Immune system defense -
Acquired immunity is immunity that develops with exposure to various antigens. Your immune system builds a defense against that specific antigen. Passive immunity is due to antibodies that are produced in a body other than your own.
Infants have passive immunity because they are born with antibodies that are transferred through the placenta from their mother. These antibodies disappear between ages 6 and 12 months.
Passive immunization may also be due to injection of antiserum, which contains antibodies that are formed by another person or animal. It provides immediate protection against an antigen, but does not provide long-lasting protection.
Immune serum globulin given for hepatitis exposure and tetanus antitoxin are examples of passive immunization. The immune system includes certain types of white blood cells. It also includes chemicals and proteins in the blood, such as antibodies, complement proteins, and interferon.
Some of these directly attack foreign substances in the body, and others work together to help the immune system cells. As lymphocytes develop, they normally learn to tell the difference between your own body tissues and substances that are not normally found in your body.
Once B cells and T cells are formed, a few of those cells will multiply and provide "memory" for your immune system. This allows your immune system to respond faster and more efficiently the next time you are exposed to the same antigen. In many cases, it will prevent you from getting sick.
For example, a person who has had chickenpox or has been immunized against chickenpox is immune from getting chickenpox again. The inflammatory response inflammation occurs when tissues are injured by bacteria, trauma, toxins, heat, or any other cause. The damaged cells release chemicals including histamine, bradykinin, and prostaglandins.
These chemicals cause blood vessels to leak fluid into the tissues, causing swelling. This helps isolate the foreign substance from further contact with body tissues. The chemicals also attract white blood cells called phagocytes that "eat" germs and dead or damaged cells. This process is called phagocytosis.
Phagocytes eventually die. Pus is formed from a collection of dead tissue, dead bacteria, and live and dead phagocytes. Immune system disorders occur when the immune response is directed against body tissue, is excessive, or is lacking.
Allergies involve an immune response to a substance that most people's bodies perceive as harmless. Vaccination immunization is a way to trigger the immune response.
Small doses of an antigen, such as dead or weakened live viruses, are given to activate immune system "memory" activated B cells and sensitized T cells. Memory allows your body to react quickly and efficiently to future exposures.
An efficient immune response protects against many diseases and disorders. An inefficient immune response allows diseases to develop. Too much, too little, or the wrong immune response causes immune system disorders. An overactive immune response can lead to the development of autoimmune diseases , in which antibodies form against the body's own tissues.
Innate immunity; Humoral immunity; Cellular immunity; Immunity; Inflammatory response; Acquired adaptive immunity. Abbas AK, Lichtman AH, Pillai S. Properties and overview of immune responses.
In: Abbas AK, Lichtman AH, Pillai S, eds. Cellular and Molecular Immunology. Philadelphia, PA: Elsevier; chap 1. Bankova L, Barrett N. Innate immunity. In: Burks AW, Holgate ST, O'Hehir RE, et al, eds.
Middleton's Allergy: Principles and Practice. Firestein GS, Stanford SM. Mechanisms of inflammation and tissue repair.
In: Goldman L, Schafer AI, eds. Goldman-Cecil Medicine. Philadelphia, PA: Elsevier; chap They specialize in identifying cells that are infected by a virus or that have become tumorous. To do this, they search for cells that have changes in their surface, and then destroy the cell surface using cell toxins.
The adaptive immune system takes over if the innate immune system is not able to destroy the germs. It specifically targets the type of germ that is causing the infection.
But to do that it first needs to identify the germ. This means that it is slower to respond than the innate immune system, but when it does it is more accurate. It also has the advantage of being able to "remember" germs, so the next time a known germ is encountered, the adaptive immune system can respond faster.
The second infection is then usually not even noticed, or is at least milder. T lymphocytes also called T cells are produced in bone marrow and then move to the thymus through the bloodstream, where they mature. The "T" in their name comes from "thymus. T cells have detection features on their surfaces that can attach to germs — like a lock that one particular key will fit.
The immune system can produce a matching T cell type for each germ in an infection within a few days. Then if a germ attaches to a matching T cell, the T cell starts to multiply — creating more T cells specialized to that germ. Because only the cells that match the germ multiply, the immune response is customized.
B lymphocytes B cells are made in the bone marrow and then mature there to become specialized immune system cells. They take their name from the "B" in "bone marrow.
The B cells are activated by the T helper cells: T helper cells contact B cells that match the same germs that they do. This activates the B cells to multiply and to transform themselves into plasma cells.
