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Biomedical subjects

L Perez

Publications and source records attributed to L Perez.

At least 55 records · Page 3Linked to original sources
PubMed1995

B cells capable of spontaneous IgG secretion in cerebrospinal fluid from patients with multiple sclerosis: dependency on local IL-6 production.

Cerebrospinal fluid (CSF) from multiple sclerosis (MS) patients contains B cells capable of spontaneous IgG secretion in vitro. This study analyses the function and regulation of these cells. CSF cells obtained from nine MS patients actively produced IgG during 2-3 days in culture, and the activity decreased when CSF cells were cultured in serum-free medium. CSF cells from four controls did not secrete detectable IgG in vitro. Further experiments revealed that IL-6 played a role on MS CSF IgG-secreting cells, as can be deduced from the following findings: (i) the addition of exogenous IL-6, but not of other cytokines, to serum-free cultures restored missing CSF cell IgG secretion (ii) the inclusion of anti-IL-6, but not of control, blocking MoAb reduced IgG secretion by CSF cells in fetal calf serum (FCS)-containing cultures; and (iii) CSF cells were capable of active IL-6 production in the presence of FCS. These results suggest that endogenous IL-6 production by MS CSF cells seems to be responsible for inducing CSF IgG-secreting B cells to reach terminal differentiation.

Adult↗
PubMed1994

Evidence for the involvement of macrophage-derived nitric oxide in the modulation of immune status by a conditioned aversive stimulus.

Prior work in our laboratory has demonstrated that exposure to a conditioned aversive stimulus developed through pairings with electric shock results in pronounced alterations of immune status. These conditioned alterations of immune status include a decreased in natural killer cell activity, decreased production of interleukin-2 and gamma-interferon by concanavalin A (ConA)-stimulated splenocytes and a profound suppression of the mitogenic responsiveness of T and B lymphocytes to mitogens. The present study examines the role of macrophage-derived nitric oxide in the conditioned stimulus-induced suppression of lymphocyte proliferation by measuring the level of nitrite accumulation in culture, determining the effect of macrophage depletion, and assessing the effect of NG-monomethyl-L-arginine (L-NMMA), a specific inhibitor of the L-arginine-dependent nitric-oxide synthesizing pathway, alone and in combination with L- or D-arginine. The results show that the conditioned suppression of the mitogenic responsiveness of splenocytes to ConA is accompanied by a marked increase in nitrite accumulation. Both the depletion of macrophages and the addition of L-NMMA attenuates the conditioned suppression of ConA-stimulated lymphocyte proliferation. Furthermore, the addition of excess L-arginine, but not D-arginine, counteracts the effect of L-NMMA. The present findings show that the neuroendocrine alterations induced by a conditioned aversive stimulus suppress lymphocyte proliferation through alteration of the production of nitric oxide by macrophages.

Animals↗
PubMed1994

Use of an air medical helicopter in a trauma prevention program.

Trauma is acknowledged as the leading cause of death in the United States in those under 45 years old, with the automobile being particularly lethal and costly. Preventive teaching is a component of any injury reduction program, and health care providers are becoming more actively involved in such efforts. The Mercy Air Ambulance medical team has developed a mock vehicle-collision demonstration, which is staged at area high schools shortly before graduation. The program is a joint effort of several agencies and services. It stimulates the arrest of the responsible driver, the rescue and subsequent air medical transport of two injured students and the death of a fourth student. Not only does this program educate the students in an entertaining fashion, but it results in valuable training for the multiple agencies and individuals who participate in the actual response to motor-vehicle collisions.

Accidents, Traffic↗
PubMed1994

The household structure of second-generation children: an exploratory study of extended family arrangements.

"Using data from the Children of Immigrants Survey, the antecedents of extended family arrangements among [U.S.] immigrant households with children are examined. The incidence and form of such arrangements, especially the presence of grandparents, are analyzed in relation to single parenthood, national origin, cultural assimilation, and socioeconomic variables. The findings serve to underscore the complexity of the correlates of extended family arrangements. While there is a relationship with single parenthood, more research is needed on the economic basis for the presence of relatives in the household. The analysis uncovered the need to also treat presence of grandparents as an independent variable, especially in the cultural assimilation of children of immigrants."

Acculturation↗
PubMed1993

Ablation of irreversibly rejected renal allograft by embolization with absolute ethanol: a new clinical application.

