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1.
The relapsing fever agent Borrelia hermsii avoids the host's immune response by the strategy of multiphasic antigenic variation. A given Borrelia cell can express one of a number of alleles for polymorphic outer-membrane proteins, known as Vmp proteins. The genes for the variant-specific Vmp proteins of serotypes 7 and 21 of B. hermsii strain HS1 were sequenced. The genes, which were designated vmp7 and vmp21, were obtained from populations of borreliae before and after a switch in serotypes from 7 to 21. The analysis showed that vmp7 and vmp21 are 77% identical in terms of their coding sequence. The deduced translation products of vmp7 and vmp21 are polypeptides of 369 (37.2 kD) and 364 amino acids (37.1 kD), respectively. Vmp7 and Vmp21 have sequence features of prokaryotic lipoproteins and are processed as such during expression in E. coli. The secondary structure predictions of the Vmp proteins reveals analogous structures to the VSG proteins of the African trypanosome.  相似文献
2.
Cryptococcus neoformans is an important pathogenic fungus that has been classified as a basidiomycete. Little is known of the molecular genetics of this fungal pathogen. To begin such studies, we devised a procedure for extraction of DNA from cryptococci; this method involved the use of the cell wall-active enzyme NovoZym 234. Using cloned rDNA of Saccharomyces cerevisiae as a probe, we identified homologous restriction fragments in a Southern blot of digested C. neoformans DNA. An 8.6-kilobase HindIII fragment that hybridized with the yeast rDNA probe was ligated with the vector pBR322 and cloned into Escherichia coli. When the fragment was used as a probe, it hybridized to the 18S and 25S rRNAs of C. neoformans in Northern (RNA) blots of native and denatured RNA. It bound at high stringency only weakly to the rRNAs of the ascomycete S. cerevisiae. The locations of the genes for 5/5.8S, 18S, and 25S subunits in the cloned fragment were identified with labeled rRNA of these different types.  相似文献
3.
Blood groups and HLA antigens in paracoccidioidomycosis   总被引:2,自引:0,他引:2  
The frequencies of blood groups, Rh and HLA antigens were studied in a series of patients with paracoccidioidomycosis as well as in control subjects. Statistical analysis of the results showed that only 2 antigens (HLA-A9 and HLA-B13) had a significantly increased frequency among patients with paracoccidioidomycosis compared with healthy controls. Among patients with paracoccidioidomycosis antigen HLA-A9 was significantly more prevalent in progressive pulmonary forms of the disease than in patients with extra pulmonary involvement. These observations suggest that HLA-A9 may influence susceptibility to the mycosis as well as its course.  相似文献
4.
Infection with the protozoan Leishmania donovani in humans is usually subclinical. Parasites probably persist for the life of the host and the low-level infection is controlled by the cellular immune response. To better understand the mechanisms related to the control of infection, we studied the evolution and architecture of the splenic cellular immune response in a murine model that is most representative of human subclinical infection. Following systemic inoculation with L. donovani, the parasites were primarily localized to the macrophage-rich splenic red pulp. There was an initial increase in the numbers of T cells and dendritic cells in the periarteriolar lymphoid sheath and marginal zone, but the red pulp (where parasitized macrophages were prominent) remained free of these cells until later in the course of infection. Thus, T cells did not colocalize with parasitized red pulp macrophages until later in the course of infection. Early in the course of infection, IL-10 production within the marginal zone and TGF-beta production by cells in the red pulp were prominent. These macrophage-inhibitory cytokines may contribute to the establishment of the infection and early parasite replication. By day 28 of infection, when the visceral parasite burden began to decline, the number of IL-10-producing spleen cells was back to the baseline level, but IFN-gamma production was higher and the number of IL-12-producing cells was increased dramatically. At this time T cells and dendritic cells had moved out of the lymphoid follicle and marginal zone into the red pulp where the parasites were located. These findings therefore suggest that control of infection is associated with IFN-gamma and IL-12 production and migration of T cells and dendritic cells to the site of chronic parasitism.  相似文献
5.
The present work focuses on the analysis of cell cycle progression of Paracoccidioides brasiliensis yeast cells under different environmental conditions. We optimized a flow cytometric technique for cell cycle profile analysis based on high resolution measurements of nuclear DNA. Exponentially growing cells in poor-defined or rich-complex nutritional environments showed an increased percentage of daughter cells in accordance with the fungus' multiple budding and high growth rate. During the stationary growth-phase cell cycle progression in rich-complex medium was characterized by an accumulation of cells with higher DNA content or pseudohyphae-like structures, whereas in poor-defined medium arrested cells mainly displayed two DNA contents. Furthermore, the fungicide benomyl induced an arrest of the cell cycle with accumulation of cells presenting high and varying DNA contents, consistent with this fungus' unique pattern of cellular division. Altogether, our findings seem to indicate that P. brasiliensis may possess alternative control mechanisms during cell growth to manage multiple budding and its multinucleate nature.  相似文献
6.
