Immune Response: The Good, The Bad, The ControlledThe immune system protects the body from disease. Over the past decade, however, researchers have come to understand that the innate immune system — the part of the immune system that serves as the body’s first line of defense — is implicated in an enormous number of disease processes that affect many millions of people around the world. Show
Sometimes the immune system runs too hot, erroneously attacking the body. Sometimes, it runs too cold — its defenses insufficient to defend against invaders. We now know that the tipping point between running too hot or too cold often depends on the innate immune response, but we don’t know how to prevent it from going off course. The CIIID’s goal is to determine how to fine-tune the innate immune system (so that it knows exactly when to turn on and how to protect the body), and then how to turn it off before it causes any collateral damage. The Two Halves of the Immune SystemManipulating immune function — enhancing it or suppressing it — will rest on our ability to control the two aspects of the immune system: innate immunity, mentioned above, and adaptive immunity. The innate immune system: the first line of defense The innate immune system is the first part of the body to detect invaders such as viruses, bacteria, parasites and toxins, or to sense wounds or trauma. Upon detection of these agents or events, the innate immune system activates cells to attack and destroy the outsider, or to initiate repair, while also informing and modulating the adaptive immune response that follows this first line of defense. The adaptive immune system: the second, specific response Adaptive immune cells are the second and specific line of defense, and they are called to action by the innate immune system. After recognizing the invader, the cells can multiply and combat it, leading to recovery from disease and protection against its return. Harnessing the Innate Immune SystemThe idea of using the immune system to help the body fight disease has been in existence for some time; vaccines, which allow the body to remember disease-causing pathogens, provide an excellent example. There are many diseases, though, in which the desired outcome is not to enhance the immune system, but to suppress its unwanted effects. Lupus, rheumatoid arthritis and multiple sclerosis, for instance, are autoimmune diseases in which the immune system erroneously attacks the body. Chronic inflammation, connected with wound trauma, diabetes, cardiovascular disease and neurodegenerative disease, is another example of immune-system overreaction. The idea of using innate immunity to either enhance or suppress overall immunity is a new avenue by which we can have profound impact on improving human health. In striving to understand the innate immune system, the CIIID’s ultimate goal is to regulate overall immune response to distinct disease processes, thus using the power of immunity to improve human health. In doing so, we will improve the body’s ability to fight pathogens and to control the immune response when it goes off track — and we will change medicine forever. The immune system is the body’s tool for preventing or limiting infection. Without it, the body would be unable to withstand attacks from bacteria, viruses, parasites, and more. The immune system consists of a vast network of cells, organs, proteins, and tissues throughout the body. A fully functional immune system can distinguish healthy tissue from unwanted substances. If it detects an unwanted substance, it will mount an immune response — a complex attack to protect the body from invaders. It also recognizes and removes dead and faulty cells. The immune system does not always get it right, however. Sometimes, for instance, it is unable to fight effectively because a person has a health condition or needs certain medications that affect how the system works. In autoimmune diseases and allergies, the immune system mistakenly perceives healthy tissue as unhealthy and launches an unnecessary attack, leading to uncomfortable and sometimes dangerous symptoms. This article will look at some of the main features of the immune system and how they defend the body from pathogens and other invaders. It will also look at problems that can arise with the immune system. The immune system consists of a range of components, including:
White blood cells circulate in the blood and lymphatic vessels. 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. The body stores white blood cells in different places, known as lymphoid organs. These include:
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. Cell damage may be present for many reasons, including:
An antigen is any substance that can spark an immune response. 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? There are two main types of leukocytes, or white blood cells: 1. PhagocytesThese cells surround and absorb pathogens and break them down, effectively eating them. There are several types, including:
2. LymphocytesLymphocytes 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? The role of B lymphocytesOnce 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. The role of T lymphocytesThere 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. The role of natural killer cellsAlso 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. If an unvaccinated person has measles once, it is also rare to get it again. In both cases, the body stores a measles antibody. The antibody is ready to destroy the virus next time it appears. This is called immunity. There are three types of immunity in humans:
Innate immunityPeople are born with some level of immunity that will attack invaders from day one. This innate immunity includes the external barriers of our body — the first line of defense against pathogens — such as the skin and mucous membranes of the throat and gut. This response is general and nonspecific. If pathogens manage to bypass the innate immune system, macrophages will attack them. Macrophages will also produce substances called cytokines, which increase the inflammatory response. Adaptive (acquired) immunityA person’s protection from pathogens develops as they go through life. Thanks to vaccinations and exposure to various diseases, the body develops a range of antibodies to different pathogens. Doctors sometimes refer to this as immunological memory because the immune system remembers previous enemies. Passive immunityThis is a temporary type of immunity that derives from another person. For instance, a newborn receives antibodies from the mother through the placenta before delivery and in breast milk following delivery. This passive immunity protects the infant from some infections during their early life. There are many ways in which the immune system can go wrong. Types of immune disorders fall into three categories: ImmunodeficienciesThese arise when one or more parts of the immune system do not function. They can result from:
These conditions can increase a person’s risk of becoming sick or experiencing severe symptoms, as the COVID-19 pandemic has shown. What are examples of immunodeficiency disorders? AutoimmunityIn autoimmune conditions, the immune system mistakenly targets healthy cells rather than pathogens or faulty cells. It is unable to distinguish between healthy and unhealthy cells and tissue. Usually, this will occur in one part of the body, such as the pancreas. Destruction of pancreatic beta cells means the body cannot produce insulin. This is how type 1 diabetes happens. Other autoimmune diseases include:
HypersensitivityWith hypersensitivity, the immune system reacts in an exaggerated or inappropriate way. It attacks everyday substances, such as dust, as if they were pathogens. This happens with:
A severe reaction can lead to anaphylactic shock, where the body responds to an allergen so strongly that it can be life threatening. Here are some answers to questions people often ask about immunity. How can I improve my immunity?Tips for boosting immunity include:
Find out which foods can boost the immune system here What types of immunity are there?Innate immunity refers to the defenses people are born with, including the skin, mucous membranes, and various components of the immune system. Acquired immunity comes from vaccines and exposure to diseases. These enable the body to develop antigens that can help it fight the same disease a second time. Passive immunity is protection that comes from another person, for example, when a newborn is temporarily immune to certain diseases because their mother has immunity. Why is immunity important?Immunity protects the body from bacteria, viruses, and other pathogens that could lead to life threatening diseases. The immune system is a complex system that is vital for survival. When the body faces harmful invaders, such as a virus or a splinter in the finger, it launches an attack to destroy the pathogens. People are born with some types of immunity, but exposure to diseases and vaccinations can also help boost the body’s defenses. Some people have a weakened immune system because of a health issue or medication use. A doctor can advise on how to protect a person’s health when living with a weakened immune system. Ways of boosting immunity include dietary and exercise choices, avoiding alcohol and smoking, and having appropriate vaccinations. |
System that fights disease and controls the immune response
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