These plasma cells quickly produce very large amounts of antibodies and release them into the blood. Because only the B cells that match the attacking germs are activated, only the exact antibodies that are needed will be produced.
Some of the activated B cells transform into memory cells and become part of the "memory" of the adaptive immune system. The various cells of the adaptive immune system communicate either directly or via soluble chemical messengers such as cytokines small proteins.
These chemical messengers are mostly proteins and are produced by different cells in the body. Antibodies are compounds of protein and sugar that circulate in the bloodstream. They are created by the immune system to fight germs and foreign substances.
Antibodies can quickly detect germs and other potentially harmful substances, and then attach to them. This neutralizes the "intruders" and attracts other immune system cells to help.
Antibodies are produced by the B lymphocytes. Germs and other substances that can provoke the creation of antibodies are also referred to as "antigens. An antibody only attaches to an antigen if it matches exactly, like a key in the lock of the antibody. That is how antibodies detect the matching germs to initiate a fast response from the adaptive immune system.
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Show details Cologne, Germany: Institute for Quality and Efficiency in Health Care IQWiG ; Search term. The innate and adaptive immune systems Last Update: July 30, ; Next update: The innate immune system: Fast and general effectiveness The innate immune system is the body's first line of defense against germs entering the body.
The innate immune system consists of Protection offered by the skin and mucous membranes. Protection offered by the skin and mucous membranes All outer and inner surfaces of the human body a key part of the innate immune system.
Protection offered by the immune system cells defense cells and proteins The innate immune system activates special immune system cells and proteins if germs get past the skin and mucous membranes and enter the body.
What happens during an inflammation? Certain proteins enzymes are also activated to help in the immune response see below. Scavenger cells: Neutralizing germs Bacteria or viruses that enter the body can be stopped right away by scavenger cells phagocytes.
The role of proteins Several proteins enzymes help the cells of the innate immune system. The tasks of these enzymes include: marking germs as targets for scavenger cells,. destroying bacteria cell walls to kill them, and. fighting viruses by destroying the viral envelope the outermost layer of a virus or cells that have been infected with viruses.
Natural killer cells: Searching for changed body cells The natural killer cells are the third major part of the innate immune system. The adaptive immune system: Fighting the germs directly The adaptive immune system takes over if the innate immune system is not able to destroy the germs.
The adaptive immune system is made up of: T lymphocytes in the tissue between the body's cells. T lymphocytes T lymphocytes also called T cells are produced in bone marrow and then move to the thymus through the bloodstream, where they mature.
Some T helper cells become memory T cells after the infection has been defeated. They can "remember" which germs were defeated and are then ready to activate the adapted immune system quickly if there is another infection. B lymphocytes B lymphocytes B cells are made in the bone marrow and then mature there to become specialized immune system cells.
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The antibodies defenee mark these antigens for destruction. There are many cells, proteins and chemicals involved in this attack. The complement system is sjstem up of proteins whose actions complement the work done by antibodies.
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Immunoglobulins commonly Immune system defense as antibodies are used dystem treat ssytem who are unable to make enough ddefense their own, or whose antibodies do not work defese. This treatment is known as immunoglobulin replacement therapy IRT External Link.
Until recently, immunoglobulin therapy in Australia mostly involved delivery defensf immunoglobulins through a drip into the vein — Immjne as intravenous immunoglobulin IVIg therapy.
Now, subcutaneous defenae SCIg detense Immune system defense Defwnse can be delivered into the fatty defensf under the skin, which may defenes benefits for some patients. This is known as subcutaneous infusion or Immune system defense therapy.
Immunw immunoglobulin is similar to intravenous immunoglobulin. It is made from plasma — the liquid part of blood containing important proteins like antibodies. Download the Subcutaneous Immunoglobulin - information sheet for patients External Link to read more about this type of treatment.
Many health services are now offering SCIg therapy to eligible patients with specific immune conditions. Immunisation works by copying the body's natural immune response. A vaccine a small amount of a specially treated virus, bacterium or toxin is injected into the body.
The body then makes antibodies to it. If a vaccinated person is exposed to the actual virus, bacterium or toxin, they won't get sick because their body will recognise it and know how to attack it successfully.
Vaccinations are available against many diseases, including measles and tetanus. The immunisations you may need are decided by your health, age, lifestyle and occupation.
Together, these factors are referred to as HALO, which is defined as:. View the HALO infographic External Link to find out more. This page has been produced in consultation with and approved by:. Content on this website is provided for information purposes only.
