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31.
32.
Studies were performed to determine the development of cell-mediated cytotoxic response at tumor site in C57BL/6 mice bearing progressively growing FBL-3 ascites leukemia. The effectors isolated from tumor ascites are found to be highly cytotoxic for leukemic target cells. The levels of cytotoxicity obtained with effectors isolated from tumor site are generally higher than those obtained with immune mice. This cytotoxicity is both specific and nonspecific. The specific cytotoxicity against tumor-associated antigen is mainly mediated by T cells and the nonspecific cytotoxicity against unrelated tumor cells is mediated largely by macrophages. The T-cell-enriched preparation did not give significant natural killer activity. When testing the ability of these effectors to produce in vivo immunity against the challenge of FBL-3, it was found that only T cells could confer the transplantation-type immunity, but the immunity was transient. The macrophage-enriched preparation isolated from tumor ascites failed to give in vivo protection. These findings indicate that in FBL-3 system, mice with progressively growing tumors are able to develop immune response against tumor cells. However, this immunity is probably interfered with by a suppressor factor(s) or suppressor cells which restrict their activity to eliminate the tumor cells effectively. 相似文献
33.
J Cabrita J Rodrigues F Bragan?a C Morgado I Pires A P Gon?alves 《The Journal of applied bacteriology》1992,73(4):279-285
The incidence of Campylobacter jejuni and Campylobacter coli in wild and producing animals has been studied to evaluate their importance as potential reservoirs of campylobacter infection. These organisms were isolated from: 59 chicken (60.2%), 65 swine (59.1%), 31 black rats (57.4%), 61 sparrows (45.5%), 21 ducks (40.5%), 32 cows (19.5%) and 27 sheep (15.3%). Biotypes, plasmid and resistance profiles were studied in order to characterize the isolates. Biotypes I and II of C. jejuni were predominant in all reservoirs except swine, where C. coli I was more frequent. Plasmid prevalence was higher in strains isolated from swine (53.8%) and rats (45.5%). The size of the plasmids ranged from 1.3 to 82 MDa. A 2.3 MDa plasmid was the most frequent, detected in all the reservoirs except ducks. Antimicrobial susceptibility testing revealed that 5.5% of the strains were resistant to ampicillin, 5.5% to tetracycline, 12.6% to erythromycin and 23.5% to streptomycin. Resistance to erythromycin (26.2%) and to streptomycin (58.4%) was particularly high in isolates from swine. Tetracycline resistance was encoded by a 33 or a 41 MDa plasmid and transferred by conjugation. 相似文献
34.
Carol A. Bonner Astride M. Rodrigues Jacqueline A. Miller Roy A. Jensen 《Physiologia plantarum》1992,84(3):319-328
The growth of Nicotiana silvestris in suspension culture is inhibited by all of the common protein amino acids at the millimolar level, except for L-glutamine. A defined experimental system for growth/inhibition studies has been established, and growth studies were carried out with cells that had been maintained in the exponential growth phase for at least 10 generations (EE cells). The following results were obtained after particularly detailed studies with aromatic amino acids. The onset of inhibition was preceded by a duration of normal growth rate which varied within a range of 12 to 48 h. The degree of inhibition was directly proportional to amino acid concentration and inversely related to the initial cell density of the inoculum. A slowed, but still exponential rate of growth persisted during an early phase of inhibition. Under sufficiently severe conditions, this was followed by progressive diminution of growth rate and eventual lysis. The most drastic inhibitory effects caused by aromatic amino acids were in the order: phenylalanine, tryptophan and tyrosine. When EE cells cultivated under conditions of growth inhibition were diluted into fresh medium, immediate resumption of growth at the uninhibited rate occurred and persisted. On the other hand, when growth-inhibited EE cells were diluted into medium containing the same concentration of amino acid used in the first round of growth, an initial burst of uninhibited growth lasting about 24 h was followed by a drastic, progressively declining growth rate which deteriorated to cell death and lysis. When cells in stationary phase were used as an inoculum, as is done in typical growth characterizations with suspension cultures, the sensitivity to inhibition during the subsequent exponential growth phase was several-fold greater than was the case with EE cells. Hypotheses that growth inhibition might be caused by ammonia toxicity, keto-acid toxicity, or by inhibition of nitrate utilization were ruled out. Observations that provide new insight are: (i)growth-inhibited cells undergo drastic plasmolysis, (ii) L-glutamine is an effective antagonist of amino-acid inhibitors, and (iii) growth-inhibited cells exhibit a transient restoration of normal growth rate upon dilution into fresh growth medium. These results implicate a linkage of amino acids with osmotic regulation and nitrogen metabolism. 相似文献
35.
