molecules that promote blood flow to site of injury or infection, thus increasing delivery of antimicrobial peptides. Lymphocytes T and B cells, white blood cells that derive from lymphoid stem cells. Thymus Organ in thoracic cavity above heart, where T cells mature. Antigen Substance that causes response from lymphocytes. Epitope Small, accessible portion of an antigen that binds to lymphocyte receptors. Antibodies Secreted B cell antigen receptors. Major histocompatibility complex Proteins that display protein fragments. Class I's are found on body cells, and class II's are found on antigen presenting cells. Antigen presentation Display of antigen fragment on MHC protein. 4 Major characteristics of adaptive immunity 1. Diversity of lymphocytes. 2. Self-tolerance. 3. Proliferation, clonal selection. 4. Immunological memory. Recombinase Enzyme complex that randomly links V and J segments of antigen receptor genes, creating millions of different types. Effector cells Short lived cells that quickly take effect against pathogens. Plasma cells Effector forms of B cells, secrete antibodies. Memory cells Long lived cells that give rise to effector cells if necessary. Clonal selection The process by which an encounter with an antigen selects which lymphocyte will divide. Primary immune response Production of effector cells. Secondary immune response Second, quicker response to the same antigen. Humoral immune response Process by which antibodies help neutralize and eliminate toxins. Cell-mediated immune response When cytotoxic t cells selectively destroy infected host cells. Helper t cell Triggers both humoral and cell-mediated responses. 1. Specific helper T cell binds to antigen displayed by class II MHC. CD4 helps mediate this interaction. In response to this joining, the antigen-presenting cell secretes cytokines. 2. The cytokines stimulate proliferation of identical helper T cells. 3. Helper T cells secrete cytokines, activating B cells and cytotoxic T cells. Antigen presenting cell Engulf and displays antigens. Can be dendritic cell, macrophage, or B cell. Cytotoxic T cells Use toxic proteins (perforins and granzymes) to kill infected cells. Interaction with infected cells starts when the antigen receptor attaches (with the help of CD8) to antigen presented by class I MHC. The T cells then kill the cell using performs and granzymes. Activation of B cell Helper T cells and B cells with same antigen receptor interact with antigen presenting cell. Later, helper T cell activates B cell, which proliferates into plasma cells and memory cells. Effect of antibodies Neutralization: Antibodies bind to viral proteins, preventing the virus from infecting cells. Agglutination: When antibodies bind to multiple pathogens, forming a larger clump that is easier for phagocytes to deal with. Precipitation: When antibodies link dissolved antigen molecules together. Complement system: Antibodies activate complement proteins, which destroy the infected cell. Active immunity Defenses that arise when a pathogen infects the body. In essence, these defenses are created by the body. The bodies response to a pathogen is an example. Vaccination is also active. Passive immunity When exogenously derived defenses fight pathogens. For example, antibodies in the mother pass to the baby via the placenta. Immunization Process by which a small sample of a pathogen is purposely introduced to stimulate immunological memory. Monoclonal antibodies Antibodies prepared in culture from clones of a B cell. Used in research and medical diagnosis because of their ability to recognize specific proteins. Allergens Antigens that elicit hypersensitive responses. These responses start when plasma cells secrete antibodies for a specific antigen. Interaction of receptors, antigens, and mast cells lead to release of histamine and inflammatory symptoms. Autoimmune disease When immune system fights its own body cells. The Animal Body: Basic Form and Function 14.1 Animal Form and Function 14.2 Animal Primary Tissues 14.3 Homeostasis Chapter 15. Animal Nutrition and the Digestive System 15.1 Digestive Systems 15.2 Nutrition and Energy Production 15.3 Digestive System Processes 15.4 Digestive System Regulation Chapter 16. The Nervous System 16.1 Neurons and Glial Cells 16.2 How Neurons Communicate 16.3 The Central Nervous System 16.4 The Peripheral Nervous System 16.5 Nervous System Disorders Chapter 17. Sensory Systems 17.1 Sensory Processes 17.2 Somatosensation 17.3 Taste and Smell 17.4 Hearing and Vestibular Sensation 17.5 Vision Chapter 18. The Endocrine System 18.1 Types of Hormones 18.2 How Hormones Work 18.3 Regulation of