Surgical allograft nephrectomy has been the conventional therapy for removing failed kidney allografts when clinical manifestations of graft intolerance appear. However, removal of a transplanted kidney is an extensive surgical procedure. On the other hand, transcatheter vascular embolization (TVE) has proven useful in ablating organs and could be applied to renal transplant ablation. The aim of this study was to present the results of TVE for the treatment of graft intolerance syndrome (GIS) in failed allograft kidneys. Transcatheter vascular embolization was performed in 14 allograft recipients (33 +/- 13 years of age; 10 men and four women) affected by GIS after irreversible kidney allograft failure. Graft intolerance syndrome was diagnosed by fever (93%), hematuria (50%), graft pain (36%), flu-like symptoms (29%), and increased graft size (29%). Absolute ethanol (0.1 mL/kg body weight) was injected in the allograft artery, and in seven patients a stainless steel coil was left in the renal artery following ethanol injection. All patients showed clinical disappearance of the GIS. No major complication occurred, although a postembolization syndrome of pain, fever, hematuria, numbness, and paresthesia of the affected area appeared in 11 of the 14 patients. After 2 to 56 months of follow-up no late complications occurred, with the exception of a graft abscess formation in one patient after 6 months of embolization. Subsequent transplantectomy was uneventful. In conclusion, TVE is a safe and effective method for kidney graft ablation, and it may become an alternative treatment for GIS following irreversible rejection.

Adult↗
PubMed1992

Involvement of membrane traffic in the replication of poliovirus genomes: effects of brefeldin A.

Brefeldin A (BFA) is a macrolide antibiotic that has multiple targets in vesicular transport and blocks membrane traffic between the cis- and trans-Golgi compartments, leading to the disruption of the trans-Golgi apparatus (for a review see Pelham, 1991, Cell 67, 449-451). Consequently, BFA interferes with the maturation of viral glycoproteins and suppresses the formation of infectious viruses that contain a lipid envelope. We report that this antibiotic strongly inhibits poliovirus replication even though this virus lacks a lipid envelope and does not encode any glycoproteins. Addition of BFA from the beginning of poliovirus infection blocks the synthesis of late proteins but has no effect on p220 cleavage, indicating that the input viral RNA is translated to produce active 2Apro. The presence of BFA at later times has no effect on poliovirus protein synthesis, indicating that this step is not a direct target for the antibiotic. Indeed, the target of BFA is viral RNA synthesis, because addition of the antibiotic at any time after poliovirus infection drastically reduces the incorporation of labeled uridine into poliovirus RNA. Both plus- and minus-stranded RNA syntheses are diminished when BFA is present from the beginning of infection, but plus-stranded RNA synthesis is more affected when the inhibitor is added at later times. The replication of poliovirus RNA takes place in close association with membrane vesicles that fill the cytoplasm of the infected cells. Little is known about the origin and function of these vesicles that form part of the viral replication complexes. Our findings suggest that the replication of poliovirus genomes may require the maturation of membranous vesicles from a vesicular compartment that is affected by BFA. The effects of BFA on late protein synthesis by other animal viruses varies according to the virus species examined. Among picornaviruses, rhinoviruses are sensitive to the antibiotic, whereas encephalomyocarditis virus is resistant. A negative-stranded RNA virus such as vesicular stomatitis is blocked by BFA, whereas vaccinia virus, a cytoplasmic DNA virus, is resistant.

Antiviral Agents↗
PubMed1991

Synthesis of Semliki Forest virus RNA requires continuous lipid synthesis.

The involvement of lipid biosynthesis in the replication of Semliki Forest virus (SFV) in HeLa cells has been analyzed by the use of cerulenin, an inhibitor of lipid synthesis. The presence of this agent from the beginning of infection blocks the appearance of viral proteins. However, when the antibiotic is added at later stages of infection it has no effect on protein synthesis, the cleavage of viral proteins and their acylation by palmitic acid. Cerulenin is a powerful inhibitor of viral RNA synthesis, as analyzed by [3H]uridine incorporation, incorporation of [32P]phosphate into viral replication complexes, or Northern blot analysis of viral RNAs hybridized with minus- or plus-stranded riboprobes. Finally, analysis of phospholipids made in SFV-infected cells indicates that viral infection clearly stimulates the synthesis of phosphatidyl choline and modifies the membrane formed as analyzed by sucrose gradient centrifugation. Cerulenin blocks the synthesis of phospholipids and inhibits the formation of new membranes. These results show that, when the synthesis of lipids is blocked by cerulenin, SFV RNA replication is hampered, suggesting that the synthesis of viral RNAs needs continuous lipid synthesis and membrane formation.

Centrifugation, Density Gradient↗
PubMed1991

The role of steroids in reproduction in female elasmobranchs and reptiles.