C. J. Rodrigues Jr. V. M. P. Varzea H. Hindorf Emilia F. Medeiros 《Journal of Phytopathology》1991,131(3):205-209
Strains of Colletotrichum isolated from berries of Coffea arabica from Angola and Malawi were identified as C. coffeanum causing coffee berry disease (CBD). The isolates were highly aggressive to berries of the cultivar ‘Catimor’ and produced high numbers of acervuli and extremely large masses of pink conidia when cultivated in the dark. These strains are apparently different in aggressiveness and morphology to those described in the past from Kenya. 相似文献
36.
Summary Mutations in an X-linked gene, gust-A, block the responses of Drosophila melanogaster to a group of pyranose sugars. It is shown that the behavioural effects of this mutation are correlated with a loss of electrical responses in taste receptors. The mutation affects the chemoacceptors for pyranose sugars leaving the furanose acceptors intact. 相似文献
37.
In vivo immunization of C57BL/6 mice with FBL-3, a syngeneic Friend-virus-induced leukemia, can induce a specific, T-cell-mediated cytotoxic response, as measured by the 125IUdR release assay. In vitro it was difficult to generate an analogous, primary cytotoxic response, using a normal spleen responder population. After modification of the splenic responders by adding normal peritoneal cells, this modified population then had the capacity to mount a primary cytotoxic response in the mixed-lymphocyte-tumor cell culture reaction to FBL-3. We have characterized the effector population as well as the helper (peritoneal) cells which were responsible for elevating the cytolytic response to FBL-3. The results indicate that there are at least two populations of cells which are essential for inducing a primary cell-mediated cytotoxic response. First, the effectors which are directly responsible for mediating the cytotoxic reactions and are derived from radiosensitive T cells and second, a helper cell population which is radioresistant and has the characteristics of macrophages. 相似文献
38.
Marta L. Silva Baltazar C Nuno S. Osrio Pedro N. S. Rodrigues Ana Raquel Maceiras Margarida Saraiva 《PLoS pathogens》2022,18(5)
Tuberculosis (TB), one of the deadliest threats to human health, is mainly caused by 2 highly related and human-adapted bacteria broadly known as Mycobacterium tuberculosis and Mycobacterium africanum. Whereas M. tuberculosis is widely spread, M. africanum is restricted to West Africa, where it remains a significant cause of tuberculosis. Although several differences have been identified between these 2 pathogens, M. africanum remains a lot less studied than M. tuberculosis. Here, we discuss the genetic, phenotypic, and clinical similarities and differences between strains of M. tuberculosis and M. africanum. We also discuss our current knowledge on the immune response to M. africanum and how it possibly articulates with distinct disease progression and with the geographical restriction attributed to this pathogen. Understanding the functional impact of the diversity existing in TB-causing bacteria, as well as incorporating this diversity in TB research, will contribute to the development of better, more specific approaches to tackle TB. 相似文献
39.
Aryel C. Goes Pepijn W. Kooij Laurence Culot Odair C. Bueno Andre Rodrigues 《Ecology and evolution》2022,12(7)
Leaf‐cutting ants and their fungal crops are a textbook example of a long‐term obligatory mutualism. Many microbes continuously enter their nest containing the fungal cultivars, destabilizing the symbiosis and, in some cases, outcompeting the mutualistic partners. Preferably, the ant workers should distinguish between different microorganisms to respond according to their threat level and recurrence in the colony. To address these assumptions, we investigated how workers of Atta sexdens sanitize their fungal crop toward five different fungi commonly isolated from the fungus gardens: Escovopsis sp., Fusarium oxysporum, Metarhizium anisopliae, Trichoderma spirale, and Syncephalastrum sp. Also, to investigate the plasticity of these responses toward recurrences of these fungi, we exposed the colonies with each fungus three times fourteen days apart. As expected, intensities in sanitization differed according to the fungal species. Ants significantly groom their fungal crop more toward F. oxysporum, M. anisopliae, and Syncephalastrum sp. than toward Escovopsis sp. and T. spirale. Weeding, self‐, and allogrooming were observed in less frequency than fungus grooming in all cases. Moreover, we detected a significant increase in the overall responses after repeated exposures for each fungus, except for Escovopsis sp. Our results indicate that A. sexdens workers are able to distinguish between different fungi and apply distinct responses to remove these from the fungus gardens. Our findings also suggest that successive exposures to the same antagonist increase hygiene, indicating plasticity of ant colonies'' defenses to previously encountered pathogens. 相似文献