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Biomedical subjects

R A Silva

Publications and source records attributed to R A Silva.

At least 37 records · Page 2Linked to original sources
PubMed2000

Minor role played by type I tumour necrosis factor receptor in the control of Mycobacterium avium proliferation in infected mice.

Control of mycobacterial growth depends on the concerted activity of different cytokines acting in different stages of the development of innate and adaptive immune responses. Tumour necrosis factor-alpha (TNF-alpha) has been shown to play a protective role in Mycobacterium avium infections. Here we assessed the growth of this mycobacterial species in wild-type mice and in mice with a genetically engineered disruption of the type I receptor for TNF-alpha (p55-KO mice). p55-KO mice infected with a low-virulence strain of M. avium exhibited a slightly delayed capacity to eliminate the micro-organisms from the liver as compared with wild-type animals. However, either the growth of this strain in the other organs studied (spleen and lung) or the growth of two other strains of M. avium with intermediate or high virulence, failed to be affected by mutation of the TNF-alpha receptor. p55-KO mice were also as protected by the administration of recombinant interleukin-12 as the heterozygous p55 +/- mice. We conclude that signalling through the type I TNF receptor plays a small role in vivo in the induction of mycobacteriostasis during M. avium infection but may improve survival during infection with virulent mycobacteria, independently of the extent of their proliferation.

Animals↗
PubMed2000

Effects of interleukin-12 in the long-term protection conferred by a Mycobacterium avium subunit vaccine.

The effects of the addition of recombinant interleukin (IL)-12 to a mycobacterial subunit vaccine were analyzed in terms of the longevity of the protective immunity generated. BALB/c mice were immunized with culture filtrate proteins from Mycobacterium avium with dimethyl-dioctadecilammonium bromide (DDA) as an adjuvant. This subunit vaccine induced protection against a challenge by M. avium which lasted for at least 6 months while waning with time until 1 year postvaccination. Whereas the addition of IL-12 enhanced the initial protective efficacy of this subunit vaccine during the first 6 months, it accelerated the loss of protective efficacy observed at 1 year postvaccination. These data confirm the adjuvant properties of IL-12 in vaccines against mycobacteria and raise the possibility of late counter-protective untoward effects.

Adjuvants, Immunologic↗
PubMed2000

Animal trypanosomiasis in South America. Current status, partnership, and information technology.

Animal trypanosome species of economical importance in South America include T. vivax and T. evansi. Both species are described in Brazil, Bolivia, Colombia, French Guyana, Peru, Suriname, and Venezuela. In Argentina and Guyana, only T. evansi and T. vivax are found, respectively. Our studies on T. vivax indicated that the parasite was spreading around 1.3 km per day in Bolivia. We found severe leukopenia in bovines from Pantanal (Brazil) and the Department of Santa Cruz (Bolivia). Because it can cause immunosuppression, the importance of trypanosomiasis control in ensuring success of vaccination campaigns against foot and mouth disease (FMD) in the Pantanal and Bolivia should be considered. The use of one needle for several animals during FMD campaigns in Brazil and Bolivia could also contribute to the spread of T. vivax. The anticipated losses due to T. vivax could exceed $160 million, assuming there are 11 million head of cattle in the Brazilian Pantanal and Bolivian lowlands. International collaboration among research institutes is needed to deal with these diseases and parasites. Previous efforts using information technologies resulted in the creation of two discussion lists (Tryplink and Trypan), the edition of the on-line version of Trypnews and Internet conferences.

Animals↗
PubMed2000

Molecular and morphological studies of Brazilian Trypanosoma evansi stocks: the total absence of kDNA in trypanosomes from both laboratory stocks and naturally infected domestic and wild mammals.

The kinetoplast DNA (kDNA) minicircle molecules of 14 Brazilian stocks of Trypanosoma evansi were studied by morphological approaches (Giemsa and 4'-6'-diamidino-2-phenylindole staining and transmission electron microscopy) and molecular approaches (probing with an oligonucleotide complementary to the minicircle origin of replication and polymerase chain reaction amplification of a minicircle sequence). All methods indicated the absence of both a typical kinetoplast and kDNA minicircles, even in a very small number of parasites of a single stock or in small numbers of copies of molecules per cell. We did not detect any altered kDNA molecules. There were no kDNA molecules in either old or new stocks of T. evansi maintained by successive passages in mice. Similarly, no kDNA minicircles were detected in trypanosomes in blood smears from naturally infected domestic and wild animals. Thus, the total absence of kDNA in Brazilian stocks of T. evansi from both domestic and wild mammals is probably the natural state of Brazilian T. evansi.

