PubMed Health⌕ Search

Biomedical subjects

S G Li

Publications and source records attributed to S G Li.

At least 37 records · Page 2Linked to original sources
PubMed1996

Density, survival and dispersal of Anopheles gambiae complex mosquitoes in a west African Sudan savanna village.

To obtain information on adult populations of Afrotropical malaria vector mosquitoes, mark-release-recapture experiments were performed with Anopheles females collected from indoor resting-sites in a savanna area near Ouagadougou, Burkina Faso, during September 1991 and 1992. Results were used to estimate the absolute population densities, daily survival rates, and dispersal parameters of malaria vectors in that area. In 1991 a total of 7260 female Anopheles were marked and released, of which 106 were recaptured in the release village and 6 in the neighbouring villages, a total recapture rate of 1.5%. The following year 13,854 female Anopheles were released and 116 recaptured in Goundri and 8 in the neighbouring villages, a total recapture rate of 0.9%. Recaptures were found in three of eight villages near Goundri. Nearly all of the recaptured mosquitoes were An gambiae s.l. Of these, molecular determination revealed that An.gambiae s.s. and An.arabiensis were present in a ratio of approximately 2:3. Two simple random models of dispersal were simulated and the parameters of the models determined by searching for the least-squared fit between simulated and observed distributions. The mean distance moved by individual mosquitoes, estimated in this way, ranged 350-650 m day-1, depending on the model and the year considered. Population densities were estimated using the Lincoln Index, Fisher-Ford and Jolly's methods. The estimates of population size had high standard errors and were not particularly consistent A "consensus' value of 150,000-350,000 mosquitoes is believed to apply for the An.gambiae s.l. female population. Survival was estimated to be 80-88% per day.

Animals↗
PubMed1995

[Elimination effect of ethyl alcohol on the DCCD-induced inhibition of hydrolytic activity of H+-ATPase complex].

12.5% ethyl alcohol was added into the reaction system containing mitochondrial H(+)-ATPase complex of pig heart, which was preincubated with 0.5 microgram/ml DCCD dicyclohexylcarbodiimide) at 30 degrees C. Or the DCCD and ethyl alcohol were simultaneously incubated with H(+)-ATPase at 30 degrees C. In either case, the inhibition of the hydrolytic activity of H(+)-ATPase caused by DCCD could be completely eliminated in the presence of ethyl alcohol. If methyl alcohol was instead of ethyl alcohol, the DCCD inhibition could only be partly eliminated. In the replacement of ethyl alcohol by dimethyl sulfoxide, no elimination could be observed. After preincubation of 2 micrograms/ml oligomycin with H(+)-ATPase complex instead of DCCD, the same concentration of ethyl alcohol could not caused elimination effect, which indicates no un-coupling effect happened by ethyl alcohol. The kinetic experimental result showed that ethyl alcohol exhibits non-competitive inhibition to the hydrolytic activity of H(+)-ATPase complex. It was deduced that ethyl alcohol could result in conformational change of F1 of the complex, such as to affect the activity of the enzyme. The measurement of DPH (diphenylhexatriene) fluorescence polarization, the fluorescence labelled with N-(1-pyrenyl) maleimide and intrinsic fluorescence of H(+)-ATPase complex compared with control show that the three cases, i.e. only treated with DCCD, only treated with ethyl alcohol or treated with DCCD and ethyl alcohol, appear different conformations of H(+)-ATPase complex. But the conformation caused by DCCD and ethyl alcohol was more like that by ethyl alcohol. This is consistent with results obtained from activity of DCCD plus ethyl alcohol and only ethyl alcohol. These results mentioned above indicate that the mechanism of ethyl alcohol eliminating the DCCD-induced inhibition of H(+)-ATPase is a conformational interaction caused by DCCD and ethyl alcohol.

Animals↗
PubMed1994

Product-activation of Escherichia coli membrane-bound H(+)-ATPase (F1F0-ATPase) connected with epsilon-subunit at alkaline pH.