Body Processes 18.4 Regulation of Hormone Production 18.5 Endocrine Glands Chapter 19. The Musculoskeletal System 19.1 Types of Skeletal Systems 19.2 Bone 19.3 Joints and Skeletal Movement 19.4 Muscle Contraction and Locomotion Chapter 20. The Respiratory System 20.1 Systems of Gas Exchange 20.2 Gas Exchange across Respiratory Surfaces 20.3 Breathing 20.4 Transport of Gases in Human Bodily Fluids Chapter 21. The Circulatory System 21.1. Overview of the Circulatory System 21.2. Components of the Blood 21.3. Mammalian Heart and Blood Vessels 21.4. Blood Flow and Blood Pressure Regulation Chapter 22. Osmotic Regulation and Excretion 22.1. Osmoregulation and Osmotic Balance 22.2. The Kidneys and Osmoregulatory Organs 22.3. Excretion Systems 22.4. Nitrogenous Wastes 22.5. Hormonal Control of Osmoregulatory Functions Chapter 23. The Immune System 23.1. Innate Immune Response 23.2. Adaptive Immune Response 23.3. Antibodies 23.4. Disruptions in the Immune System Chapter 24. Animal Reproduction and Development 24.1. Reproduction Methods 24.2. Fertilization 24.3. Human Reproductive Anatomy and Gametogenesis 24.4. Hormonal Control of Human Reproduction 24.5. Human Pregnancy and Birth 24.6. Fertilization and Early Embryonic Development 24.7. Organogenesis and Vertebrate Formation Appendix PowerPoints About the Authors Versioning History Adaptive immunity is an immunity that occurs after exposure to an antigen either from a pathogen or a vaccination. This part of the immune system is activated when the innate immune response is insufficient to control an infection. In fact, without information from the innate immune system, the adaptive response could not be mobilized. There are two types of adaptive responses: the cell-mediated immune response, which is carried out by T cells, and the humoral immune response, which is controlled by activated B cells and antibodies. Activated T cells and B cells that are specific to molecular structures on the pathogen proliferate and attack the invading pathogen. Their attack can kill pathogens directly or secrete antibodies that enhance the phagocytosis of pathogens and disrupt the infection. Adaptive immunity also involves a memory to provide the host with long-term protection from reinfection with the same type of pathogen; on re-exposure, this memory will facilitate an efficient and quick response. T cells are a key component in the cell-mediated response—the specific immune response that utilizes T cells to neutralize cells that have been infected with viruses and certain bacteria. There are three types of T cells: cytotoxic, helper, and suppressor T cells. Cytotoxic T cells destroy virus-infected cells in the cell-mediated immune response, and helper T cells play a part in activating both the antibody and the cell-mediated immune responses. Suppressor T cells deactivate T cells and B cells when needed, and thus prevent the immune response from becoming too intense. Not all antigens will provoke a response. For instance, individuals produce innumerable “self” antigens and are constantly exposed to harmless foreign antigens, such as food proteins, pollen, or dust components. The suppression of immune responses to harmless macromolecules is highly regulated and typically prevents processes that could be damaging to the host, known as tolerance. An antigen-presenting cell (APC) is an immune cell that detects, engulfs, and informs the adaptive immune response about an infection. When a pathogen is detected, these APCs will phagocytose the pathogen and digest it to form many different fragments of the antigen. Antigen fragments will then be transported to the surface of the APC, where they will serve as an indicator to other immune cells. Dendritic cells are immune cells that process antigen material; they are present in the skin (Langerhans cells) and the lining of the nose, lungs, stomach, and intestines. Sometimes a dendritic cell presents on the surface of other cells to induce an immune response, thus functioning as an antigen-presenting cell. Macrophages also function as APCs. Before activation and differentiation, B cells can also function as APCs. Within the phagolysosome, the components are broken down into fragments; the fragments are then loaded onto MHC class I or MHC class II molecules and are transported to the cell surface for antigen presentation, as illustrated in Figure 23.8. Note that T lymphocytes cannot properly respond to the antigen unless it is processed and embedded in an MHC II molecule. APCs express MHC on their surfaces, and when combined with a foreign antigen, these complexes signal a “non-self” invader. Once the