lymphoid system

Components of the lymphoid system are:
● immune cells – B cell lymphocytes and plasma cells, dendritic cells, granulocytes, macrophages, monocytes of mononuclear phagocyte system (MPS), T cell lymphocytes
● lymph ducts and vessels and lymph nodes (right)
[] histopathology []
● lymphoid organs including reticuloendothelial system – bone marrow, (lymph nodes), mucosa-associated lymphoid tissue, Peyer's patches, spleen, thymus, tonsils, vermiform appendix

The reticuloendothelial system or mononuclear phagocytic system comprises a range of cells that are capable of phagocytosis, including macrophages and monocytes. Phagocytosis is an innate immune process, and is not an adaptive immune process. The phagocytic cells either circulate in the blood or are attached to various connective tissues such as pulmonary alveoli, liver sinusoids, skin, spleen, and joints.

The RES functions to provide phagocytic cells for both the inflammatory response and immune responses (primary RES) and to remove pathogens and senescent cells from circulation (secondary RES)

The reticuloendothelial system (RES) includes:
● primary (central) lymphoid production organs – bone marrow, thymus
● secondary (peripheral) lymphoid function organs – circulating monocytes, histiocytes located in many tissues, Kupffer cells of the liver, "Littoral cells" of the spleen, mucosa-associated lymphoid tissue (MALT), which is subdivided into bronchus-associated lymphoid tissue (BALT) and gut-associated lymphoid tissue (GALT), Peyer's patches.

Tables  Fc receptors  Immune Cytokines  Immunoglobulins

o-o index of tissue micrographs [] germinal centers [] fluorescence microscopy dendritic cell uptake of dying cells within spleen [] micrograph red pulp of spleen [] micrograph splenic red pulp [] micrograph spleen cells (mouse) DAPK2 stained [] micrograph white pulp, splenic nodule [] micrograph white pulp infiltrate with Langhans giant cell [] histopathology spleen Gaucher's disease [] micrograph gallery cell surface antigens [] Virtual Histology Main []


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macrophages

Macrophages (and dendritic cells) are distributed in peripheral tissues where they eliminate invading foreign substances and are therefore responsible for innate immunity.

▼: acquired immunity : alveolar macrophages : APC : exudate macrophages : free and fixed macrophages : histiocytes : IL-1 : inflammatory macrophages : Kupffer's cells : Langerhans's cells : leukocyte immigration : life-span : mononuclear phagocyte system : MPS : normal macrophages : peritoneal, pleural macrophages : phagocytes : RES : reticulo-endothelial system : tissue renewal :▼

Macrophages are mature, tissue-differentiated monocytes of the reticulo-endothelial system (RES) or mononuclear phagocyte system (MPS). Since macrophages are derived exclusively from monocytes they exhibit similar properties. The term exudate macrophages designates the developmental stage and not the functional state. Inflammatory macrophages are found in exudates, where they may be characterized specific markers, such as peroxidase activity. Normal macrophages include macrophages located in tissues that include:
● connective tissue –histiocytes
● liver sinusoids – Kupffer's cells
● lung – alveolar macrophages
● lymph nodes – free and fixed macrophages
● spleen – free and fixed macrophages
● bone marrow – fixed macrophages
● serous fluids –pleural and peritoneal macrophages
● skin – histiocytes, Langerhans's cell

Macrophages trigger acquired immunity by capturing foreign (exogenous) antigens, which they ingest in cellular lysosomes. [im] Post-hydrolysis, the fragmented antigens are displayed on the cell surface together with macrophage proteins (APC). A number of C-type lectins are specifically expressed on macrophages and dendritic cells.

Coated with fragments of foreign antigens, macrophages migrate to secondary lymphoid organs, where they present the antigens to T lymphocytes. This process sensitizes the T cells to recognize antigens.

Macrophages are ubiquitously distributed mononuclear phagocytes responsible for numerous homeostatic, immunological, and inflammatory processes. Their wide tissue distribution enables them to provide an immediate defence against foreign elements prior to leukocyte immigration. Macrophages participate in both specific immunity via antigen presentation and in IL-1 production and nonspecific immunity against bacterial, viral, fungal, and neoplastic pathogens, so macrophages display a range of functional and morphological phenotypes. The life-span of macrophages ranges from 6 to 16 days. Under normal, steady-state conditions, tissue macrophages are renewed by local proliferation of progenitor cells rather than by monocyte influx into tissue, though invagination of monocytes does occur.

▲: acquired immunity : alveolar macrophages ф antibodies ф antigen : APC ф APCs ф B cells ф blood ф dendritic cells : exudate macrophages : free and fixed macrophages ф granulocytes ф hematopoiesis : histiocytes : IL-1 : inflammatory macrophages ф inflammatory response ф immune cytokines ф immune response : Kupffer's cells : Langerhans's cells : leukocyte immigration ф leukocytes : life-span ф leukocytes ф lymphocytes ф lymphokines ф lymphoid system ф migration ф monocytes : mononuclear phagocyte system : MPS : normal macrophages : peritoneal, pleural macrophages : phagocytes ф phagocyte ф receptors : RES : reticulo-endothelial system ф T cells : tissue renewal :▲

[] Macrophage in the process of surrounding tumor cell, artist's impression - cellular_macrophage [] sem Macrophage [] sem "walking macrophage" [] sem activated macrophage phagocytosing bacteria [] sem alveolar macrophage attacking E. coli [] tem macrophage-eosinophil [] micrograph macrophage surrounded by normal plasma cells [] micrograph macrophage & plasma cells [] micrograph erythroid island central macrophage [] micrograph foamy alveolar macrophage [] immunofluorescence tubulin in macrophage [] micrograph lymph node [] micrograph lymphoid follicle with germinal center H&E [] micrograph normal spleen [] micrograph macrophage & neutrophils in spleen [] thymus micrograph gallery [] macrophage attacking bacterium [] phagocytic embrace [] cartoon macrophage attacks []

Tables  Fc receptors  Immune Cytokines  Immunoglobulins

animations Џ Neutrophil Џ Platelet Response Џ Atopic Dermatitis Џ beautiful Flash 8 animation - inner life of the cell and Interpretation: Inner Life of the Cell Џ


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