Mutant strain AN1518 or AN2387 (Gly48-->Asp in epsilon-subunit) and partial revertant strain AN2540 (Gly48-->Asp, Pro47-->Ser in epsilon-subunit) of E. coli were used in a kinetic study of membrane-bound H(+)-ATPase. It was found that at pH 9.0 mutant strain AN1518 or AN2387 and partial revertant strain AN2540 gave a low initial rate, which increased with time until linearity was reached after 1-2 min. This phenomenon was prominent in mutant strains, but was not so obvious in wild-type AN346 of E. coli; this property is similar to F1-ATPase reported by Cox [1]. The mechanism of the slow activation of membrane-bound H(+)-ATPase was further investigated in this paper. The experimental results indicated that the hydrolytic rate of E. coli F1F0-ATPase that increased with time was membrane protein concentration- and pH-dependent, and that the product ADP produced during ATP hydrolysis is the factor causing the slow activation. Preincubation of the hydrolytic product ADP with a concentration comparable to that produced in the assay (20 microM) caused initial activation of ATP hydrolysis and abolished the slow activation. On the other hand, with the removal of ADP during the progress of the hydrolytic reaction it could be seen that the slow activation was abolished as well. In order to test the relationship between the epsilon-subunit and ADP involved in the slow activation, trypsin treatment was carried out on the membrane-bound H(+)-ATPase of various strains. The activation observed after trypsin treatment was on the order of AN1518 > AN2540 > AN346. The activation effects of ADP and trypsin were not found to be additive. This implies that ADP acted in a similar way to trypsin, i.e., to cause removal of the epsilon-subunit. A tentative mechanism of the slow activation was proposed that ADP, a product of ATP hydrolysis, could induce conformational changes of F1F0 at alkaline pH 9.0, thus weakening the binding strength between the epsilon-subunit and other subunits of F1F0, and resulting in removal or partial removal of the epsilon-subunit. This further impaired the coupling of F1 and F0 in the mutant strains; as a consequence the rate of ATP hydrolysis was increased.

Adenosine Diphosphate↗
PubMed1994

Indomethacin inhibition of hog gastric H+/K(+)-ATPase arises from its effect on both the enzyme protein and the lipid bilayer.

Indomethacin showed a dose-, time-, and pH-dependent, noncompetitive inhibitory effect on hog gastric H+/K(+)-ATPase. Four percent of total indomethacin in the buffer (0.20 mmol/liter) bound to the H+/K(+)-ATPase vesicles (15 micrograms/ml). It markedly quenched the intrinsic fluorescence of the enzyme, and decreased the membrane fluidity. Thus, the inhibitor effect of indomethacin may arise from both a direct effect on the hydrolytic and H+ transport functions of the enzyme and a disturbing effect on the lipid bilayer of the vesicle.

Adenosine Triphosphatases↗
PubMed1994

[Soft tissue changes after advancement genioplasty in Chinese adults].

Twenty-five Chinese patients who had undergone advancement genioplasty were evaluated for soft tissue changes of chin. The effects of bony genioplastic advancement on soft tissues of profile were studied by means of computerized cephalometric analysis. The change ratios between soft tissue and hard tissue, as well as regression equations were calculated. The result of this study led to the following conclusions: The soft tissue chin point and labiomental sulcus moved by 85% and 41% of horizontal advancement of the mandibular symphsis.

Adolescent↗
PubMed1994

[Effect of indomethacin on H+ transportation of pig gastric H+/K(+)-ATPase].

As a noncompetitive inhibitor of pig gastric H+/K(+)-ATPase, indomethacin inhibited the H+ transportation function of the enzyme, leading to not only the obvious dissipation of H+/K(+)-ATPase-generated H+ gradients, but also the decreasing of the H+ gradient formation ability of the enzyme. 4% of indomethacin was able to penetrate into the lipid bilayer of H+/K(+)-ATPase vesicles at 0.15 mg/ml protein concentration, which showed an influence of indomethacin to the membrane. Indomethacin reduced the membrane fluidity of H+/K(+)-ATPase vesicles significantly. It also damaged the conformation of membrane protein extraordinarily, which was evidenced by decreasing the intrinsic fluorescence of H+/K(+)-ATPase. From the results, we suggest that the effect of indomethacin on H+/K(+)-ATPase is taken place by its inhibition on H+/K(+)-ATPase protein, as well as by its influence on the membrane lipid bilayer of H+/K(+)-ATPase vesicles.

Animals↗
PubMed1992

Mycobacteria and human heat shock protein-specific cytotoxic T lymphocytes in rheumatoid synovial inflammation.

OBJECTIVE: To study the cytotoxic capacity of mycobacteria-specific T lymphocyte lines and clones from sites of inflammation in patients with rheumatoid arthritis (RA). We also studied antigen specificity, surface phenotype, expression of T cell receptors (TCR), and HLA restriction. METHODS: Autologous macrophages (M phi) from the synovial membrane (SM), synovial fluid (SF), or peripheral blood (PB) were used as target cells in cytotoxicity assays. RESULTS: All SM and SF cell lines tested thus far have shown specific lysis of the autologous M phi from SM or PB that had been pulsed with BCG (bacillus Calmette-Guerin), but no cytotoxicity when the targets were pulsed with irrelevant antigens such as tetanus toxoid and Chlamydia. Both CD4+ and CD8+ cells were shown to be involved in the specific cytolysis. The majority of the cytotoxic T lymphocyte (CTL) lines were TCR alpha/beta + cells. However, both TCR alpha/beta + and TCR gamma/delta + clones (TCR delta 1+) from one RA patient showed antigen-specific lysis. Antigen-specific recognition by a number of CTL lines and clones generated from SF and SM was restricted by HLA-DR molecules. Two Mycobacterium bovis 65-kd heat shock protein (HSP)-specific TCR alpha/beta + SF T cell clones also lysed M phi that had been pulsed with a recombinant human 65-kd HSP. CONCLUSION: Joint inflammation and destruction might be partly attributable to a cross-reaction of mycobacteria-induced cytotoxic T cells with self HSP.

