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Adaptive immune system – (or acquired immune system): A subsystem of the immune system that is made up of specialized, systemic cells which process and eliminate germs (e.g., bacteria and viruses) or prevent their growth. The adaptive immune system “remembers” germs, so the next time a known germ is encountered, it can respond faster (known as immunological memory). Antibodies are a critical part of the adaptive immune system. By specifically targeting the type of germ that is causing the infection, the adaptive immune system takes over if the innate immune system – the body’s first line of defence that doesn’t distinguish between different germs – is not able to destroy the germs. For this reason, the adaptive immune system is slower to respond than the innate immune system, but when it does, it is more accurate.
Cytokines – Cytokines are small proteins that control the growth and activity of other immune system cells and blood cells. When released, they signal to the immune system to do its job. Cytokines affect the growth of all blood cells and other cells that help the body’s immune and inflammation responses.
Dendritic cells – A type of immune cell that is found in tissues, such as the skin, that initiates immune responses by presenting antigens (foreign substances) on its surface to other cells of the immune system to activate them.
Innate immune system – A subsystem of the immune system that is the body’s first line of defense against germs that enter the body. It is sometimes referred to as the “nonspecific” immune system because it responds in the same way to all germs and foreign substances. The innate immune system responds quickly but it has only limited ability to stop germs from spreading. The adaptive immune system takes over if the innate immune system is not able to destroy the germs by specifically targeting the type of germ that is causing the infection. For this reason, the adaptive immune system is slower to respond than the innate immune system, but when it does it is more accurate.

Keratinocytes – The primary type of cell found in the epidermis, the outermost layer of the skin.

Lymphocyte – A type of white blood cell that is part of the immune system. There are two main types of lymphocytes: B cells and T cells.
Macrophage – A type of white blood cell that destroys bacteria and other harmful substances and stimulates the action of other immune system cells. Monocyte – a type of leukocyte, or white blood cell. They can differentiate into macrophages and conventional dendritic cells and, as a part of the innate immune system, monocytes also influence the process of adaptive immunity.
Neutrophil – A type of immune cell that is one of the first cell types to travel to the site of an infection.

Osteoblast – Cells that form new bone. They also come from the bone marrow and are related to structural cells.

Osteoclast – A large bone cell which absorbs bone tissue during growth and healing.

Osteoprogenitor – Cells located in the bone that play a role in bone repair and growth. These cells are the precursors to the more specialized bone cells (osteocytes and osteoblasts) and reside in the bone marrow.

Synoviocyte – A cell that lines the inner surface of joints and tendon sheaths.

T cells – (also called T lymphocyte): A type of white blood cell that is an essential part of the immune system. T cells are one of two primary types of lymphocytes–B cells being the other–that initiate immune response to antigens (foreign substances) in the body.

T helper cells (Th cells) – A type of T cell that play an important role in the immune system, particularly in the adaptive immune system. When stimulated by a specific antigen (foreign substance) they “help” the activity of other immune cells by releasing cytokines, small protein mediators that alter the behavior of target cells that in turn, express receptors for those cytokines. Subsets of Thcells (e.g., Th1, Th17) produce different cytokines.

Definitions references adapted from: https://medical-dictionary.thefreedictionary.com and https://www.britannica.com.

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