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101.
102.
Tom A. B. Snijders Maarten Dormaar Wijbrandt H. van Schuur Chantal Dijkman-Caes Ger Driessen 《Journal of Classification》1990,7(1):5-31
Parameters are derived of distributions of three coefficients of similarity between pairs (dyads) of operational taxonomic units for multivariate binary data (presence/absence of attributes) under statistical independence. These are applied to test independence for dyadic data. Association among attributes within operational taxonomic units is allowed. It is also permissible for the two units in the dyad to be drawn from different populations having different presence probabilities of attributes. The variance of the distribution of the similarity coefficients under statistical independence is shown to be relatively large in many empirical situations. This result implies that the practical interpretation of these coefficients requires much care. An application using the Jaccard index is given for the assessment of consensus between psychotherapists and their clients.
La distribution des coefficients de similarité pour les données binaires et les attributs associés
Résumé Les paramètres de la distribution de trois coefficients de similarité entre paires d'éléments taxinomiques opérationels de données multivariables binaires (présence/absence) ont été dérivés dans l'hypothèse d'indépendance statistique. Ces paramètres sont utilisés dans un test d'indépendance pour les données dyadiques. L'existence est autorisée, dans la population d'éléments, d'une association entre plusieurs attributs. Il est également permis que les deux éléments de la dyade soient tirés de deux populations différentes, ayant différentes probabilit és quant à la présence des attributs. Dans beaucoup de situations empiriques, la variance des coefficients de similarité peut être relativement élevée dans le cas d'indépendance statistique. Par conséquence, ces coefficients doivent être interprétés avec précaution. Un exemple est donné pour le coefficient de Jaccard, qui a été employé dans une recherche sur la concordance entre des psychothérapeutes et leurs clients.相似文献
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Enhancement of LFA-1-mediated cell adhesion by triggering through CD2 or CD3 on T lymphocytes 总被引:61,自引:0,他引:61
Y van Kooyk P van de Wiel-van Kemenade P Weder T W Kuijpers C G Figdor 《Nature》1989,342(6251):811-813
The lymphocyte function-associated molecule LFA-1 (CD11a/CD18) plays a key part in lymphocyte adhesion. Lymphocytes do not adhere spontaneously; activation of protein kinase C (PKC) by phorbol esters, however, gives rise to strong LFA-1-dependent adhesion, indicating that activation of LFA-1 is required to induce cell adhesion. We have now investigated whether the functionally important CD2 and CD3 surface structures on T lymphocytes are involved in the activation of LFA-1. The stimulation of these molecules, which causes activation of PKC, strongly promoted LFA-1-dependent adhesion. Furthermore, we demonstrate by using cells from an LFA-1-deficient patient that this enhanced lymphocyte adhesion is caused by activation of the LFA-1 molecule and not by activation of its ligands. LFA-1 was persistently activated by triggering through CD2 but only transiently by triggering through CD3. We postulate that CD2 and CD3 can differentially regulate the affinity of LFA-1 for its ligands by modulating its molecular conformation through PKC-dependent mechanisms. 相似文献
105.
Isolation and characterization of a cDNA clone encoding the murine homologue of the human 20K T3/T-cell receptor glycoprotein 总被引:1,自引:0,他引:1
The antigen receptor on the surface of human T lymphocytes, which consists of a heterodimer of relative molecular mass (Mr) 90,000 (90K) (alpha- and beta-chains), is associated with the T3 antigen (gamma = 25K, delta = 20K and epsilon = 20K). A working model for the mode of action of the T3/T-cell receptor complex is that the clonotypic alpha- and beta-chains are involved in the recognition and binding of antigen in the context of polymorphic major histocompatibility complex (MHC) gene products on the surface of target cells. Antigen binding by the clonotypic receptor probably results in conformational changes in this structure which are recognized by and subsequently trigger the associated T3 complex to transmit signals into the cell, resulting in a proliferative response. The similarity in structure between murine and human clonotypic antigen receptors suggests that such a mechanism of recognition and activation also exists in mouse T lymphocytes, but so far there has been no evidence for the existence of a murine T3 complex. Here we demonstrate the existence of a T3 delta-chain mRNA in murine T lymphocytes. Our sequence data strongly suggest that this mouse mRNA codes for a complete T3 delta polypeptide chain and reveal some interesting properties of the protein. 相似文献
106.
N de Wind M Dekker N Claij L Jansen Y van Klink M Radman G Riggins M van der Valk K van't Wout H te Riele 《Nature genetics》1999,23(3):359-362
Cancer predisposition in hereditary non-polyposis colon cancer (HNPCC) is caused by defects in DNA mismatch repair (MMR). Mismatch recognition is attributed to two heterodimeric protein complexes: MutSalpha (refs 2, 3, 4, 5), a dimer of MutS homologues MSH2 and MSH6; and MutSbeta (refs 2,7), a dimer of MSH2 and MSH3. These complexes have specific and redundant mismatch recognition capacity. Whereas MSH2 deficiency ablates the activity of both dimers, causing strong cancer predisposition in mice and men, loss of MSH3 or MSH6 (also known as GTBP) function causes a partial MMR defect. This may explain the rarity of MSH6 and absence of MSH3 germline mutations in HNPCC families. To test this, we have inactivated the mouse genes Msh3 (formerly Rep3 ) and Msh6 (formerly Gtmbp). Msh6-deficient mice were prone to cancer; most animals developed lymphomas or epithelial tumours originating from the skin and uterus but only rarely from the intestine. Msh3 deficiency did not cause cancer predisposition, but in an Msh6 -deficient background, loss of Msh3 accelerated intestinal tumorigenesis. Lymphomagenesis was not affected. Furthermore, mismatch-directed anti-recombination and sensitivity to methylating agents required Msh2 and Msh6, but not Msh3. Thus, loss of MMR functions specific to Msh2/Msh6 is sufficient for lymphoma development in mice, whereas predisposition to intestinal cancer requires loss of function of both Msh2/Msh6 and Msh2/Msh3. 相似文献
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P H van der Bosch de Aguilar 《Experientia》1976,32(2):228-229
The activity of Artemia protocerebral median neurosecretory cells is stimulated when animals are grown in media whose tonicity is lower than that of sea weater. The substance liberated by these cells could regulate the tonicity of the internal medium. 相似文献