No abstract
The thymus contains an extensive extracellular matrix. Although thymocytes express integrins capable of binding to matrix molecules, the functional significance of the matrix for T cell development is uncertain. We have shown that the matrix is associated with thymic fibroblasts which are required for the CD44 + CD25 + stage of double negative (CD4 -8 -) thymocyte development. The survival of cells at this stage is dependent on IL-7 and we propose that the role of fibroblasts is to present, via the matrix, IL-7 to developing T cells.
Four major inorganic cations --Na +, K--, Mg 2+ and Ca 2+ contribute mainly to the regulation of activity of muscle cells. The aim of the present comparative study was fo reveal the principal factors which determine the great variety of the cationic contents in different muscles of various animais. Functionally distinguished muscles of 70 species of marine, freshwater and terrestrial animals of 6 types of metazoans were investigated. The analysis of this muscle variability in regulation to the intracellular cati, onic contents has confirmed the qualitative heterogeneity of the muscle fibre populations investigated. The data obtained have permitted a subdivision of the latter into some definite groups, depending on the ionic composition of the extracellular fluids (environmental factor) as well as on the direction and the level of the functional specialization of muscles (inherent factor). In general a linear reciprocal relationship between [K+]i and [Na+]i in different skeletal muscles of various species was observed. In the saine organism an acceleration of a contractile response of the muscles is associated with an increase of a cellular selectivity of K § as compared to Na+; (SK/Na) -V c = A + B/SK/N,~. The character of this relation (the value of B) is species specific and reflects the level of development of a locomotory activity of the animais. At the same time the results obtained enable us to draw the conclusion that the trends in the cationic parameters in muscles do not coincide with the general course of the animal evolution. Itis demonstrated that the interrelation between functional (contractile) properties of skeletal muscles and cationic distribution patterns can be used as an 'ionic testing' method in medical-biological practice for diagnosing the physiological state of muscles. The results are discussed in terms of the physiological significance of inorganic cations involvement in the intracellular information transmission.
Despite the important role played by endogenous superantigen in shaping the T cell repertoire, little is known concerning the expression of the different Mtv loci in cells of the thymic microenvironment involved in repertoire selection. Here we have examined the expression of a panel of Mtv Ags by different MHC class II+ stromal cel types using reverse transcriptase-PCR and monitored the effects of these stromal cells on the development of cells expressing Mtv-reactive TCR V beta elements in closed thymic organ culture systems. Although Mtv-6 and Mtv-8/9 mRNAs are expressed in normal thymus lobe organ cultures, no Mtv expression was detected in MHC class II+ thymic epithelial cells. In contrast a striking pattern of differential expression was observed in dendritic cells of thymic origin that were devoid of Mtv-8/9 but expressed readily detectable levels of Mtv-6. This pattern of Mtv gene expression correlated well with TCR V beta repertoire development. TCRV beta 3+ T cells, normally deleted in response to Mtv-6, were virtually absent from the single positive thymocyte compartment in thymic organ cultures where dendritic cells are present but were present in reaggregate cultures where the only MHC class II-positive cells were thymic epithelial cells. On the other hand, V beta 11+ T-cells were not deleted in organ cultures, possibly reflecting the absence of Mtv-8/9 expression in dendritic cells. Our studies suggest that the influence Mtvs have on shaping the T cell repertoire not only depends on their expression within a particular strain but also on their tissue specific expression in relation to MHC class II, which is necessary for their presentation.
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