Adequate evidence exists to suggest the importance of temporal changes in steroid hormone ratios in the normal reproductive/vitellogenin cycle in oviparous and viviparous elasmobranchs and reptiles. In oviparous species, where the cycle is relatively short, secretion of gonadal hormones is synchronous; thus inhibitory actions of progesterone (P) on hepatic or reproductive tract functions would be offset by stimulatory actions of estradiol (E), resulting in appropriate vitellogenin secretion and reproductive tract development. In viviparous species, temporal asynchrony of E and P secretion occurs, and the actions of the individual hormones can be more easily dissected out. Thus, during gestation, where P is the dominant hormone, antagonistic or stimulatory actions of E may be prevented, and the inhibitory action of P on vitellogenesis dominant. Hence vitellogenesis is limited to the follicular phase and eggs are retained. Although the elasmobranch and reptilian species discussed here do not form a continuum through phylogenesis, but rather are extant forms of a particular line of evolution, it is possible to extrapolate from these observations to the probable endocrine interactions in a species as viviparity evolves from oviparity. The theoretical intermediate stage would involve; (a) egg retention, (b) extension of the luteal phase and increased P secretion and (c) resulting in E/P asynchrony and potential expression of "independent" P action, egg retention and yolk suppression.

Animals↗
PubMed1990

Vitellogenesis in reptiles as a model for mammalian sex-differentiated hepatic protein synthesis.

The stimulation of yolk protein synthesis by estrogen is a characteristic of female non-mammalian vertebrates; in mammals, or their reptilian ancestors, however, vitellogenesis has been suppressed as a corollary of the evolution of viviparity. It is our hypothesis that progesterone has a dual role in this phylogenetic trend: a) to inhibit myometrial contraction and thus set the stage for internal development of embryos and associated placentation and b) to inhibit yolk protein synthesis in a coordinate manner as placentation became an efficient direct supply of nutrients to the fetus. Despite the absence of vitellogenesis per se in eutherian mammals, significant sex-differentiated hepatic protein-lipid synthetic functions remain, which are under complex hormonal control. We have presented evidence that in the reptiles, the central vertebrate group from which the ancestors of modern mammals evolved, the control of yolk protein synthesis is also complex, involving both pituitary hormones (GH, PRL, and LH) and ovarian steroids (estradiol, testosterone, and progesterone). Adequate evidence exists to suggest that mammalian hepatic lipoprotein synthesis and its regulatory elements are phylogenetically derived from their reptilian ancestors and may be better understood in this context. This is of particular relevance to cardiovascular disease in which there is a clear sex bias yet for which no coordinated research program exists which takes into account the relevant phylogenetic history. We believe that reptilian, and possibly avian, models could be used to great advantage to probe the endocrine components of cardiovascular disease.

Animals↗
PubMed1990

Production and characterization of human gamma interferon from Escherichia coli.

The production of human gamma interferon as intracellular inclusion bodies in Escherichia coli, which simplified the purification process, is described. An expression plasmid carrying lipoprotein and the tryptophane promoters in tandem was used. Preparation of highly pure interferon was achieved using high resolution chromatography after denaturation and renaturation steps. Structural characteristics of this protein were verified by mass spectrometric analysis. Additional control tests have shown the suitability of the final product for clinical purposes.

Amino Acid Sequence↗
PubMed1990

Lipophosphoglycan and secreted acid phosphatase of Leishmania tropica share species-specific epitopes.

Several species-specific monoclonal antibodies (T11, T13-T15) which only react with Leishmania tropica, recognize phosphorlated carbohydrate epitopes on lipophosphoglycan and the structurally related molecule, phosphoglycan, which is shed by promastigotes into spent culture medium. During immunoaffinity isolation of [32P]orthophosphate-labeled phosphoglycan on monoclonal antibody T15 conjugated to Sepharose 4B, a high-Mr component (approx. 200,000) was co-purified. The latter material is metabolically labeled with [35S]methionine and [3H]glucosamine. This glycoprotein was separated from phosphoglycan by chromatography on lentil lectin resin. The glycoprotein exhibited a L-tatrate-sensitive acid phosphatase activity, typical of secreted acid phosphatase (EC 3.1.3.2) from Leishmania. Monospecific antibodies to Leishmania donovani-secreted acid phosphatase selectively precipitated the L. tropica enzyme from immunoaffinity purified mixtures of the two antigens, and monoclonal antibodies to lipophosphoglycan precipitate the pure enzyme. Species-specific monoclonal antibodies to L. major lipophosphoglycan also recognized both L. tropica antigens. Treatment of the acid phosphatase with periodate or phosphodiesterase I abolished binding by the monoclonal antibodies to the pure enzyme. These results demonstrate that the two major secreted glycoconjugates of Leishmania tropica, the lipophosphoglycan and the acid phosphatase, share species-specific phosphorylated carbohydrate epitope(s).

Acid Phosphatase↗
PubMed1990

Vertebrate vitellogenesis: molecular model for multihormonal control of gene regulation.