Animals↗
PubMed1999

Beta-hairpin stabilization in a 28-residue peptide derived from the beta-subunit sequence of human chorionic gonadotropin hormone.

The beta-subunit of the human chorionic gonadotropin (hCG) hormone, which is believed to be related to certain types of cancer, contains three hairpin-like fragments. To investigate the role of beta-hairpin formation in the early stages of the hCGbeta folding, a 28-residue peptide with the sequence RDVRFESIRLPGSPRGVNPVVSYAVALS, corresponding to the H3-beta hairpin fragment (residues 60-87) of the hCGbeta subunit, was studied under various conditions using three optical spectroscopic methods: Fourier transform ir spectroscopy, electronic CD, and vibrational CD. Environmental conditions are critical factors for formation of secondary structure in this peptide. TFE : H(2)O mixed solvents induced helical formation. Formation of beta-structure in this peptide, which may be related to the native beta-hairpin formation in the intact hormone, was found to be induced only under conditions such as high concentration, high temperature, and the presence of nonmicellar sodium dodecyl sulfate concentrations. These findings support a protein folding mechanism for the hCGbeta subunit in which an initial hydrophobic collapse, which increases intermolecular interactions in hCGbeta, is needed to induce the H3-beta hairpin formation.

Amino Acid Sequence↗
PubMed1999

Unidirectional rotary motion in a molecular system.

The conversion of energy into controlled motion plays an important role in both man-made devices and biological systems. The principles of operation of conventional motors are well established, but the molecular processes used by 'biological motors' such as muscle fibres, flagella and cilia to convert chemical energy into co-ordinated movement remain poorly understood. Although 'brownian ratchets' are known to permit thermally activated motion in one direction only, the concept of channelling random thermal energy into controlled motion has not yet been extended to the molecular level. Here we describe a molecule that uses chemical energy to activate and bias a thermally induced isomerization reaction, and thereby achieve unidirectional intramolecular rotary motion. The motion consists of a 120 degrees rotation around a single bond connecting a three-bladed subunit to the bulky remainder of the molecule, and unidirectional motion is achieved by reversibly introducing a tether between the two units to energetically favour one of the two possible rotation directions. Although our system does not achieve continuous and fast rotation, the design principles that we have used may prove relevant for a better understanding of biological and synthetic molecular motors producing unidirectional rotary motion.

Models, Molecular↗
PubMed1999

Hematology of natural bovine trypanosomosis in the Brazilian Pantanal and Bolivian wetlands.

We report hematological changes observed in natural cases of bovine trypanosomosis due to Trypanosoma vivax in beef and dairy cattle from Bolivian wetlands and Pantanal, Brazil. The main hematologic changes produced by T. vivax infections were anemia and severe leucopenia. The cattle presented macrocytic hypochromic anemia. The leukocyte changes were characterized by relative lymphocytosis and monocytosis and decrease in the neutrophil counts. The clinical signs were lachrymation, progressive weakness, marked weight loss, inappetence, diarrhea and abortions during the third trimester of pregnancy.

Abortion, Veterinary↗
PubMed1999

Argon plasma coagulation therapy for hemorrhagic radiation proctosigmoiditis.

BACKGROUND: Radiation-induced proctosigmoiditis is a serious complication of pelvic radiation therapy. Rectal bleeding occurs among 6% to 8% of these patients and is extremely difficult to manage. Pharmacotherapy is generally ineffective, whereas surgical treatment is associated with high morbidity and mortality. Argon plasma coagulation is a new method of noncontact electrocoagulation well suited for hemostasis of large bleeding areas. METHODS: From December 1996 through March 1998, we used argon plasma coagulation to treat 28 patients with hemorrhagic radiation-induced proctosigmoiditis. Indications for treatment were anemia (n = 18) and persistent bleeding despite pharmacotherapy (n = 10). Argon flow and electrical power were set at 1.5 L/min and 50 W. The severity of rectal bleeding was graded from 0 to 4 (highest), and hemoglobin levels were recorded before and after treatment. RESULTS: Eighty-two therapeutic sessions were performed (median 2.9 sessions per patient). The severity score for rectal bleeding dropped at least 1 point for all but 2 patients, and the mean value decreased from 2.96 to 0.68. Average hemoglobin level increased 1.2 gm/dL (1.9 gm/dL among anemic patients). No serious complications were observed. CONCLUSIONS: Argon plasma coagulation appears to be a simple, safe, and effective technique in the management of hemorrhagic radiation-induced proctosigmoiditis.

