Information AboutCytokine |
| CATEGORIES ABOUT CYTOKINE | |
| cytokines | |
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EFFECTS Each Cytokine binds to a specific cell-surface receptor. Subsequent intracellular signalling cascades then alter cell functions. This may include the upregulation and/or downregulation of several Genes and their Transcription Factors , that result in production of other cytokines, or increase in the number of surface receptors for other molecules, or suppress their own effect by feedback inhibition. Therefore, cytokines are characterised by considerable redundancy, in that many cytokines can share similar functions. In a similar manner, cytokines are also ''' Pleiotropic ''' (acting on many different cell types). Of course, this would be an anticipated corollary if one considers the simple fact that a given cell type may express receptors for more than one cytokine, or that many different tissues can express receptors for the same cytokine. Generalisation of functions is not possible with cytokines; nonetheless, their actions may be comfortably grouped as:
Cytokines binding to antibodies paradoxically have a stronger immune effect than the cytokine alone. This may lead to lower therapeutic doses and perhaps fewer side effects. NOMENCLATURE Cytokines have been variously named as lymphokines, Interleukins and Chemokines , based on their presumed function, and their cell of secretion or target of action. Because cytokines are characterised by considerable redundancy and pleotropism, such a distinction, with exceptions, is obsolete. The term interleukin was initially used by researchers for those cytokines whose presumed targets are principally Leukocytes . The term '''chemokine''' referred to a specific class of cytokines that mediated chemoattraction (chemotaxis) between cells. The latter term alone has been retained (see below); interleukins are now used largely for designation of newer cytokine molecules discovered every day, and have little significance attached to their presumed function. Of note, IL-8 (interleukin-8) is the only chemokine originally named an interleukin. CLASSIFICATION Cytokines have now been classified into four different types based on structural homology, which has been partly able to separate cytokines that do not demonstrate a considerable degree of redundancy.
A more clinically and experimentally useful classification divides immunological cytokines into those that promote the proliferation and functioning of helper T-cells type 1 (example, IL-1, INF-γ etc.) and helper T-cells type 2 (IL-4, IL-10, IL-13, TGF-β etc.), respectively. It is remarkable that the cytokines that belong to one of these sub-sets tend to inhibit the effects of their counterparts - a tendency under intensive study for their possible role in the pathogenesis of autoimmune disorders. CYTOKINE RECEPTORS In recent years, the cytokine receptors have come to demand the attention of more investigators than cytokines themselves, partly because of their remarkable characteristics, and partly because a deficiency of cytokine receptors have now been directly linked to certain debilitating immunodeficiency states. In this regard, and also because the redundancy and pleomorphism of cytokines are in fact a consequence of their homologous receptors, many authorities are now of the opinion that a classification of cytokine receptors would be more clinically and experimentally useful. A classification of cytokine receptors based on their three-dimensional structure has therefore been attempted. (It must be noted that such a classification, though seemingly cumbersome, provides with several unique perspectives for attractive pharmacotherapeutic targets.)
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