The stimulation of yolk protein synthesis by estrogen is a characteristic of female non-mammalian vertebrates; in mammals, however, vitellogenesis has been suppressed as a corollary of the evolution of viviparity. It is our hypothesis that progesterone has a dual role in this phylogenetic trend; a) to inhibit myometrial contraction and thus set the stage for internal development of embryos and associated placentation, b) to inhibit yolk protein synthesis as placentation became an efficient direct supply of nutrients to the fetus. We have presented evidence that in the reptiles, the central vertebrate group from which the ancestors of modern mammals evolved, the control of yolk protein synthesis is complex, involving both pituitary and ovarian steroids (estradiol, testosterone and progesterone). This system provides an excellent model for the multihormonal contents of gene regulation involving both + and - controls.

Animals↗
PubMed1989

Mineral phases of calcium phosphate.

Many studies of calcium phosphate precipitation have been made using relaxation techniques in which the concentrations of the lattice ions are allowed to decrease as equilibrium is approached. Since the nature of the phases that form depend markedly on the solution composition, this decrease can lead to concomitant phase transformations during the crystallization experiments. The results of the present constant composition (CC) studies show that defect apatites may be formed under conditions of sustained supersaturation with a non-stoichiometric coefficient dependent on the pH of the growth medium. An important factor in analyzing these experiments is the initial surface modification and ion-exchange processes involving H+ and Ca2+ ions after inoculation of the supersaturated solutions. Thereafter, active growth sites may be eliminated as the crystals undergo lattice perfection. Transformation of dicalcium phosphate dihydrate to octacalcium phosphate, involving dissolution and subsequent nucleation and growth of the new phase, is also influenced by surface roughening of the initial phase. Typical inhibitors that reduce the rate of growth of seed crystals in supersaturated solutions may actually induce the nucleation of calcium phosphate phases when immobilized on inert surfaces. This may be a factor in the modulation of crystal growth in many biological systems.

Calcium Phosphates↗
PubMed1989

The dual role of polyelectrolytes and proteins as mineralization promoters and inhibitors of calcium oxalate monohydrate.

Polyelectrolytes and protein molecules appear to be able to act not only as crystallization inhibitors when present in solution, but also as promoters of crystal growth when immobilized onto surfaces. Because this is especially relevant for systems in which heterogeneous nucleation can occur, the influence of poly-L-glutamic (PGlu) acid, poly-L-aspartic (PAsp) acid, and human serum albumin (HSA) on the nucleation and growth inhibition of calcium oxalate monohydrate (COM) was studied using the Constant Composition (CC) kinetics technique. The overgrowth of COM on hydroxyapatite (HAP) seed crystals pretreated with HSA was also investigated. Pronounced differences in inhibiting and nucleating potential were found for the various additives. HSA, a relatively poor growth inhibitor when present in solution, was found to nucleate very regular, hexagonal COM crystals when immobilized on a surface and to enhance the overgrowth of COM when adsorbed on HAP surfaces.

Calcium Oxalate↗
PubMed1989

Bombesin produces hypothermia in insulin treated rats.

Previous studies have shown that central injection of bombesin produces hypothermia in food-deprived, but not food satiated rats at normal ambient temperatures. The present study evaluated the effects of bombesin on core body temperature (Tb) and feeding behavior in rats pretreated with insulin. Administration of bombesin (0.25, 0.5, and 1.0 microgram) into the lateral cerebral ventricle produced hypothermia in rats injected with insulin (10 U/kg; i.m.). No significant change in core temperature was observed in control rats following bombesin. Insulin treatments significantly stimulated feeding behavior and the highest dose of bombesin significantly reduced feeding behavior. The results demonstrate bombesin-induced hypothermia under metabolic conditions similar to acute starvation. These findings are consistent with the hypothesis that bombesin-induced hypothermia in food-deprived rats is directly related to the fasting state.

Animals↗
PubMed1989

Biologicals production by recombinant DNA technology in Cuba.

During 1981 we started an intensive programme for the development of biotechnology in Cuba. The first project was related to the production of leucocyte interferon and the cloning an expression of these genes in prokaryotic and yeast cells. These products are currently obtained in large amounts and their physical and chemical characterization are presented. The use of mammalian cells in culture for the production of recombinant proteins has also been carried out. The results obtained with the expression and amplification of the hepatitis B surface antigen (HBsAg) in CHO cells are discussed and compared with that obtained in yeast. The construction of a recombinant vaccinia virus carrying the HBsAg was also achieved. The specific transcripts were characterized and the Ab levels tested in animals. The results presented here indicate that the host system is a very important aspect to be taken into consideration and in some cases mammalian cells appear to be the best choice.

Animals↗