fragment of antigen is embedded in the MHC II molecule, the immune cell can respond. Helper T- cells are one of the main lymphocytes that respond to antigen-presenting cells. Recall that all other nucleated cells of the body expressed MHC I molecules, which signal “healthy” or “normal.” An antigen from the bacterium is presented on the cell surface in conjunction with an MHC II molecule Lymphocytes of the adaptive immune response interact with antigen-embedded MHC II molecules to mature into functional immune cells. Recall that the T cells are involved in the cell-mediated immune response, whereas B cells are part of the humoral immune response. Some T cells respond to APCs of the innate immune system, and indirectly induce immune responses by releasing cytokines. Other T cells stimulate B cells to prepare their own response. Another population of T cells detects APC signals and directly kills the infected cells. Other T cells are involved in suppressing inappropriate immune reactions to harmless or “self” antigens. T cells are able to recognize antigens. (credit: modification of work by NCI; scale-bar data from Matt Russell). T and B lymphocytes are also similar in that each cell only expresses one type of antigen receptor. Any individual may possess a population of T and B cells that together express a near limitless variety of antigen receptors that are capable of recognizing virtually any infecting pathogen. T and B cells are activated when they recognize small components of antigens, called epitopes, presented by APCs, illustrated in Figure 23.10. Note that recognition occurs at a specific epitope rather than on the entire antigen; for this reason, epitopes are known as “antigenic determinants.” In the absence of information from APCs, T and B cells remain inactive, or naive, and are unable to prepare an immune response. The requirement for information from the APCs of innate immunity to trigger B cell or T cell activation illustrates the essential nature of the innate immune response to the functioning of the entire immune system. A given antigen may contain several motifs that are recognized by immune cells. Each motif is an epitope. In this figure, the entire structure is an antigen, and the orange, salmon and green components projecting from it represent potential epitopes. These molecules are important because they regulate how a T cell will interact with and respond to an APC. The two populations of T cells have different mechanisms of immune protection, but both bind MHC molecules via their antigen receptors called T cell receptors (TCRs). The CD4 or CD8 surface molecules differentiate whether the TCR will engage an MHC II or an MHC I molecule. Because they assist in binding specificity, the CD4 and CD8 molecules are described as coreceptors. The mammalian adaptive immune system is adept in responding appropriately to each antigen. Mammals have an enormous diversity of T cell populations, resulting from the diversity of TCRs. Each TCR consists of two polypeptide chains that span the T cell membrane, as illustrated in Figure 23.12; the chains are linked by a disulfide bridge. Each polypeptide chain is comprised of a constant domain and a variable domain: a domain, in this sense, is a specific region of a protein that may be regulatory or structural. The intracellular domain is involved in intracellular signaling. A single T cell will express thousands of identical copies of one specific TCR variant on its cell surface. The specificity of the adaptive immune system occurs because it synthesizes millions of different T cell populations, each expressing a TCR that differs in its variable domain. This TCR diversity is achieved by the mutation and recombination of genes that encode these receptors in stem cell precursors of T cells. The binding between an antigen-displaying MHC molecule and a complementary TCR “match” indicates that the adaptive immune system needs to activate and produce that specific T cell because its structure is appropriate to recognize and destroy the invading pathogen. These cells are important for extracellular infections, such as those caused by certain bacteria, helminths, and protozoa. T H lymphocytes recognize specific antigens displayed in the MHC II complexes of APCs. There are two major populations of T H cells: T H 1 and T H 2. T H 1 cells secrete cytokines to enhance the activities of macrophages and other T cells. T H 1 cells activate the action of cyotoxic T cells, as well as macrophages. T H 2 cells stimulate naive B cells to destroy foreign invaders via antibody secretion. Whether a T H 1 or a T H 2 immune response develops depends