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Innate immunity and adaptive immunity are two types of immune responses that help to protect the body against infections and other harmful substances.
Innate immunity is the body’s first line of defense against infections and other harmful substances. It is the body’s natural, nonspecific immune response, and it is activated immediately upon encountering a pathogen or other foreign substance. Innate immunity includes physical and chemical barriers, such as the skin and mucous membranes, as well as immune cells, such as neutrophils and macrophages.
Adaptive immunity, also known as acquired immunity, is a more specific and slower-acting immune response that is activated after the body has been exposed to a pathogen or other foreign substance. Adaptive immunity involves activating T cells and B cells, which recognize and attack specific pathogens or other foreign substances. Adaptive immunity also includes the production of antibodies, which are proteins that specifically target and neutralize pathogens or other foreign substances.
In summary, innate immunity is a nonspecific, immediate immune response that provides the body’s first line of defense against infections and other harmful substances. Adaptive immunity is a specific, slower-acting immune response that is activated after the body has been exposed to a pathogen or other foreign substance, and it involves the activation of T cells and B cells and the production of antibodies.
The immune system defends the host (you) against pathogens such as bacteria, fungi, viruses, and protists. Specific types of these organisms cause disease in humans. The immune system must be able to detect pathogens, distinguish them from host cells, and get rid of them. The immune system also detects cancerous and damaged cells. To accomplish this, the immune system has two layers of defenses: the innate and adaptive immune systems.
Your body cells have surface proteins on them that are part of a complex called the major histocompatibility complex. These proteins are like flags on the surface of your cells that tell your immune system that these are “self” cells, not invaders. When your immune system inadvertently attacks “self” cells, it is autoimmunity.
The innate immune system is a fast, nonspecific, but temporary immune response that can be divided into barrier, chemical, and cellular defenses. When a known pathogen invades, the innate immune system starts sluggishly from scratch each time.1
Mechanical barriers physically prevent pathogens from entering the body. The innate immune system provides the first line of defense against invading pathogens. It includes a number of physical, chemical, and biological barriers that prevent pathogens from entering the body or spreading throughout the body. Some of the key barrier defenses in the innate immune system include:
If pathogens breach the barrier defenses, they will trigger an inflammatory response. Inflammation is triggered by chemicals released by injured or infected cells. These chemicals cause increased blood flow and leakiness in blood vessels and direct infection-fighting cells to the infected area.
The signs and symptoms of inflammation include the following:
The complement system is a complex system that, when activated, coat pathogen surfaces with protein fragments, targeting them for destruction.
Innate immune cells are phagocytes (commonly thought of as the Pac-men of the immune system). They engulf and digest pathogens. Some phagocytes patrol throughout the body, and some reside in specific tissues. Digestive enzymes and acids located in vesicles in the phagocyte will kill and digest the pathogen.
White blood cells called leukocytes serve many functions in the innate immune system.
The innate response is the more primitive of the two branches of the immune response. The imprecise and sluggish targeting by the innate immune system can wreak havoc on your body’s tissues.1 The adaptive immune system provides a more controlled response.
The adaptive immune system consists of specialized cells and processes targeting specific pathogens. The adaptive immune system is designed to recognize and remember specific pathogens so follow-up responses can be faster, stronger, and more comprehensive.
Cells in the adaptive immune system are lymphocytes. The two main types of lymphocytes are T cells and B cells. T cells destroy infected cells and release chemicals that regulate the immune system. B cells secrete antibodies that bind with antigens on pathogens to mark them so they are easier for other immune cells to remove. Each lymphocyte expresses one or at most a few receptor types, which means that only pertinent lymphocytes are activated, and they detect the slightest distinction between self and non-self cells.1
There are multiple types of T cells. The two major classes are helper T cells and cytotoxic T cells. After a macrophage phagocytizes a pathogen, a part of the pathogen is displayed on the macrophage’s surface as a flag. These cells are called antigen-presenting cells and play an important role in activating T cells.
CD4+ T cells are also known as T helper cells. They are activated by dendritic cells, which present antigens (proteins on the surface of pathogens) to them. Once activated, CD4+ T cells secrete cytokines (small proteins that help to coordinate the immune response) and help to activate other immune cells, such as B cells and macrophages. Once helper T cells are activated, they help direct the innate and adaptive immune systems.
CD8+ T cells or killer T cells (cytotoxic T cells) destroy cells that have non-self-antigens on their surface. They recognize and kill cancerous or infected cells by releasing toxic chemicals, such as perforin and granzymes.
Regulatory T cells help regulate the immune response and prevent autoimmune diseases, which are conditions in which the immune system attacks healthy cells in the body.
B cells create antibodies, which are large, Y-shaped proteins that identify and neutralize foreign invaders. B-cells may also serve as antigen-presenting cells and secrete chemicals.