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Actions for this page Listen Print. Summary Read the full fact sheet. On this page. Immune system The immune system and microbial infection Parts of the immune system The body's other defences against microbes Fever is an immune system response Common disorders of the immune system Immunisation Where to get help.
Immune system The immune system is made up of a complex network of organs, cells and proteins that fight infection microbes. The immune system and microbial infection The immune system External Link keeps a record of every microbe it has ever defeated, in types of white blood cells B-lymphocytes and T-lymphocytes known as memory cells.
Parts of the immune system The main parts of the immune system are: white blood cells antibodies complement system lymphatic system spleen bone marrow thymus.
White blood cells White blood cells are the key players in your immune system. Antibodies Antibodies help the body to fight microbes or the toxins poisons they produce. Complement system The complement system is made up of proteins whose actions complement the work done by antibodies. Lymphatic system The lymphatic system is a network of delicate tubes throughout the body.
The main roles of the lymphatic system are to: manage the fluid levels in the body react to bacteria deal with cancer cells deal with cell products that otherwise would result in disease or disorders absorb some of the fats in our diet from the intestine.
The lymphatic system is made up of: lymph nodes also called lymph glands — which trap microbes lymph vessels — tubes that carry lymph, the colourless fluid that bathes your body's tissues and contains infection-fighting white blood cells white blood cells lymphocytes.
Spleen The spleen is a blood-filtering organ that removes microbes and destroys old or damaged red blood cells. Bone marrow Bone marrow is the spongy tissue found inside your bones. Thymus The thymus filters and monitors your blood content.
The body's other defences against microbes As well as the immune system, the body has several other ways to defend itself against microbes, including: skin — a waterproof barrier that secretes oil with bacteria-killing properties lungs — mucous in the lungs phlegm traps foreign particles, and small hairs cilia wave the mucous upwards so it can be coughed out digestive tract — the mucous lining contains antibodies, and the acid in the stomach can kill most microbes other defences — body fluids like skin oil, saliva and tears contain anti-bacterial enzymes that help reduce the risk of infection.
The constant flushing of the urinary tract and the bowel also helps. Fever is an immune system response A rise in body temperature, or fevercan happen with some infections.
Common disorders of the immune system It is common for people to have an over- or underactive immune system. Overactivity of the immune system External Link can take many forms, including: allergic diseases — where the immune system makes an overly strong response to allergens.
Allergic diseases are very common. They include: allergies to foodsmedications or stinging insects anaphylaxis life-threatening allergy hay fever allergic rhinitis sinus disease asthma hives urticaria dermatitis eczema. autoimmune diseases — where the immune system mounts a response against normal components of the body.
Autoimmune diseases range from common to rare. They include: multiple sclerosis autoimmune thyroid disease type 1 diabetes systemic lupus erythematosus rheumatoid arthritis systemic vasculitis. Immunoglobulin therapy Immunoglobulins commonly known as antibodies are used to treat people who are unable to make enough of their own, or whose antibodies do not work properly.
Immunisation Immunisation works by copying the body's natural immune response. Together, these factors are referred to as HALO, which is defined as: Health — some health conditions or factors may make you more vulnerable to vaccine-preventable diseases.
For example, premature birth, asthma, diabetes, heartlung, spleen or kidney conditions, Down syndrome and HIV will mean you may benefit from additional or more frequent immunisations.
Age — at different ages you need protection from different vaccine-preventable diseases. Australia's National Immunisation Program External Link sets out recommended immunisations for babies, children, older people and other people at risk, such as Aboriginal and Torres Strait Islanders.
Most recommended vaccines are available at no cost to these groups. Lifestyle — lifestyle choices can have an impact on your immunisation needs. Travelling overseas to certain placesplanning a family, sexual activitysmokingand playing contact sport that may expose you directly to someone else's blood, will mean you may benefit from additional or more frequent immunisations.
Occupation — you are likely to need extra immunisations, or need to have them more often, if you work in an occupation that exposes you to vaccine-preventable diseases or puts you into contact with people who are more susceptible to problems from vaccine-preventable diseases such as babies or young children, pregnant women, the elderly, and people with chronic or acute health conditions.
For example, if you work in aged care, childcare, healthcare, emergency services or sewerage repair and maintenance, discuss your immunisation needs with your doctor. Some employers help with the cost of relevant vaccinations for their employees.
ASCIA National Immunodeficiency Strategy for Australia and New Zealand External LinkAustralasian Society of Clinical Immunology and Allergy ASCIA.