Adult↗
PubMed1999

Vibrational circular dichroism spectroscopy of selected oligopeptide conformations.

Vibrational circular dichroism (VCD) has been shown to be a useful technique for characterization of the qualitative secondary structure type for linear polypeptides and oligopeptides. A brief review of characteristic spectral responses and applications is given. Since VCD is dependent on relatively short range interactions, it detects residual structure in such oligomers even if long range order is lost. VCD studies presented here for Lys oligomers as well as Lys and Glu polymers as a function of length, salt added and temperature, confirm residual local order in these 'random coils'. Comparison to results with Pro oligomers, supports an interpretation that these extended structures have a left handed twist conformation. The 'coil' VCD is shown to be significantly reduced in intensity by temperature increase and by decrease in peptide length. By contrast, for partially alpha-helical Ac-(AAKAA)3GY-NH2 oligomers, the spectrum changes to the high temperature Lys(n) shape on heating, first losing then gaining intensity, indicating an equilibrium shift between structured states, from helix to coil (locally ordered) forms. VCD is shown to be a useful technique for monitoring local order in otherwise random coil structures.

Amino Acid Sequence↗
PubMed1999

Resistance of virulent Mycobacterium avium to gamma interferon-mediated antimicrobial activity suggests additional signals for induction of mycobacteriostasis.

The cytokine gamma interferon (IFN-gamma) plays a major role in the control of Mycobacterium avium infections. We assessed whether the progressive growth of virulent strains of M. avium was associated with alterations in the production of this cytokine as evaluated by reverse transcription-PCR and detection of immunoreactive cytokine in the serum and in spleen homogenates. We found that IFN-gamma was induced during infection by a virulent strain of M. avium to similar or even higher extents than the levels found during infections by a less virulent strain whose growth was controlled. IFN-gamma produced during infection by both mycobacterial strains was partly derived from T cells and led to activation of macrophages, namely, those that were infected. Concomitant with the development of the infection with the virulent strain of M. avium there was an extensive depletion of lymphocytes in the spleen. Thymectomy alone promoted the proliferation of the virulent, but not of the less virulent, strain of M. avium. Our data indicate that virulent strains of M. avium resist the antimicrobial mechanisms of IFN-gamma-activated macrophages and raise the possibility that a second, T-cell-dependent signal is required for the effective control of mycobacterial replication inside macrophages.

Animals↗
PubMed1998

Evaluation of IL-12 in immunotherapy and vaccine design in experimental Mycobacterium avium infections.

IL-12 is a pivotal cytokine in the induction of IFN-gamma-mediated protective immune responses. We tested the effects of rIL-12 administration to Mycobacterium avium-infected mice and found a limited ability to induce protection against the infection; this ability varied according to the mycobacterial strain studied. IL-12 accelerated the expression and production of IFN-gamma in both immunocompetent and immunodeficient SCID or CD4-depleted mice. Evidence of NK cell activation was found as well as an enhancement of the ability to adoptively transfer resistance with T cell-enriched spleen cell populations and an increase in inflammatory cell recruitment in the liver. The protective ability of IL-12 was dependent upon the endogenous production of IFN-gamma as evaluated by the use of specific neutralizing Abs or IFN-gamma gene-disrupted mice. IL-12 potentiated the protective immunity conferred by a subunit vaccine containing M. avium culture filtrate proteins and dimethyl dioctadecyl ammonium chloride as an adjuvant. Thus, we show limited immunotherapeutic benefits from IL-12 administration in M. avium infections and promising results in its use as a coadjuvant in vaccine design.

Adjuvants, Immunologic↗
PubMed1998

Outbreaks of trypanosomosis due to Trypanosoma vivax in cattle in Bolivia.

This paper reports the first occurrence of bovine trypanosomosis due to Trypanosoma vivax in Bolivia. T. vivax was identified in thin blood smears of 159 cattle from the Provinces of Velaco (57), Nuflo de Chavez (20), Guayaros (30) and Chiquitos (52), and in 86.20% of 29 cattle from Laguna Concepción examined by microhematocrit test. The clinical signs observed were fever, anemia, abortion, progressive weakness, loss of appetite, lethargy, substantial weight loss in a relatively short time, and progressive emaciation.

Abortion, Veterinary↗
PubMed1998

Biometrical alterations of Trypanosoma evansi isolate in laboratory rodents.

Biometrical alterations in a horse Trypanosoma evansi isolate were observed when passaged in laboratory rodents. The major parasite transformation observed was the increase in the total length as a consequence of an increase in some parasite measurements. These transformations probably occurred as a consequence of a host change from horse to rodents. No kinetoplastic forms were observed.