on the specific types of cytokines secreted by cells of the innate immune system, which in turn depends on the nature of the invading pathogen. Recall the frontline defenses of macrophages involved in the innate immune response. Some intracellular bacteria, such as Mycobacterium tuberculosis, have evolved to multiply in macrophages after they have been engulfed. These pathogens evade attempts by macrophages to destroy and digest the pathogen. When M. tuberculosis infection occurs, macrophages can stimulate naive T cells to become T H 1 cells. These stimulated T cells secrete specific cytokines that send feedback to the macrophage to stimulate its digestive capabilities and allow it to destroy the colonizing M. tuberculosis. In the same manner, T H 1-activated macrophages also become better suited to ingest and kill tumor cells. In summary; T H 1 responses are directed toward intracellular invaders while T H 2 responses are aimed at those that are extracellular. A plasma cell is an immune cell that secrets antibodies; these cells arise from B cells that were stimulated by antigens. Similar to T cells, naive B cells initially are coated in thousands of B cell receptors (BCRs), which are membrane-bound forms of Ig (immunoglobulin, or an antibody). The B cell receptor has two heavy chains and two light chains connected by disulfide linkages. Each chain has a constant and a variable region; the latter is involved in antigen binding. Two other membrane proteins, Ig alpha and Ig beta, are involved in signaling. The receptors of any particular B cell, as shown in Figure 23.13 are all the same, but the hundreds of millions of different B cells in an individual have distinct recognition domains that contribute to extensive diversity in the types of molecular structures to which they can bind. In this state, B cells function as APCs. They bind and engulf foreign antigens via their BCRs and then display processed antigens in the context of MHC II molecules to T H 2 cells. When a T H 2 cell detects that a B cell is bound to a relevant antigen, it secretes specific cytokines that induce the B cell to proliferate rapidly, which makes thousands of identical (clonal) copies of it, and then it synthesizes and secretes antibodies with the same antigen recognition pattern as the BCRs. The activation of B cells corresponding to one specific BCR variant and the dramatic proliferation of that variant is known as clonal selection. This phenomenon drastically, but briefly, changes the proportions of BCR variants expressed by the immune system, and shifts the balance toward BCRs specific to the infecting pathogen. The signal transduction region transfers the signal into the cell. Although T and B cells both react with molecules that are termed “antigens,” these lymphocytes actually respond to very different types of molecules. B cells must be able to bind intact antigens because they secrete antibodies that must recognize the pathogen directly, rather than digested remnants of the pathogen. Bacterial carbohydrate and lipid molecules can activate B cells independently from the T cells. The cell-mediated part of the adaptive immune system consists of CTLs that attack and destroy infected cells. CTLs are particularly important in protecting against viral infections; this is because viruses replicate within cells where they are shielded from extracellular contact with circulating antibodies. These resulting CTLs then identify non-APCs displaying the same MHC I-embedded antigens (for example, viral proteins)—for example, the CTLs identify infected host cells. CTLs attempt to identify and destroy infected cells before the pathogen can replicate and escape, thereby halting the progression of intracellular infections. CTLs also support NK lymphocytes to destroy early cancers. Cytokines secreted by the T H 1 response that stimulates macrophages also stimulate CTLs and enhance their ability to identify and destroy infected cells and tumors. Binding of TCRs with antigens activates CTLs to release perforin and granzyme, degradative enzymes that will induce apoptosis of the infected cell. Recall that this is a similar destruction mechanism to that used by NK cells. In this process, the CTL does not become infected and is not harmed by the secretion of perforin and granzymes. In fact, the functions of NK cells and CTLs are complementary and maximize the removal of infected cells, as illustrated in Figure 23.14. If the NK cell cannot identify the “missing self” pattern of down-regulated MHC I molecules, then the CTL can identify it by the complex of MHC I with foreign antigens, which signals “altered self.