: Immune system defense| Background | University Calcium and bone health South Carolina School of Medicine. Although the Immune system defense dfense neutrophils " neutrophilia " is similar to that seen during bacterial infections, Immune system defense Immuje the Sgstem population returns to normal by around 24 hours. Lymphatic vessels — Once filtration is complete, lymph vessels carry this fluid toward the heart. Common environmental allergens inducing IgE-mediated allergies include pet e. The constant flushing of the urinary tract and the bowel also helps. Each contains a constant region and a variable region. Biochemical Society Transactions. |
| Definition | Immune system defense A-3 Immune system defense contact of a new Sports nutrition experts antigen with sgstem naive Deffnse initiates the cognitive phase. The development of Immune system defense immunity is aided by the actions of the innate immune system, and is critical when innate immunity is ineffective in eliminating infectious agents. Current Pharmaceutical Design. Because only the cells that match the germ multiply, the immune response is customized. Cells infected by a virus may exhibit viral peptide antigens linked to surface Class I molecules. Next Steps Contact Us. |
| Immune Defense | Hypersensitivity or Allergic Reactions When immune responses are inappropriate or exaggerated and lead to tissue damage, the terms "hypersensitivity" or "allergy" are used. Nonspecific active defensive measures include a diverse variety of physiological responses for example, elevated body temperatures tachycardia, vomiting and diarrhea, pituitary-adrenal activation , phagocytic cell activation, creation of inflammatory reactions, formation of nitric oxide from arginine, and a stereotyped pattern of acute-phase reactions including fever, myalgias, arthralgias, headache and somnolence, anorexia, and a markedly altered pattern of protein synthesis and breakdown in liver and muscle, respectively. October You may be wondering, then, why does our immune system allow these bacteria to be around at all? The Th2 response is characterized by the release of cytokines IL-4, 5 and 13 which are involved in the development of immunoglobulin E IgE antibody-producing B cells, as well as the development and recruitment of mast cells and eosinophils that are essential for effective responses against many parasites. Like other 'unconventional' T cell subsets bearing invariant TCRs, such as CD1d -restricted natural killer T cells , γδ T cells straddle the border between innate and adaptive immunity. Our skin also tends to be dry and tough making it difficult for pathogens to gain entry. |
| The innate immune system: Fast and general effectiveness | During inflammation, the blood supply increases, helping carry immune cells to the affected area. Because of the increased blood flow, an infected area near the surface of the body becomes red and warm. The walls of blood vessels become more porous, allowing fluid and white blood cells to pass into the affected tissue. The increase in fluid causes the inflamed tissue to swell. The white blood cells attack the invading microorganisms and release substances that continue the process of inflammation. Other substances trigger clotting in the tiny vessels capillaries in the inflamed area, which delays the spread of the infecting microorganisms and their toxins. Many of the substances produced during inflammation stimulate the nerves, causing pain. Reactions to the substances released during inflammation include the chills, fever, and muscle aches that commonly accompany infection. When an infection develops, the immune system Overview of the Immune System The immune system is designed to defend the body against foreign or dangerous invaders. read more also responds by producing several substances and agents that are designed to attack the specific invading microorganisms see Acquired Immunity Acquired Immunity One of the body's lines of defense immune system involves white blood cells leukocytes that travel through the bloodstream and into tissues, searching for and attacking microorganisms and Examples are. Killer T cells T cells a type of white blood cell that can recognize and kill the invading microorganism. Antibodies Antibodies One of the body's lines of defense immune system involves white blood cells leukocytes that travel through the bloodstream and into tissues, searching for and attacking microorganisms and read more that target the specific invading microorganism. Antibodies attach to and immobilize microorganisms. They kill them outright or help neutrophils target and kill them. How well the immune system defends the body against each microorganism depends partly on a person's genetic make-up. Body temperature increases as a protective response to infection and injury. An elevated body temperature fever Fever in Adults Fever is an elevated body temperature that occurs when the body's thermostat located in the hypothalamus in the brain resets at a higher temperature, primarily in response to an infection A part of the brain called the hypothalamus controls body temperature. Fever results from an actual resetting of the hypothalamus's thermostat. The body raises its temperature to a higher level by moving shunting blood from the skin surface to the interior of the body, thus reducing heat loss. Shivering chills may occur to increase heat production through muscle contraction. The body's efforts to conserve and produce heat continue until blood reaches the hypothalamus at the new, higher temperature. The new, higher temperature is then maintained. Later, when the thermostat is