Statement issued by the natural science society of China and the Chinese association of scientific workers

Ohne Zusammenfassung     

Estimation and Prediction for Stochastic Blockmodels for Graphs with Latent Block Structure

a posteriori blockmodeling for graphs is proposed. The model assumes that the vertices of the graph are partitioned into two unknown blocks and that the probability of an edge between two vertices depends only on the blocks to which they belong. Statistical procedures are derived for estimating the probabilities of edges and for predicting the block structure from observations of the edge pattern only. ML estimators can be computed using the EM algorithm, but this strategy is practical only for small graphs. A Bayesian estimator, based on the Gibbs sampling, is proposed. This estimator is practical also for large graphs. When ML estimators are used, the block structure can be predicted based on predictive likelihood. When Gibbs sampling is used, the block structure can be predicted from posterior predictive probabilities. A side result is that when the number of vertices tends to infinity while the probabilities remain constant, the block structure can be recovered correctly with probability tending to 1.     

Activated human eosinophils generate SRS-A leukotrienes following IgG-dependent stimulation

Eosinophils, a class of granular leukocytes, are prominent in many inflammatory processes, particularly in asthma, certain allergic diseases and during infections with helminthic parasites. Following incubation with the Ca ionophore A23187 (refs 1-4) (a non-physiological agent which circumvents membrane calcium-gating mechanisms), eosinophils generate large amounts of sulphidopeptide leukotrienes, potent inducers of smooth muscle constriction and mucus production. These are now known to represent the activity previously termed 'slow-reacting substance of anaphylaxis' (SRS-A) but attempts to identify a physiological stimulus for SRS-A production by eosinophils have so far been unsuccessful. The cells contain recognized receptors for IgG (Fc) and it is known that they adhere to, and can be activated by, contact with the surface of large organisms such as helminthic larvae. We show here that eosinophils, particularly when activated, produce sulphidopeptide leukotrienes after contact with large particles coated with IgG.     

Immunological activity of covalently linked T-cell epitopes.

Immune responses to proteins necessarily involve the recognition by T lymphocytes of a peptide or peptides derived from a protein complexed with a major histocompatibility antigen. The T-cell response of BALB/c mice to the bacteriophage lambda cI repressor protein (residues 1-102) is directed predominantly towards the epitope contained within a single peptide encompassing residues 12-26. Similar phenomena of immunodominance of a particular peptide have also been observed in other protein systems. The mechanisms that have been suggested to account for the focusing of the T-cell response are partial deletion in the T-cell repertoire, biased antigen processing, and competition for binding to the presenting molecule, the major histocompatibility complex encoded class II transplantation antigen. In a model system with a polypeptide containing two synthetically linked immunologically active epitopes, we now demonstrate the existence of a hierarchy between these epitopes, so that the immune response elicited is directed mainly towards the more immunogenic epitope, whereas the less immunogenic epitope elicits little or no T-cell reactivity. In addition, the same hierarchy of dominance is also apparent when the polypeptide is used to induce tolerance in the periphery in adult mice. The chimaeric peptide can induce tolerance only towards the more immunogenic epitope. These experiments indicate that the rules governing antigen processing and presentation that result in T-cell activation are apparently the same as the rules that govern the processes resulting in the induction of tolerance.     

Pyruvate kinase inhibited by L-cysteine as a marker of tumorigenic human urothelial cell lines

Summary It was found that a decrease in electrophoretic mobility of pyruvate kinase (PK) isoenzyme, and an increase of the sensitivity of this enzyme to L-cysteine, were markers of immortalization and tumorigenic properties, respectively, in human urothelial cell lines characterized by different grades of transformation (TGr) in vitro.     

Interaction of extrinsic fluorescent probes with E. coli glutamine synthetase.

Binding of 2-p-toluidinylnaphthalene-6-sulfonate (TNS) to adenylylated (E--11) glutamine synthetase is cooperative and time-dependent, with 3 dye sites per subunit. In fluorescence polarization experiments TNS and pyrene butyrate give normalized Perrin plots that indicate a symmetrical arrangement of dye excited state dipoles, relative to the rotational axis of the oblate ellipsoid of the dodecameric native enzyme.