B cells must be activated first. This occurs when the B cell engulfs and digests an antigen. The antigen may be free-floating or on the pathogen. B cells internalize the antigen and present it to helper T cells. The helper T cells then secrete cytokines that stimulate B cells to multiply and produce plasma cells and memory B cells. Plasma B cells produce antibodies. Antibodies binding to antigens make it easier for phagocytic cells to find and destroy them. Memory B cells remain in the body after an infection and can provide long-lasting immunity by producing large amounts of antibodies if the same pathogen is encountered a second time.
Upon encountering antigens displayed on a pathogen they recognize, lymphocytes proliferate extensively to maximize their fighting power and differentiate into subsets of cells to allow for an even better-targeted response.
The lymphatic system includes organs such as the thymus, spleen, hundreds of lymph nodes, and the lymphatic vessels connecting them. These organs provide a haven for lymphocytes to be produced, undergo a complicated maturation process, and reside until they are ready to fight infections.
B cells mature in the bone marrow and then enter the lymphatic system to search for pathogens. T cells mature in the thymus. Bone marrow and the thymus are primary lymphoid organs because the lymphocytes mature there.
The tonsils, spleen, and lymph nodes are secondary lymphoid organs. They store lymphocytes and filter lymph. It is in secondary lymphoid organs that lymphocytes encounter pathogens, which activate them and initiate their adaptive responses. Chemicals secreted by immune cells, known as chemokines and adhesion molecules, bring immune cells together at the right time and place.2
Innate immunity and adaptive immunity are two types of immune responses that help to protect the body against infections and other harmful substances. The main difference between the two is the nature of the immune response and the speed at which it is activated.
Both types of immunity are essential and are linked in their processes. The phagocytic cells in the innate immune system capture pathogens, cut them up into small molecular pieces of proteins, and present these antigens to the lymphocytes. These antigen-presenting cells link innate and adaptive immunity.
Aging is associated with several changes in the immune system that can affect its function and increase the risk of infections and autoimmune diseases. This decline in immune function is called immunosenescence. Some of the key ways in which aging affects the immune system include:3,4
Overall, aging is associated with many changes in the immune system that can affect its function and increase the risk of infections and chronic diseases. However, there are ways to help maintain a healthy immune system, such as eating a balanced diet, getting regular exercise, and getting enough sleep.
Your immune system is a complex, hard-working system that protects you against pathogens. Any lifestyle changes you can make to reduce strain on your immune system may pay off with a decreased risk of chronic diseases due to low-grade inflammation or an increased risk of frequent infections. While scientific evidence does not support the premise that lifestyle changes can improve your immune system, optimizing your overall health is sure to allow your immune system to function at its full potential.
Consume a nutritious, balanced diet to provide your immune system with the vitamins and minerals it needs to function at its best. Choose from a wide array of fresh fruits and vegetables, whole grains, legumes, low-fat dairy products, and lean meats. Drink plenty of fluids.
Eat foods rich in5
Avoid consuming ultra-processed foods, excessive alcohol, refined sugar, salt, and saturated fats.
Activation of the immune system alters sleep, and sleep affects how well both arms of the immune system function. When you are sick, the immune system activates the inflammatory pathway, which can induce and increase sleep duration and intensity or disrupt sleep. Prolonged sleep deficiency can also induce chronic, systemic, low-grade inflammation, which is associated with many chronic diseases such as diabetes, atherosclerosis, cardiovascular disease, asthma, and neurodegeneration.6
Sleep is necessary to strengthen the immune response after vaccination, maintain overall immune health, fight pathogens and reduce the risk of complications from infections, and decrease the risk of chronic diseases associated with low-grade inflammation.6
Exercise and even movement throughout the day can improve overall health and support immune function. Exercising in moderation is the key. Overexertion for long periods can actually suppress immune function. Exercise can increase the circulation of immune cells, which can help them reach sites of infection more quickly and reduce inflammation.
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While we strive to always provide accurate, current, and safe advice in all of our articles and guides, it’s important to stress that they are no substitute for medical advice from a doctor or healthcare provider. You should always consult a practicing professional who can diagnose your specific case. The content we’ve included in this guide is merely meant to be informational and does not constitute medical advice.
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3. Fuentes E, Fuentes M, Alarcón M, Palomo I. Immune System Dysfunction in the Elderly. An Acad Bras Cienc. Jan-Mar 2017;89(1):285-299. doi:10.1590/0001-3765201720160487
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5. Philippou E, Negm A, Heyn PC. Ten Simple Dietary Steps to Strengthen Your Immune System – A Guide for Older Individuals at Risk of COVID-19. Arch Phys Med Rehabil. Sep 2021;102(9):1865-1868. doi:10.1016/j.apmr.2021.04.002
6. Besedovsky L, Lange T, Haack M. The Sleep-Immune Crosstalk in Health and Disease. Physiol Rev. Jul 1 2019;99(3):1325-1380. doi:10.1152/physrev.00010.2018