Eleanor Finch
The immune system is a complex network of organs, cells, and proteins that defends the body against infection while protecting the body's own cells. It is comprised of two divisions: the innate (general) immune system and the adaptive (specialized) immune system. The innate immune system acts as the body's first line of defense, responding rapidly and non-specifically to all germs and foreign substances. On the other hand, the adaptive immune system specifically targets the type of germ causing the infection, allowing it to adapt to new types of infections and remember germs to fight them faster in the future. These two systems work closely together, utilizing various cells, proteins, and bodily mechanisms to protect the body from harm.
| Characteristics | Innate Immune System | Adaptive Immune System |
|---|---|---|
| First line of defence | Yes | No |
| Response time | Quick | Slow |
| Accuracy | Low | High |
| Memory | No | Yes |
| Cell types | Natural killer cells, neutrophils, monocytes, phagocytes | B cells, T cells |
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What You'll Learn
The innate immune system
The immune system is made up of two divisions: the innate (general) immune system and the adaptive (specialized) immune system. The innate immune system is the body's first line of defence against intruders and acts very quickly. It responds in the same way to all germs and foreign substances, which is why it is sometimes referred to as the "non-specific" immune system.
If germs manage to get past these initial barriers and enter the body, the innate immune system fights them using special immune system cells and proteins. For example, bacteria or viruses that enter the body can be stopped by phagocytes, a type of white blood cell that encloses and "digests" germs, making them harmless. Natural killer cells, another type of innate leukocyte, identify and destroy cells that have been infected by a virus or abnormal cells that may turn into tumour cells.
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The adaptive immune system
The immune system is composed of two divisions: the innate (general) immune system and the adaptive (specialized) immune system. The adaptive immune system is slower to respond than the innate immune system but is more accurate when it does. It has the advantage of being able to "'remember'" germs, so the next time it encounters a familiar germ, it can fight it faster.
B cells produce antibodies, also known as immunoglobulins. There are five major classes of antibodies: IgG, IgA, IgM, IgD, and IgE. IgG is the major immunoglobulin class in the body and is found in the bloodstream and tissues. IgA is composed of two IgA molecules joined by a J-chain and attached to a secretory piece, which allows it to be secreted into mucus, intestines, and tears, where it protects against infection. IgM is composed of five immunoglobulin molecules attached to each other and is formed early in infection.
T cells, or T-lymphocytes, are white blood cells produced in the thymus and lymph nodes. They are also known as memory cells because they keep a record of every germ the body has defeated, allowing them to recognize and destroy the microbe quickly if it enters the body again.
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Germ recognition
The immune system is a complex network of organs, cells, and proteins that defends the body against infection while protecting the body's own cells. It is made up of the innate (general) immune system and the adaptive (specialized) immune system. These two systems work closely together but perform different tasks.
The innate immune system is the body's first line of defense against foreign invaders. It responds in the same way to all germs and foreign substances, which is why it is sometimes referred to as the "non-specific" immune system. It acts very quickly to detect and destroy bacteria that have entered the body through the skin or mucous membranes. Substances like acid, enzymes, and mucus also help prevent bacteria and viruses from growing, and certain movements in the body, such as coughing, prevent germs from settling.
The innate immune system includes neutrophils, monocytes, natural killer cells, and complement proteins. Natural killer cells identify and destroy cells infected by a virus or abnormal cells that may turn into tumor cells. Phagocytes, a type of white blood cell, enclose and "digest" bacteria or viruses, making them harmless.
However, the innate immune system cannot always stop germs from spreading. If it fails to destroy the germs, the adaptive immune system takes over. This system specifically targets the type of germ causing the infection, but it needs to recognize the germ first, which makes it slower to respond than the innate immune system.
The adaptive immune system includes B cells and T cells, which are types of lymphocytes, a specific kind of white blood cell. These cells require training to learn how to fight invaders (antigens) and not attack the body's own cells. Antibodies, also known as immunoglobulins, are produced by B cells and help the body fight microbes or the toxins they produce. There are five major classes of antibodies (IgG, IgA, IgM, IgD, and IgE), each with distinct functions. For example, IgA is produced near mucus membranes and protects the respiratory tract and intestines from infection. IgG is the major immunoglobulin class in the body and is found in the bloodstream, tissues, and secretions.
