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Related post: 1992 Annual Report Table of Contents ZOl-AI Project Number Summary 00485-06 00613-02 00486-06 00581-03 T Cell Activation—Schwartz T Cell Subsets-Schwartz T Cell Differentiation— Fowlkes T Cell Memory and Tolerance—Matzinger Page 6-1 6-6 6-7 6-8 6-9 PHS-NIH Summary Statement Office of the Chief Laboratory of Cellular and Molecular Immunology October 1, 1991 through September 30, 1992 Introduction The Laboratory of Cellular and Molecular Immunology was created in November, 1986. Its major task is to perform research on thymus-derived (T) lymphocytes. Its objective is to understand how these critical cells of the immune system differentiate and function. The approach is to define problems in whole animal systems, set up in vitro analogs in tissue culture, and determine the molecular basis for the phenomena. The laboratory employs techniques from the disciplines of cellular immunology, molecular biology, and protein biochemistry. During its sixth year, the laboratory has pursued four major areas of research: 1) the molecular nature of costimulation, 2) the meaning of a half maximal response for interleukin 2 production, 3) T cell receptor aP lineage commitment and the affinity model for repertoire selection in thymic development and 4) fetal thymic stem cells, T cell life span, T cell recirculation and tolerance to tissue specific antigens. T Cell Activation Studies of T cell activation of normal murine T cell clones of the T^l type have shown that two signals are required to stimulate the cells to make interleukin-2 (lL-2) and divide. One signal is given through the antigen-specific receptor that is uniquely expressed on each clone. The other signal is called costimulation and is delivered through a different receptor. Our major objective during the past year was to characterize the costimulatory signal. Other laboratories had identified the B7/BB1 molecule as the inducible ligand on the APC and CD28 and CTLA-4 on the T cell as potential receptors for costimulation in the production of interleukin-2 (IL-2). We explored the role of these molecules in a new assay for costimulation, the induction of competence to respond to interleukin-4 (IL-4). Murine T^l clones do not respond directly to IL-4. They first must be activated by stimulating them with antigens and APC. After 24 hr. the activated T cells then proliferate in response to IL-4. We demonstrated that costimulation is required during the induction phase in order to make the clones competent to proliferate in response to IL-4. Although supplying costimulation also led to the production of IL-2, stimulation with this lymphokine was not the only signal required to gain competence, because addition of IL-2 to a T cell receptor occupancy signal only allowed the cells to become partially competent to respond to IL-4. We concluded from these experiments that the costimulatory signal contributes directly to the attainment of full competence to respond to IL-4. To explore the molecules involved in this costimulation, we used a recombinant fusion protein between CTLA4 and a human Ig immunoglobulin constant region. This molecule reacts with B7/BB 1 expressed on activated Buy Intagra antigen-presenting cells. We showed that CTLA4Ig could inhibit proliferation and IL-2 production of both ThI and ThO murine clones but not IL-4 production by the latter. In addition it inhibited the ability of 6-1 ThI clones to gain competence to respond to IL-4. We concluded from these experiments that B7/BB1 is the critical ligand involved in costimulation for both IL-2 production and the gaining of competence to respond to IL-4. (S. Umlauf, K. Brorson, S. Kitagawa, L. Chiodetti, and R. H. Schwartz, LCMI, MAID; P. Linsley, Bristol-Meyers Squibb) T Cell Subsets When a population of T cells divides in response to an antigenic stimulus a range of concentrations of the antigen is required to go from no cells dividing to all the cells dividing. At the concentration required to achieve one-half of the maximal response, it has been demonstrated that one-half of the cells are dividing. The production of lymphokines by T cells shows a Intagra 100 similar dose-response curve to antigen. However, the interpretation of the half- maximal response is not necessarily the same. Either all the cells are producing only one-half of their maximal potential, or one half of the cells are producing at their full potential while the other half are producing nothing. To decide between these two alternatives we examined the production of interleukin 2 by single T cell clones at different concentrations of antigen. The response appeared to be quantal (all or none) but two different levels of response were observed, one approximately 3-4 times the other. Furthermore, the dose response curve was biphasic with a decrease in the number of cells in each group at higher (>30nM) antigen concentrations. Our interpretation of these results is that induction of transcription of the IL-2 gene is what is quantal. Thus, the group of cells giving the low level of IL-2 production had only one chromosome being transcribed, whereas the group giving the higher level of IL-2 production was transcribing both chromosomes. The fact that all the cells were not found in the high positive group at large antigen concentrations possibly reflects a negative feedback regulation on IL-2 transaiption. Experiments are currently in progress to test these two hypotheses. (B. Beverly, A. Bendelac, D. Cassell, and R. H. Schwartz, LCMI, NIAE); D. Ailing, NCI, NIAID) T Cell Differentiation During T cell development, thymocytes that are able to recognize self MHC are signalled to mature (positive selection), whereas those capable of self reactivity are selected to die (negative selection). Our studies deal with the paradox of how signaling resulting from a specific TCR-MHC interaction can determine the positive or negative selection events. Several investigations involving TCR transgneic mice revealed that distinct thymic antigen
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