Prostaglandin E2 inhibits the activation of cloned T cell hybridomas

To minimize complicating interactions inherent in heterogeneous cell populations, we used a panel of cloned murine autoreactive (E8.A1) and antigen-specific (HEL.C10, HEL.B14) T cell hybridomas to examine the effect of prostaglandin E2 (PGE2) on T cell activation. These T cells secrete interleukin 2 (IL 2) when co-cultured with a cloned population of I region-matched stimulator cells (TA3), or with mitogenic signals in the absence of TA3 stimulator cells. Physiologic concentrations of PGE2 inhibited the induction of IL 2 secretion by the T cell hybridomas tested, when they were activated either by TA3 cells or by mitogenic signals. IL 2 production was inhibited in a dose-dependent manner by concentrations of PGE2 between 10(-7) and 10(-11) M, with 50% inhibition occurring at 10(-10) M. Pretreatment of the T hybridoma cells with 10(-7) M PGE2 for 1 hr before culture also resulted in marked inhibition of IL 2 secretion. Similar pretreatment of the TA3 cells did not affect their ability to activate the T cell hybridomas. PGE2 at 10(-8) M induced a 30-fold increase in cAMP levels within 25 min of addition to culture of the E8.A1 T cell hybridoma, but caused no significant elevation of cAMP levels in TA3 cells. The direct addition of dibutyryl cAMP (dcAMP) to cultures of E8.A1 cells resulted in marked inhibition of IL 2 secretion when stimulated by TA3 or by mitogenic signals, with an average of 80% inhibition occurring at 10(-4) M dcAMP. PGE2 and dcAMP also inhibited the growth of E8.A1 cells. Initially, cell growth was virtually halted, but began to recover between 24 and 48 hr after the addition of either PGE2 or dcAMP. Neither PGE2 nor dcAMP inhibited the division of TA3 cells. High affinity binding sites for PGE2 were detected in the E8.A1 T cell hybridomas with an apparent Kd of 7.6 X 10(-10) M, which is consistent with the functional data. No specific binding was detected in the TA3 stimulator cells. These findings suggest that the immunosuppressive effects of PGE2 are localized to the T cell, are receptor regulated, and may be mediated by the associated increase of cAMP levels in the T cell hybridomas.     

Evidence Inconsistent with the Blaauw Model of Phototropism

The Blaauw model of phototropism equates the inhibition of growthat the illuminated side of a unilaterally illuminated organwith the blue light inhibition of overall organ extension evidentwhen some shoots are exposed to uniform blue light However,a study of the growth responses of Avena coleoptiles exposedto omnilateral, equal bilateral, unequal bilateral and unilateralblue light has revealed some light induced growth rate changeswhich cannot be explained by the Blaauw model. The growth responsesof cells at the illuminated and shaded sides of phototropicallystimulated coleoptiles seem to depend on the existence of alight gradient across the whole organ rather than the absolutelevels of light at either side. Key words: Phototropism, Avena coleoptile, Blaauw hypothesis, Blue light, Growth inhibition     

Escherichia coli CAN lacks a tRNA-processing nuclease.

Escherichia coli strain CAN is unable to support the growth of bacteriophage T4 strains requiring the suppressor function of T4 tRNASer. Biochemical analysis of the mutant strain revealed that it is deficient in a RNase which acts on the artificial tRNA precursor tRNA-C-U.     

The Effect of Decreasing the External Salinity on the Primary Processes of Photosynthesis in Dunaliella tertiolecta

The euryhaline unicellular green alga Dunaliella tertiolectalost intracellular glycerol when subjected to a decrease inexternal salinity. After the salinity was decreased, photosynthesiswas inhibited for at least the first 100 min, but dark oxygenuptake was transiently stimulated. The extent of the 519 nmfield-indicating absorption change induced by photosystem Ialone was inhibited by decreasing the salinity, but other photosyntheticparameters were largely unaffected. A comparison of these resultswith hypertonic stress indicated that although both stressesinhibit the overall process of photosynthesis, they do so bydifferent mechanisms. Resuspending the algal cells in distilledwater resulted in an inhibition of all the photosynthetic parametersmeasured. Key words: Dunaliella, Photosynthesis, Hypotonicity     

Manifestations of angina morbidity as a reflection of the self-regulation of the epidemic process in streptococcal infection

The data on the application of the principles of the self regulation of the epidemic process for understanding the annual dynamics of angina morbidity in organized groups of adults are presented. In this case the reservation of group A streptococci occurs in chronic (resident) carriers, whose proportion was found to be 15.8 +/- 2.6%. The epidemic manifestations of morbidity are regulated mainly by the concentration of newly arrived members in the groups, i. e. by the size of the stratum providing the optimum conditions for the parasitization of the streptococcal population. The annual morbidity levels depend essentially not only on the heterogeneity of the group members with respect to their susceptibility to streptococcal infection, but also on the conditions of their accommodation, affecting the transmission of droplet infection. The role of individual risk factors in the variation of the quantitative characteristics of the angina morbidity manifestations under study is calculated.     

Genetic diversity of durum wheat as determined by AFLP in fluorescence

The DNA of fifteen Italian cultivars of durum wheat (Triticum turgidum L. ssp. durum) were analyzed by in fluorescence amplified fragment length polymorphism (fAFLP) in order to obtain the characteristic fingerprintings of genotypes and assess their genetic relatedness. Among 64 combinations of fluorescence labelled primers, three different combinations were chosen as producing a total of 6630 AFLP fragments, 2277 (34.3 %) of them being polymorphic. By using this fAFLP methodology a DNA fingerprinting of each durum wheat cultivar was generated for genotype identification. Analysis of the genetic relationships show the low variability among durum wheat cultivars.     

The physical mechanism of calcium pump regulation in the heart.

The Ca-ATPase in the cardiac sarcoplasmic reticulum membrane is regulated by an amphipathic transmembrane protein, phospholamban. We have used time-resolved phosphorescence anisotropy to detect the microsecond rotational dynamics, and thereby the self-association, of the Ca-ATPase as a function of phospholamban phosphorylation and physiologically relevant calcium levels. The phosphorylation of phospholamban increases the rotational mobility of the Ca-ATPase in the sarcoplasmic reticulum bilayer, due to a decrease in large-scale protein association, with a [Ca2+] dependence parallel to that of enzyme activation. These results support a model in which phospholamban phosphorylation or calcium free the enzyme from a kinetically unfavorable associated state.     

Specific silver staining of experimentally undercondensed chromosome regions

Treatment of human and mouse cell cultures with DNA binding AT-specific compounds and with some base analogues induced distinct undercondensations in several heterochromatic chromosome regions. All those heterochromatic regions undercondensed by AT-specific DNA ligands (distamycin A, DAPI, Hoechst 33258) could be heavily labeled with the silver(Ag)-staining technique; but the heterochromatic regions undercondensed with the cytidine analogue 5-azacytidine were Ag-negative. In metaphase chromosomes from BrdU-treated human cell cultures, the bifilarly substituted chromatids, which show a slight undercondensation, were also Ag-negative. Cytochemical analyses of the Ag-stained undercondensed heterochromatic regions showed that the Ag-stainable material consisted of nonhistone proteins. The mechanism of Ag staining in the undercondensed heterochromatic regions was compared with Ag staining of the nucleolus organizer regions.