Target-cells

The term hormone is used to denote a chemical substance, released from a cell into the extracellular fluid in low quantities, which acts on a target cell to produce a response. Hormones are classified on the basis of chemical stmcture most hormones are polypeptides, steroids (qv), or derived from single amino acids (qv) (Table 1). 

Receptor Regulation and Defects. Specific recognition and the initiation of response are the accepted attributes of the dmg—receptor interaction. However, target cells can alter on both short- and long-term time scales their sensitivity to dmgs. Such regulation, achieved by altering the... 

The term endocrine disrupter (ED) has tended to be used for those chemicals which act specifically at the level of the hormone receptor present in the target cells of various organs. Such chemicals may either mimic the action of the natural hormone (agonistic activity) or are sufficiently similar in molecular shape to the naturally produced hormone to interfere with the interaction between the hormone and receptor, thus blocking or impeding the activation of the receptor (antagonsitic activity). Such effects may occur at very low concentrations (as with the endogenous hormone), compared with the concentrations normally required to elicit the more traditional toxic effects attributed to chemicals. Recently,... 

Oestrogen action is mediated through specific receptors localised within the nucleus of target cells (see Carson-Jurnica et and Tsai and O Malley " for... 

Insulin is composed of two peptide chains covalently linked by disulfide bonds (Figures 5.17 and 6.35). This monomer of insulin is the active form that binds to receptors in target cells. However, in solution, insulin spontaneously forms dimers, which themselves aggregate to form hexamers. The surface of the insulin molecule that self-associates to form hexamers is also the surface that binds to insulin receptors in target cells. Thus, hexamers of insulin are inactive. 

The biological actions of adrenaline and noradrenaline are mediated via nine different G-protein-coupled receptors, which are located in the plasma membrane of neuronal and nonneuronal target cells. These recqrtors are divided into two different groups, a-adrenergic receptors and P-adrenergic recqrtors (see P-adrenergic system). 

Allergy. Figure 2 Histamine H-1 receptor antagonists inhibit response of target cells to histamine and relieve hay fever-like symptoms. 

Allergy. Figure 3 Leukotriene LT receptor antagonists inhibit the response of target cells to leukotrienes and relieve symptoms of allergic asthma bronchiale. 

A mechanism of cell-mediated immunity whereby an effector cell of the immune system actively lyses a target cell that has been bound by specific antibodies. The typical ADCC involves activation of natural killer (NR) cells and is dependent on the recognition of... 

Proteins embedded in the shell of lipoproteins. They serve as scaffold for assembly of the lipoprotein particle in the endoplasmic reticulum. In addition, they control metabolism of lipoproteins in the circulation by interaction with enzymes such as lipases. Finally, apolipoproteins determine cellular uptake of the particles by interaction with specific lipoprotein receptors expressed on the surface of target cells. 

Two distinct populations of neurons in the arcuate nucleus have been identified as the most relevant target cells of leptin (Fig. 1, [2, 4]). Leptin inhibits expression... 

The anthrax toxin is a tripartite toxin and consists ofthe binding component protective antigen (PA), the lethal factor (LF), which is a metalloprotease, and the edema factor (EF), which is a calmodulin-dependent adenylyl-cyclase. Both enzyme components are translocated via PA into target cells. PA is activated by furin-induced cleavage and forms heptamers, which are similar to the binding components of C2 toxin and iota toxin. In the low pH compartment of endosomes, the heptamers form pores to allow translocation of LF and EF. LF cleaves six of the seven MEKs (MAPK-kinases) thereby inhibiting these enzymes. The functional consequence is the blockade of the MAPK pathways that control cell proliferation, differentiation, inflammation, stress response, and survival. Whether this is the reason for the LT-induced cell death of macrophages is not clear [1]. 

An important safety issue of viral vectors is whether or not the recombinant viruses are able to replicate in the infected cells. Replication of viral vectors is unwanted in most gene-therapy approaches. Therefore, replication-defective vectors have been designed, which are able to perform only one initial infectious cycle within the target cell. In addition, replication-competent vectors have been designed, which are able to productively infect the target cell and to spread in the target tissue. 

The main transport form of lipids in the cir culation. They are spherical macromolecules of 10-1200 nm diameter-composed of a core of neutral lipids (mostly cholesterol ester and triglycerides) surrounded by an amphipathic shell of polar phospholipids and cholesterol. Embedded in the shell of lipoproteins are apolipoproteins that are essential for assembly of theparticles in tissues that secrete lipoproteins, and for their recognition by target cells. 

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