Antibodies, Monoclonal↗
PubMed1992

Peptide recognition, T cell receptor usage and HLA restriction elements of human heat-shock protein (hsp) 60 and mycobacterial 65-kDa hsp-reactive T cell clones from rheumatoid synovial fluid.

A commonly held postulate regarding the etiology of rheumatoid arthritis (RA) is that of antigenic mimicry. Recent interest has focused on the mycobacterial 65-kDa heat-shock protein (hsp) as a putative causal agent. The 65-kDa hsp has over 40% sequence homology with the human hsp 60, and elevated synovial T cell responses to both antigens have been demonstrated in RA and juvenile rheumatoid arthritis patients. Such T cells should, therefore, be specific for shared epitopes on the two antigens. To investigate this, we screened synovial fluid mononuclear cells from two early RA patients with peptides of the 65-kDa hsp which have the greatest homology with the human hsp 60. We also raised a panel of T cell clones from one of the patients with the 65-kDa hsp. The synovial T cell population from both patients and one of the T cell clones recognized a peptide representing the amino-acid sequence 241-255. This clone also responded to the peptide of the equivalent human sequence, and was restricted by HLA-DQ. A second T cell clone recognized an adjacent epitope (amino acid sequence 251-265) which is also highly homologous with the human sequence, but this clone was restricted by HLA-DR. The clones utilized different V beta gene segments but the same D beta and J beta gene elements, and both exhibited specific cytotoxicity against autologous antigen-pulsed macrophages. Our findings, therefore, do not disagree with the postulate that autoimmune disease could possibly be triggered by bacterial epitopes with homology to self protein. However, it is also noted that there are alternative interpretations of this data.

Adult↗
PubMed1990

Human suppressor T cell clones lack CD28.

Previously we showed that certain T cell lines and clones from a lepromatous leprosy patient displayed a dose-dependent suppression of the proliferation of autologous T cells to Mycobacterium leprae (M. leprae) but not mitogen or an unrelated antigen. The latter cells were also cloned and did not display this suppressive activity, were CD4+ and proliferated vigorously to M. leprae presented by autologous HLA-DR molecules. We shall refer to these cells as T helper (Th) cells. Most of the suppressive T cell clones (Ts) were also CD4+ and also proliferated to M. leprae presented by HLA-DR, but much less strongly than Th cells. In this study we report on our search for (a) the mechanism of this apparently antigen-specific suppression by T cells, and (b) a possible phenotypic difference between Th and Ts clones. The two main conclusions are that Ts clones possess a lytic machinery, but that M. leprae-specific suppression and cytotoxicity can be clearly dissociated, and that the only phenotypic difference between Th and Ts is the presence of the CD28 marker on Th and its absence on Ts clones.

Antigens, CD↗
PubMed1990

Phenotypic and functional characterization of human suppressor T-cell clones: II. Activation by Mycobacterium leprae presented by HLA-DR molecules to alpha beta T-cell receptors.

We have been studying human T-cell clones that suppress anti-mycobacterial T-cell responses but not T-cell responses to an unrelated antigen or mitogen. In the present paper we report our studies on the activation requirements of these suppressor-T-cell clones. The suppressor-T-cell clones could proliferate and produce interferon-gamma upon stimulation with Mycobacterium leprae and other mycobacteria but not with unrelated antigens or autologous T cells. Both suppressor and nonsuppressor clones react to a 36-kDa antigen of M. leprae. Thus far, we have not been able to demonstrate whether they see the same or different epitopes. The antigen-driven proliferation of suppressor-T-cell clones was, however, significantly lower than that observed for T-cell clones that did not mediate suppression. The proliferation of suppressor-T-cell clones to M. leprae antigens could be blocked by monoclonal antibodies to HLA-DR, alpha beta T-cell receptor, interleukin-2 receptor, and, in the case of CD4-positive suppressor-T-cell clones, anti-CD4 monoclonal antibodies. DR restriction of the antigen presentation to these suppressor-T-cell clones was shown in mixing experiments using antigen-presenting cells as mononuclear cells from family members and unrelated individuals. These experiments also indicated that apart from regular DR-restriction a hitherto unknown factor may be required for presentation to or activation of suppressor-T-cell clones that is present in the family members and unrelated individuals with the same ethnic and geographic background but absent in DR/Dw-matched healthy Dutch individuals.