Animals↗
PubMed1998

Analysis of T cells recruited during delayed-type hypersensitivity to purified protein derivative (PPD) versus challenge with tuberculosis infection.

The delayed-type hypersensitivity (DTH) to purified protein derivative (PPD) test has been used to infer about protective immunity to Mycobacterium tuberculosis and to diagnose tuberculosis. We showed that in memory tuberculosis-immune mice both DTH to PPD and resistance to M. tuberculosis could be effectively elicited in the footpad and both reactions led to the accumulation of reactive T cells in the regional lymph nodes with a CD4+ phenotype and characterized by the secretion of high levels of interleukin-2 (IL-2) and interferon-gamma (IFN-gamma) and no IL-4. By adoptive transfer into nude mice of highly purified CD4+ T cells harvested during the recall of protective immunity it was confirmed that this population mediated both manifestations. However, the specificity of the T cells recruited during these processes were found to differ markedly; T cells involved in protection to a challenge with live tuberculosis bacilli recognized predominantly low-mass culture filtrate antigens below 15 000 MW, while cells recruited during DTH to PPD were directed to molecular mass fractions between 15 000 and 31 000. Using single purified antigens we showed that the latter cells recognized the secreted mycobacterial protein Ag85B and the heat-shock proteins, DnaK and GroEL. Protective T cells, in contrast, were characterized by a very high frequency of T cells directed to the ESAT-6 peptide 1-20.

Acyltransferases↗
PubMed1997

Electrochemical and surface modifications on N+-ion-implanted 316 L stainless steel.

The effect of nitrogen-ion implantation on the electrochemical behaviour of 316 L stainless steel in a simulated physiological solution (HBSS-Hank's Balanced Salt Solution) was studied by open-circuit potential versus time and cyclic polarization techniques, with the aim of characterizing the surfaces and choosing the best nitrogen-ion fluence. Three fluences (10(15), 10(16) and 10(17) ions/cm2) were used. The 10(16) ions/cm2 N+ fluence improves the corrosion resistance of the 316 L stainless steel.

Journal Article↗
PubMed1996

Met-Lys-bradykinin-Ser, the kinin released from human kininogen by human pepsin.

This study was carried out to show the site in kininogen, using synthetic substrates, that is cleaved by a purified human pepsin component with a molecular weight of 35,000 daltons. The study used 4 (four) intramolecularly quenched fluorogenic substrates containing N- and C-terminal sequences around the methionyl-lysyl-bradykinin (MLBK) region of kininogen: Abz-LMKRP-Eddnp, Abz-MISLMKRP-Eddnp, Abz-FRSSR-Eddnp and Abz-RPPGFSPFRSSRQ-Eddnp. The hydrolysis on N-terminal sequences Abz-LMKRP-Eddnp and Abz-MISLMKRP-EDDnp occurred at L-M linkage and on C-terminal sequences Abz-FRSSR-Eddnp, and Abz-RPPGFSPFRSSRQ-Eddnp occurred at S-S linkage. The released peptide Abz-RPPGFSPFRS was able to contract rat uterus muscle. The results suggest that Met-Lys-Bradykinin-Ser, should be the peptide released from human kininogen by a purified human pepsin component.

Amino Acid Sequence↗
PubMed1995

Endogenously produced IL-12 is required for the induction of protective T cells during Mycobacterium avium infections in mice.

Immunity to Mycobacterium avium depends on the induction of protective CD4+ T cells. In mice, M. avium induces a Th1 response leading to protective immunity dependent on IFN-gamma and TNF. In this study, we analyzed whether endogenously produced IL-12 was involved in the generation of such protective T cells. We found that the neutralization of IL-12 with the administration of specific mAbs throughout the course of the infection led to the inability of BALB/c mice to control the infection by M. avium strain 2447. On the contrary, the late neutralization of IL-12, with the administration of the mAb starting only at the third week of infection, did not affect the growth of M. avium. The neutralization of IL-12 blocked the induction of protective T cells detected upon adoptive transfer to sublethally irradiated recipient mice. The neutralization of IL-12 in the recipient mice did not affect the protective activity of immune cells, showing that IL-12 is involved mainly in the induction, and not the expression, of acquired cell-mediated immunity. IL-12 was also shown to be required for a T cell-independent pathway of resistance present in T cell-deficient severe combined immunodeficient (SCID) mice. Finally, animals whose IL-12 was blocked expressed heightened levels of IL-4 and IL-10 message and reduced expression of IFN-gamma as compared with control mice.

Animals↗