The regulation by iron of the synthesis of adhesins and cytoadherence levels in the protozoan Trichomonas vaginalis

Levels of adherence of Trichomonas vaginalis to epithelial cells was found to be modulated by iron. Cytoadherence values were greater than or equal to twofold higher for trichomonads grown in a complex cultivation medium supplemented with iron. This increase in adherence levels was specifically mediated by iron; parasites cultured in a low-iron medium in the presence of salts other than iron were unresponsive to changes in adherence levels. Expression of the higher adherence property, by parasites grown first in low-iron medium followed by supplementation with iron, was a function of time, and the extent of cytoadherence was proportional to the concentration of iron added to the medium. Lactoferrin, an important iron source for trichomonads at the site of infection, elevated adherence of the parasite to epithelial cells, demonstrating the likely in vivo modulation of adherence by iron. The alteration of levels of adherence caused by iron was determined to be a reflection of gene expression of previously characterized trichomonad adhesins. Parasites grown under iron-replete conditions had higher quantities of surface-exposed adhesins, and this was a result of increased synthesis of adhesins. Actinomycin D and alpha-amanitin prevented expression of adhesin molecules, which resulted in decreased cytoadherence, showing that adhesin synthesis was dependent on gene transcription. Data indicated that genes encoding the four trichomonad adhesins are coordinately regulated by iron

Specific erythrocyte binding is an additional nutrient acquisition system for Trichomonas vaginalis

Specific receptor-mediated binding by Trichomonas vaginalis of human erythrocytes was demonstrated. The ability of live parasites to internalize erythrocytes was also documented. In vitro growth assays during lipid-free and iron-limiting conditions that do not support the survival of T. vaginalis organisms showed that purified erythrocyte lipids and hemoglobin were each able to provide lipids and/or hemoglobin iron for trichomonal growth and multiplication. Parasites bound hemoglobin in a highly specific receptor-mediated fashion, and only the homologous unlabeled hemoglobin, but not lactoferrin and transferrin, competed with iodinated hemoglobin binding. Two antibody-crossreactive surface proteins of the parasites were identified as adhesins, and antibody to the individual adhesins inhibited T. vaginalis recognition and binding of erythrocytes. Finally, patient sera possessed antibody to the adhesins, showing the immunogenic nature and in vivo relevance of the trichomonad proteins during infection

Stress relaxation in the earth and seismic activity

Consideration of the models described in the preceding pages shows that a sound theoretical basis exists for a physical understanding of post-seismic ground deformations and several other phenomena associated with the asthenosphere relaxation. Since the asthenosphere seems to be involved in a direct way in the seismic mechanism, the knowledge of its rheological properties becomes an essential point to understand the seismic mechanism too. Once a reasonable knowledge of the asthenosphere behaviour is achieved, the models can tell us how the system lithosphere-asthenosphere will evolve after an earthquake or a similar perturbation of the stress field. It will be necessary to compute the stress pattern not only at the Earth surface, but also at the depth where the faults lay. By knowing how stress changes in space and time through the lithosphere, one might predict, for instance, the arrival of a stress wave on a seismogenetic structure: this wave might trigger an earthquake in this zone, if favourable conditions are found