One of the differences observed between the two varieties of Cryptococcus neoformansis the greater difficulty to achieve an adequate therapeutical response in patients affected by C. neoformans var. gattii, an observation that has been validated in vitro only rarely. The aim of this work was to study the susceptibility patterns of 35 Colombian clinical isolates of C. neoformans, 20 of which belonged to the var. neoformans and 15 to the var. gattii. The minimal inhibitory concentration (MIC) was determined by broth microdilution, according to a modification of the methodology proposed by the National Committee for Clinical Laboratory Standards (NCCLS), using the breakpoints recently suggested by Nguyen et al. (Antimicrob Agents Chemother 1998; 42: 471-472). The antifungals tested were amphotericin B, fluconazole and itraconazole. Most of the isolates were susceptible to the three antimycotics tested regardless of the variety. Resistance to amphotericin B (MIC=2 microg/ml) was documented in two (10%) C. neoformans var. neoformans isolates; additionally, five (33%) C. neoformans var. gattii isolates felt in the category of fluconazole susceptible but dose dependent (MIC 16 microg/ml). In general, all C. neoformans var. gattii isolates proved susceptible only to the higher concentrations of the antifungals tested. For amphotericin B, seven (47%) isolates of this variety had MICs of 1 microg/ml, for fluconazole there were seven (47%) with MICs of 8 microg/ml and in the case of itraconazole, 10 isolates (66%) had MICs > 0.03 microg/ml. The data showed that although these isolates would be classified as susceptible, they actually require greater concentrations of the antifungals to be inhibited. This finding may well correlate both with the difficulty to attain therapeutic success in patients affected with C. neoformans var. gattii and with the need for more prolonged treatment courses in such cases.  相似文献
7.
The microniche of the dimorphic fungus Paracoccidiodes brasiliensisremains undefined in spite of the many attempts to isolate it from natural sources. Until recently, knowledge was also scanty concerning the presence of natural infections in animals; however, in the last decade, the fungus has been repeatedly isolated from the nine-banded armadillo, Dasypus novemcinctusin Brazil. A study aimed at determining the presence of infected armadillos in one of the paracoccidioidomycosis endemic areas of Colombia (Manizales, Department of Caldas) was undertaken. Based on the records of paracoccidioidomycosis patients available in the regional hospital, we selected a locality corresponding to a permanent resident, and found that it also had armadillo's burrows. Counting with the proper authorization, two animals were captured, sacrificed under prolonged anaesthesia and various internal organs cultured in mycological media. PCR with specific P. brasiliensis'primers was also done. The fungus was isolated from the mesenteric lymph node of one of the animals; fungal DNA amplification was positive in the same specimen as well as in the liver. The isolate from the Colombian armadillo indicates that these animals are regular hosts to P. brasiliensis in at least two endemic countries. Due to the restricted life pattern of these mammals they represent an important link with the natural habitat of the fungus. Consequently, a study of their movements and habits could prove rewarding in the search for this habitat.  相似文献
8.
Due to the high frequency of oral mucosal lesions observed in paracoccidioidomycosis patients, it was advocated that the infection was acquired by the traumatic implantation of the etiologic agent Paracoccidioides brasiliensis. Although at present this theory is considered invalid, it has not yet been excluded in experimental studies. In order to determine if intra-oral inoculation could explain the pathogenesis of paracoccidioidomycosis, 64 BALB/c mice were inoculated intra-orally with 850.000 viable P. brasiliensis conidia into the mandibular body. Animals were sacrificed at various time intervals up to 20 weeks and cultures were made from gingiva, lungs, spleen, and liver. Additionally, histopathological studies of the mandibular body were also performed. P. brasiliensis was isolated from all gingival tissues during the interval 24–72 h, indicating that the infection was active. During the 5–10 week period, the infection appeared to have been controlled at the inoculation site as cultures showed a significant reduction in colony forming units (CFU); however, at the 15–20 week period such control was lost and the fungus was recovered once more. Dissemination to other body sites was rare; thus, the lungs were involved in just one animal (2%), the liver in two (3%) and the spleen in seven (11%). The infection became established as proven by positive organ cultures, but the dissemination pattern did not correspond to the one observed in humans. Based on these findings, the intra-oral traumatic route does not appear to mimic the natural history of paracoccidioidomycosis. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献
9.
Water-in-oil (W/O) fermentation technology has the potential for overcoming the problems related with high broth viscosity in xanthan fermentations. By dispersing the aqueous broth in a continuous organic phase, the broth-thickening mechanisms are confined within the aqueous droplets without significantly increasing the overall viscosity. In this study, xanthan fermentations were made with perfluorocarbon (PFC) or vegetable oil as the organic phase. The results were compared with those obtained previously using n-hexadecane as the organic phase, to evaluate the effects of various properties. PFC provided easy phase separation at the end of fermentation but required higher power input for agitation, a direct result of its high density. The aqueous droplets formed were large (400–450 m), limiting the cell concentration employable due to the occurrence of oxygen starvation in the inner core. One main advantage of using vegetable oil was its low cost. In addition, vegetable oil provided much finer droplets (<120 m) and produced high xanthan concentrations (>100 g l–1). However, complete phase separation for product recovery was difficult to achieve. Fermentations in both organic phases were terminated by the occurrence of phase inversion to highly viscous O/W dispersions at aqueous-phase volume fractions of 0.53–0.56. The initial fraction was 0.3 but changed due to base addition for pH adjustment and nutrient addition for prolonged production.  相似文献
10.
The present work compares the effects of post-weaning crowding and those of food restriction on growth, body weight gain and the levels of several hormones, in male Sprague-Dawley rats. Crowding resulted in reduced food intake and diminished body weight gain. Rats daily receiving the same amount of food as that eaten by crowded rats (food-restricted group) showed similar body weight gain as crowded rats, but higher growth rate. Neither crowding nor food restriction altered the pituitary-adrenal axis. In contrast, both treatments decreased serum insulin, growth hormone (GH), somatomedin C (Sm-C) and thyroid-stimulating hormone (TSH) as compared to control rats. The reduction of GH and Sm-C levels was similar in crowded and food-restricted rats but that of TSH was higher in food-restricted, rather than in crowded rats. The present data indicate that the effects of crowding could only be partially explained by the concomittant reduction of food intake and that the serum levels of the hormones studied could not explain the differences between the crowded and food-restricted rats with regard to growth.  相似文献
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