Lymph nodes are part of the immune system and send out lymphocytes to fight infection. These lymphocytes travel through the lymphatic vessels and bloodstream to different areas of the body. The spleen, a blood-filtering organ, also plays a role in the immune system by removing microbes and producing antibodies and lymphocytes.
Overall, the immune system's ability to recognize and remember germs is crucial for its effectiveness in defending the body against infection.
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Immune system cells
The immune system is composed of a variety of different cell types and proteins, each with a specific task aimed at recognizing and reacting against foreign material (germs). The immune system is divided into two parts: the innate (general) immune system and the adaptive (specialized) immune system.
Innate Immune System Cells
The innate immune system is the body's first line of defence against intruders. It responds in the same way to all germs and foreign substances, acting very quickly. The innate immune system includes neutrophils, monocytes, natural killer (NK) cells, and a set of proteins known as complement proteins.
Neutrophils are the most numerous and important cellular component of the innate immune response. They are phagocytes, which are white blood cells (leukocytes) that enclose and "digest" germs, making them harmless. Monocytes are another type of white blood cell that circulates in the blood and differentiates into macrophages upon migration into the tissues.
Natural killer cells are large granular lymphocyte-like cells that lack antigen-specific receptors. They are able to recognize and kill abnormal cells, such as tumor cells and virus-infected cells, using substances called cytotoxins.
Adaptive Immune System Cells
The adaptive immune system specifically targets the type of germ causing an infection, but it first needs to recognize it, which is why it is slower to respond than the innate immune system. However, it has the advantage of being able to "remember" germs, so it can respond faster during subsequent encounters.
The adaptive immune system includes B cells and T cells, which are the two major groups of lymphocytes (a type of white blood cell) that recognize and attack germs. B cells produce antibodies, providing long-lasting immunity to specific infections. Similarly, T cells can remember viruses the body has encountered and mount a more vigorous response when they encounter the same virus again.
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Immune disorders
The immune system is the body's defence mechanism against harmful invaders such as bacteria, viruses, toxins, cancer cells, and foreign substances. It is made up of two divisions: the innate (general) immune system and the adaptive (specialized) immune system. When the immune system doesn't function properly, it results in immune disorders, which can be classified into two main types: primary immune deficiency and acquired immune deficiency.
Primary Immune Deficiency
Primary immune deficiency, also known as congenital immune deficiency, is a condition where an individual is born with a weak immune system. Severe combined immunodeficiency (SCID), commonly known as "bubble boy disease," is an example of a primary immune deficiency disorder. Children with SCID lack important white blood cells and are highly susceptible to constant infections from bacteria, viruses, and fungi.
Acquired Immune Deficiency
Acquired immune deficiency is a condition where an individual's immune system weakens due to various factors. Certain medications, such as chemotherapy drugs or immunosuppressants used after organ transplants, can suppress the immune system. Infections like the flu, mononucleosis, and measles can also temporarily weaken the immune response. Lifestyle factors, including smoking, alcohol consumption, and poor nutrition, can contribute to acquired immune deficiency. HIV, which causes AIDS, is an example of an acquired viral infection that destroys white blood cells and severely compromises the immune system.
Autoimmune Disorders
Autoimmune disorders occur when the body's immune system mistakenly attacks and destroys its own healthy tissues and organs. There are more than 80 recognised autoimmune disorders, including rheumatoid arthritis, multiple sclerosis, lupus, type 1 diabetes, and Hashimoto's disease. While the exact causes of autoimmune disorders are unknown, a combination of genetic factors and environmental triggers, such as certain medications or infections, are believed to play a role. Treatment options for autoimmune disorders aim to control the abnormal immune response and manage symptoms, often involving immunosuppressive medications like corticosteroids.
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Frequently asked questions
The immune system is made up of the innate (general) immune system and the adaptive (specialized) immune system.
The innate immune system is the body's first line of defence against foreign substances. It acts quickly and responds in the same way to all germs, destroying them on the spot. It includes neutrophils, monocytes, natural killer cells, and complement proteins.
The adaptive immune system takes over when the innate immune system fails to stop the spread of germs. It specifically targets the type of germ causing the infection and has the ability to remember" germs to fight them faster in the future. It involves T cells and B cells, which require training to learn how to fight invaders and not attack the body's own cells.