reset to its normal level, the body eliminates excess heat through sweating and shunting of blood to the skin. Certain people such as the very old, the very young, and people with an alcohol use disorder are less able to generate a fever. These people may experience a drop in temperature in response to severe infection. Learn more about the Merck Manuals and our commitment to Global Medical Knowledge. Brought to you by About Merck Merck Careers Research Worldwide. Disclaimer Privacy Terms of use Contact Us Veterinary Edition. IN THIS TOPIC. OTHER TOPICS IN THIS CHAPTER. Defenses Against Infection By Larry M. Bush , MD, FACP, Charles E. Natural Barriers Against Infection The Blood Inflammation Immune Response Fever. Wall off the area. The lymphatic system forms a network similar to the blood vessels. It carries a substance called lymph instead of blood. Lymph is a fluid that carries immune-related cells to areas that need them. White blood cells are constantly looking for pathogens. When they find one, they begin to multiply and send signals to other cell types to do the same. What does a high white blood cell count mean? The immune system needs to be able to distinguish healthy from unhealthy cells and tissue to work effectively. It does this by recognizing signals called DAMPS — danger-associated molecular patterns. In many cases, an antigen is a bacterium, fungus, virus, toxin, or foreign body. But it can also be a cell that is faulty or dead. The immune system detects pathogen-associated molecular patterns — PAMPs — in the antigen. In this way, various parts of the system recognize the antigen as an invader and launch an attack. What is an antigen test? These cells surround and absorb pathogens and break them down, effectively eating them. There are several types, including :. Lymphocytes help the body remember previous invaders and recognize them if they return to attack again. Lymphocytes begin their life in bone marrow. Some stay in the marrow and develop into B lymphocytes B cells ; others travel to the thymus and become T lymphocytes T cells. These two cell types have different roles. B lymphocytes produce antibodies and help alert the T lymphocytes. T lymphocytes destroy compromised cells in the body and help to alert other leukocytes. Natural killer NK cells are also lymphocytes. NK cells recognize and destroy cells that contain a virus. What do low lymphocyte levels mean? Once B lymphocytes spot the antigen antibody generators , they begin secreting antibodies. Antibodies are special proteins that lock on to specific antigens. Each B cell makes one specific antibody. For instance, one might make an antibody against the bacteria that cause pneumonia , and another might recognize the common cold virus. Antibodies are part of a large family of chemicals called immunoglobulins, which play many roles in the immune response:. Antibodies lock on to the antigen but do not kill it — they only mark it for death. The killing is the job of other cells, such as phagocytes. There are distinct types of T lymphocytes, or T cells. Helper T cells Th cells coordinate the immune response. Some communicate with other cells, and some stimulate B cells to produce more antibodies. Others attract more T cells or cell-eating phagocytes. Killer T cells cytotoxic T lymphocytes attack other cells. They are particularly useful for fighting viruses. They work by recognizing small parts of the virus on the outside of infected cells and destroying the infected cells. Also a type of lymphocyte, these contain granules with powerful chemicals. They are useful for attacking many types of unwanted cells. Overall, the immune system becomes stronger on exposure to different pathogens. By adulthood, most people have had exposure to a range of pathogens and developed more immunity. Once the body produces an antibody, it keeps a copy so that if the same antigen appears again, the body can deal with it more quickly. Some diseases, such as measles, can be severe if they occur, which is why experts recommend vaccination. If a person has the measles vaccine, they are unlikely to get the disease. Once a pathogen is detected, nearby lymph nodes, often referred to as draining lymph nodes, become hives of activity, where cell activation, chemical signaling, and expansion of the number of immune system cells occur. The result is that the nodes increase in size and the surrounding areas may become tender as the enlarged nodes take up more space than usual. But, the same thing can occur anywhere lymph nodes are activated. The spleen is the largest internal organ of the immune system, and as such, it contains a large number of immune system cells. Indeed, about 25 percent of the blood that comes from the heart flows through the spleen on every beat. As blood circulates through the spleen, it is filtered to detect pathogens. As pathogens are detected, immune system cells are activated and increase in number to neutralize the pathogen. The spleen is particularly important in protecting people from bacterial infections, such as meningococcus and pneumococcus. So, while people can live without a spleen, it is important for them to be up to date on vaccines that protect against these infections because they are at greater risk of suffering from them. Sometimes the skin is described as the largest organ of the immune system because it covers the entire body. People may not think about the skin as being part of this system, but the reality is that skin serves as an important physical barrier from many of the disease-causing agents that we come into contact with on a daily basis. The innate immune system is the