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Microglia are a type of glial cell located throughout the brain and spinal cord of the central nervous system (CNS). [1] Microglia account for about 10–15% of cells found within the brain. [2] As the resident macrophage cells, they act as the first and main form of active immune defense in the CNS. [3]
These histiocytes are part of the immune system by way of two distinct functions: phagocytosis and antigen presentation. Phagocytosis is the main process of macrophages and antigen presentation the main property of dendritic cells (so called because of their star-like cytoplasmic processes).
The blood–brain barrier is formed by the brain capillary endothelium and excludes from the brain 100% of large-molecule neurotherapeutics and more than 98% of all small-molecule drugs. [28] Overcoming the difficulty of delivering therapeutic agents to specific regions of the brain presents a major challenge to treatment of most brain disorders.
These T cells bind to the MHC II-antigen molecule and cause activation of the B cell. This is a type of safeguard to the system, similar to a two-factor authentication method. First, the B cells must encounter a foreign antigen and are then required to be activated by T helper cells before they differentiate into specific cells. [8]
CD34 is expressed in hematopoietic progenitor cells and endothelial cells of blood vessels. Thus, it has been used as a marker for capillaries and blood vessels. One of the most densely vascular organs is the kidney, wherein networks of capillaries are intertwined with renal tubules.
There are four types of granulocytes (full name polymorphonuclear granulocytes): [3] Basophils; Eosinophils; Neutrophils; Mast cells; Except for the mast cells, their names are derived from their staining characteristics; for example, the most abundant granulocyte is the neutrophil granulocyte, which has neutrally staining cytoplasmic granules.
In contrast, the B cell antigen-specific receptor is an antibody molecule on the B cell surface and recognizes native (unprocessed) antigen without any need for antigen processing. Such antigens may be large molecules found on the surfaces of pathogens, but can also be small haptens (such as penicillin) attached to carrier molecule. [60]
CD1 (cluster of differentiation 1) is a family of glycoproteins expressed on the surface of various human antigen-presenting cells.CD1 glycoproteins are structurally related to the class I MHC molecules, however, in contrast to MHC class 1 proteins, they present lipids, glycolipids and small molecules antigens, from both endogenous and pathogenic proteins, to T cells and activate an immune ...