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A lymphocyte is a type of white blood cell (leukocyte) in the immune system of most vertebrates. [1] Lymphocytes include T cells (for cell-mediated and cytotoxic adaptive immunity), B cells (for humoral, antibody-driven adaptive immunity), [2] [3] and innate lymphoid cells (ILCs; "innate T cell-like" cells involved in mucosal immunity and homeostasis), of which natural killer cells are an ...
T cells can be distinguished from other lymphocytes by the presence of a T-cell receptor (TCR) on their cell surface. T cells are born from hematopoietic stem cells, [1] found in the bone marrow. Developing T cells then migrate to the thymus gland to develop (or mature). T cells derive their name from the thymus.
The secondary (or peripheral) lymphoid organs, which include lymph nodes and the spleen, maintain mature naive lymphocytes and initiate an adaptive immune response. [15] The secondary lymphoid organs are the sites of lymphocyte activation by antigens. [16] Activation leads to clonal expansion, and affinity maturation. Mature lymphocytes ...
Within the thymus, thymus cell lymphocytes or T cells mature. T cells are critical to the adaptive immune system, where the body adapts to specific foreign invaders. The thymus is located in the upper front part of the chest, in the anterior superior mediastinum, behind the sternum, and in front of the heart. It is made up of two lobes, each ...
Lymphocyte: 30%: Small lymphocytes 7–8 Large lymphocytes 12–15: B cells: releases antibodies and assists activation of T cells; T cells: CD4+ T helper cells: activate and regulate T and B cells; CD8+ cytotoxic T cells: virus-infected and tumor cells. Gamma delta T cells: bridge between innate and adaptive immune responses; phagocytosis
Although lymphocytes are usually considered mature, as seen in blood tests, they are certainly not inert. Lymphocytes can travel around the body wherever there is a need. When such needs arise, new rounds of downstream lymphopoiesis, such as cell multiplication and differentiation, may occur, accompanied by intense mitotic and metabolic activity.
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Through elimination of autoreactive lymphocytes, tolerance ensures that the immune system does not attack self peptides. [2] Lymphocyte maturation (and central tolerance) occurs in primary lymphoid organs such as the bone marrow and the thymus. In mammals, B cells mature in the bone marrow and T cells mature in the thymus. [1]