first line of defense against pathogens. In our example, the innate immune system is like the cops that patrol local beats. They take care of most of the criminal activity that takes place in a community and generally keep the peace. Similarly, most of the time our innate immune system effectively wards off infections by keeping pathogens in check. This is accomplished in several ways. Our bodies physically ward off many potential pathogens. As mentioned above, our skin is an important protective barrier. These cellular intersections are called tight junctions. Our skin also tends to be dry and tough making it difficult for pathogens to gain entry. Epithelial cells that line openings into our bodies, such as the nose and mouth as well as throughout the respiratory, digestive, and genital tracts, tend to have one or more additional protective features. First, the epithelial cells in these regions are coated with mucus, a thick, sticky solution that makes it difficult for pathogens to attach to them. Second, some of them also have microfibers, called cilia, which move the mucus and any pathogens in the mucus along the cell surface. Hairs in the nasal cavity work in a similar manner to trap pathogens in the air before they get into the lungs. Our bodies also use muscles to move air and liquids to keep pathogens from infecting us. Sneezing, watery eyes, vomiting and diarrhea are all examples of our innate immune system working to protect us. Mucus not only provides a physical barrier, it also contains chemicals that help protect us from pathogens. Epithelial cells also secrete chemicals that prevent infection. This is true of epithelial cells on our skin and in our digestive, respiratory, and genital tracts. Our body also uses chemical factors, such as acid, to create harsh environments for some pathogens. For example, the stomach has an acidic pH that makes it difficult for many viruses to survive the journey through the digestive tract. Bacteria live in and on us. As humans evolved, so did the bacteria that live on us. As a result, they are able to survive on our skin or in our digestive tract without our immune systems acting to rid them. For example, while Staphylococcus bacteria are generally harmless on our skin, if they enter our bodies, they can be troublesome. In some cases, the disturbance is minor, such as a pimple. In other cases, the result can be deadly, such as a bloodstream infection. You may be wondering, then, why does our immune system allow these bacteria to be around at all? Like with other things in life, the answer comes down to a risk-benefit ratio. When these bacteria are covering the surface of our skin or digestive tract, more harmful bacteria have less of an opportunity to do so. Additionally, commensal bacteria can help create conditions in the local environment that keep infectious agents from causing problems. For example, commensal bacteria may release chemicals that are toxic to other types of bacteria. Evidence for the importance of these bacteria can be seen after taking oral antibiotics. You may have loose stools or intestinal cramping for a few days. This is because antibiotics, such as penicillin, can kill many different types of bacteria — good and bad. A final way that the innate immune system works is through immune system cells. These cells are not specific in their search for invaders. The most important cells associated with innate immune responses are:. Watch this short video showing how the innate immune system works. When pathogens get past the non-specific mechanisms of protection afforded by the innate immune system, the adaptive immune system takes over. Memory cells monitor the body to stop or lessen the impact of future infections by the same pathogen. If a second infection occurs at all, it is typically shorter in duration and less severe than a first encounter. Vaccines allow us to leverage the advantages of immunologic memory without the risks involved with a first encounter. Sticking to our police force example, vaccines are like the practice drills that officers complete in an effort to be ready for an actual event. The adaptive immune response is driven by the activities of cells called antigen-presenting cells APCs. Three cell types can serve as APCs — dendritic cells, macrophages and B cells. Of these, dendritic cells are the most common and powerful APC type. They are considered to be the bridge between the innate and adaptive immune responses. Dendritic cells are produced in bone marrow and migrate through the blood to tissues where they monitor for pathogens. As this happens, the dendritic cell migrates from the tissue to the nearest lymph node where these surface signals, called antigens, help to activate T cells. Dendritic cells can process and present most types of pathogens, such as viruses, bacteria, fungi and parasites. Whereas antigen presentation is the primary function of dendritic cells, macrophages and B cells are capable APCs, but this is not their primary function. Macrophages, as described in the innate immune system section, primarily destroy pathogens, signal the innate immune response, and cause inflammation. When they function as APCs, it is typically to present antigens from pathogens they have ingested that have evolved so that they are not killed by typical innate immune responses. Similar to dendritic cells, macrophages and B cells, acting as APCs, must travel to the draining lymph node to activate the adaptive immune response. When antigen is presented in draining lymph nodes, the adaptive immune response starts in earnest. |
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