Antibodies, Monoclonal↗
PubMed1990

Subtypes of HLA-A1 defined on the basis of CTL precursor frequencies.

Recently we have shown that limiting dilution analysis can be used to detect cytotoxic T-cell precursor frequencies directed against individual HLA class I antigens. Using the same protocol, we have been able to define two subtypes of HLA-A1, which are indistinguishable by conventional typing sera as well as by cell-mediated lympholysis. One-dimensional isoelectric focusing analysis of the variants did not show any overall charge differences. However, family studies indicated that these HLA-A1 subtypes are genetically determined and can be distinguished on the bases of T-cell precursor frequencies in HLA-A1-negative blood donors.

Binding, Competitive↗
PubMed1990

Survey of trichinosis in breeding and cull swine, using an enzyme-linked immunosorbent assay.

Serum samples obtained from 40,927 swine at various locations in North Carolina between Aug 1, 1987 and July 31, 1988, were tested for antibodies to Trichinella spiralis, using an ELISA based on a larval T spiralis excretory-secretory antigen. In the ELISA, samples were considered to have positive results if the optical density (OD) reading was equal to or 5 times greater than the mean OD value of 4 negative-control sera from trichina-free swine. Of the 40,927 serum samples tested, 154 (0.38%) were positive by ELISA; the rate for breeding swine was 0.35% (105/30,162), and the rate for cull swine was 0.45% (49/10,765). Of the 49 seropositive samples from cull swine, 11 were from out of the state, 22 had no identification, and 16 were known to originate from North Carolina. Seropositivity had a bimodally seasonal distribution, with peaks in March and September. There was no difference between the mean age of seropositive and seronegative swine, but males were at greater risk for seropositivity than were females. Pigs from lots with less than 100 sera tested were at increased risk for seropositivity, as were pigs from the central coastal region of North Carolina.

Animals↗
PubMed1989

Analysis of cytotoxic T cell precursor frequencies directed against individual HLA-A and -B alloantigens.

We describe here a limiting dilution analysis to determine cytotoxic T lymphocyte precursor (CTLp) frequencies against individual HLA-A or -B antigens. This assay is reproducible and showed that the CTLp frequency of an individual remains stable with time. Significant variations in CTLp frequency against the same alloantigen were found in different individuals and even in monozygotic twins, showing that these differences were not (completely) genetically determined. Within an individual, a wide range of CTLp frequencies can be found against different allo-antigens. Serologically cross-reactivity seems not to interfere in this assay. This LDA is a practicable tool for a systematic analysis of CTLp response against selected individual HLA-A or -B antigens and can be used for the selection of HLA mismatched donors for transplantation patients.

Cross Reactions↗
PubMed1989

Retroperitoneal lymphangioma. A case report.

Retroperitoneal cystic lymphangiomas are rare benign tumours. Ultrasonography, computed tomography, lymphography or fine-needle percutaneous aspiration may be used to make the diagnosis pre-operatively. Complete excision of the cyst without rupture is the preferred treatment. However, in complicated cases a conservative surgical approach is mandatory.

Humans↗
PubMed1988

Wounding effects of small fragments of different shapes at different velocities on soft tissues of dogs.

The wounding effects of small fragments of the same weight (0.44 gm) but different shapes and at different impact velocities (708-1,560 m/s) on the soft tissues of the hind legs of 156 dogs were studied. The experiments showed that velocity was the major factor in causing wounds. For fragments of the same shape, the energy transmission, volume of wound cavity, sectional areas at entrance and exit, and amount of tissue that had to be excised increased rapidly with increasing velocity. In particular, as the velocity reached about 1,500 m/s, a shallow and wide wound tract was liable to occur, peripheral tissue lesion was relatively apparent, even extended to the whole leg, and the rate of occurrence of bone fracture was high. The wounding effect of the shape of the fragment closely related to its sectional specific weight (W) and drag coefficient (CD). Given the weight of the projectile and the density and thickness of the tissue, the energy transmission (delta E) was directly proportional to the square of the velocity and to the drag coefficient, and inversely proportional to the sectional specific weight of the fragment. Therefore, under certain conditions, reducing the sectional specific weight often increased the drag coefficient, in favour of causing a wound. In this experiment, the extent of wounds caused by the triangular, the square, and the cylindrical, and the spherical fragments decreased in that order, in agreement with their values of sectional specific weight and drag coefficient.

Animals↗