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The activation of T H 1 and M1 macrophage is a positive feedback loop, with IFN-γ from T H 1 cells upregulating CD40 expression on macrophages; the interaction between CD40 on the macrophages and CD40L on T cells activate macrophages to secrete IL-12; and IL-12 promotes more IFN-γ secretion from T H 1 cells.
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 ...
Macrophages are diffusely scattered in the connective tissue and in liver (Kupffer cells), spleen and lymph nodes (sinus histiocytes), lungs (alveolar macrophages), and central nervous system (microglia). The half-life of blood monocytes is about 1 day, whereas the life span of tissue macrophages is several months or years.
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.
The T cell zone (periarteriolar sheath) and B cell follicles contain discrete macrophage populations; however, not much is known about these macrophage populations in terms of their origin and lifespan. These macrophages are not unique to the spleen but instead make up an integral part of the lymphoid parts of all secondary lymphoid organs.
Mature macrophages do not travel far from the site of infection, but dendritic cells can reach the body's lymph nodes, where there are millions of lymphocytes. [59] This enhances immunity because the lymphocytes respond to the antigens presented by the dendritic cells just as they would at the site of the original infection. [ 60 ]
T helper cells (T H cells) assist other lymphocytes, including the maturation of B cells into plasma cells and memory B cells, and activation of cytotoxic T cells and macrophages. These cells are also known as CD4 + T cells as they express the CD4 glycoprotein on their surfaces.
The main effector cells of T h 1 immunity are macrophages as well as CD8 T cells, IgG B cells, and IFN-γ CD4 T cells. The key T h 1 transcription factors are STAT4 and T-bet. IFN-γ secreted by CD4 T cells can activate macrophages to phagocytose and digest intracellular bacteria and protozoa.