Biomedical subjects

A Nádas

Publications and source records attributed to A Nádas.

11 recordsLinked to original sources

PubMed2001

Additive effects characterize the interaction of antibodies involved in neutralization of the primary dualtropic human immunodeficiency virus type 1 isolate 89.6.

Human immunodeficiency virus-type I (HIV-1) infection elicits antibodies (Abs) directed against several regions of the gp120 and gp41 envelope glycoproteins. Many of these Abs are able to neutralize T-cell-line-adapted strains (TCLA) of HIV-1, but only a few effectively neutralize primary HIV-1 isolates. The nature of HIV-1 neutralization has been carefully studied using human monoclonal Abs (MAbs), and the ability of such MAbs to act in synergy to neutralize HIV-1 has also been extensively studied. However, most synergy studies have been conducted using TCLA strains. To determine the nature of Ab interaction in HIV-1 primary isolate neutralization, a panel of 12 anti-HIV-1 human immunoglobulin G (IgG) MAbs, specific for epitopes in gp120 and gp41, were used. Initial tests showed that six of these MAbs, as well as sCD4, used individually, were able to neutralize the dualtropic primary isolate HIV-1(89.6); MAbs giving significant neutralization at 2 to 10 microg/ml included 2F5 (anti-gp41), 50-69 (anti-gp41), IgG1b12 (anti-gp120(CD4bd)), 447-52D (anti-gp120(V3)), 2G12 (anti-gp120), and 670-D (anti-gp120(C5)). For studies of reagent interaction, 16 binary combinations of reagents were tested for their ability to neutralize HIV-1(89.6). Reagent combinations tested included one neutralizing MAb with sCD4, six pairs consisting of two neutralizing MAbs, and nine pairs consisting of one neutralizing MAb with another non-neutralizing MAb. To assess the interaction of the latter type of combination, a new mathematical treatment of reagent interaction was developed since previously used methods could be used only when both reagents neutralize. Synergy was noted between sCD4 and a neutralizing anti-gp120(V3) MAb. Antagonism was noted between two pairs of anti-gp41 MAbs (one neutralizing and one non-neutralizing). All of the other 13 pairs of MAbs tested displayed only additive effects. These studies suggest that Abs rarely act in synergy to neutralize primary isolate HIV-1(89.6); many anti-HIV-1 Abs act additively to mediate this biological function.

Antibody Specificity↗

PubMed2000

Conserved and exposed epitopes on intact, native, primary human immunodeficiency virus type 1 virions of group M.

We have examined the exposure and conservation of antigenic epitopes on the surface envelope glycoproteins (gp120 and gp41) of 26 intact, native, primary human immunodeficiency virus type 1 (HIV-1) group M virions of clades A to H. For this, 47 monoclonal antibodies (MAbs) derived from HIV-1-infected patients were used which were directed at epitopes of gp120 (specifically V2, C2, V3, the CD4-binding domain [CD4bd], and C5) and epitopes of gp41 (clusters I and II). Of the five regions within gp120 examined, MAbs bound best to epitopes in the V3 and C5 regions. Only moderate to weak binding was observed by most MAbs to epitopes in the V2, C2, and CD4bd regions. Two anti-gp41 cluster I MAbs targeted to a region near the tip of the hydrophilic immunodominant domain bound strongly to >90% of isolates tested. On the other hand, binding of anti-gp41 cluster II MAbs was poor to moderate at best. Binding was dependent on conformational as well as linear structures on the envelope proteins of the virions. Further studies of neutralization demonstrated that MAbs that bound to virions did not always neutralize but all MAbs that neutralized bound to the homologous virus. This study demonstrates that epitopes in the V3 and C5 regions of gp120 and in the cluster I region of gp41 are well exposed on the surface of intact, native, primary HIV-1 isolates and that cross-reactive epitopes in these regions are shared by many viruses from clades A to H. However, only a limited number of MAbs to these epitopes on the surface of HIV-1 isolates can neutralize primary isolates.

Amino Acid Sequence↗

PubMed2000

Immunoreactivity of intact virions of human immunodeficiency virus type 1 (HIV-1) reveals the existence of fewer HIV-1 immunotypes than genotypes.

In order to protect against organisms that exhibit significant genetic variation, polyvalent vaccines are needed. Given the extreme variability of human immunodeficiency virus type 1 (HIV-1), it is probable that a polyvalent vaccine will also be needed for protection from this virus. However, to understand how to construct a polyvalent vaccine, serotypes or immunotypes of HIV must be identified. In the present study, we have examined the immunologic relatedness of intact, native HIV-1 primary isolates of group M, clades A to H, with human monoclonal antibodies (MAbs) directed at epitopes in the V3, C5, and gp41 cluster I regions of the envelope glycoproteins, since these regions are well exposed on the virion surface. Multivariate analysis of the binding data revealed three immunotypes of HIV-1 and five MAb groups useful for immunotyping of the viruses. The analysis revealed that there are fewer immunotypes than genotypes of HIV and that clustering of the isolates did not correlate with either genotypes, coreceptor usage (CCR5 and CXCR4), or geographic origin of the isolates. Further analysis revealed distinct MAb groups that bound preferentially to HIV-1 isolates belonging to particular immunotypes or that bound to all three immunotypes; this demonstrates that viral immunotypes identified by mathematical analysis are indeed defined by their immunologic characteristics. In summary, these results indicate (i) that HIV-1 immunotypes can be defined, (ii) that constellations of epitopes that are conserved among isolates belonging to each individual HIV-1 immunotype exist and that these distinguish each of the immunotypes, and (iii) that there are also epitopes that are routinely shared by all immunotypes.

Antibodies, Monoclonal↗

PubMed2000

Association of particulate matter components with daily mortality and morbidity in urban populations.

Indices of atmospheric particulate matter (PM) have been reported to be associated with daily mortality and morbidity in a large number of recent time-series studies. However, the question remains as to which components of PM are responsible for the reported associations. Multiple PM components rarely are measured simultaneously. To investigate PM effects on mortality and morbidity, we used the multiple PM components measured in Windsor, Ontario, at a site only a few miles from downtown Detroit, Michigan. This study focused primarily on two study periods in which multiple PM components were measured in Windsor: 1985 to 1990, when levels of total suspended particles (TSP), sulfate from TSP (TSP-SO4(2-)), PM less than 10 microns in diameter (PM10), and nonthoracic TSP (TSP-PM10) were measured throughout the year; and 1992 to 1994, when data on PM10, PM2.5 (PM less than 2.5 microns in diameter), PM10-2.5 (PM10 minus PM2.5), particle acidity (H+), and artifact-free sulfates (SO4(2-)) were available for mostly summer months. Mortality data were analyzed for the 1985 to 1990 study period, and data on both mortality and hospital admissions of elderly patients were analyzed for the 1992 through 1994 period. Poisson regressions were used to estimate the effects of these PM components and gaseous criteria pollutants on mortality (nonaccidental, circulatory, respiratory, and nonaccidental without circulatory and respiratory) and on hospital admissions of elderly patients (for pneumonia, chronic obstructive pulmonary disease [COPD], ischemic heart disease, dysrhythmias, heart failure, and stroke), adjusting for temperature and humidity, trends and seasonal cycles, and day of the week. Both PM10 and TSP were associated significantly with respiratory mortality for the 1985 to 1990 period, with similar relative risk (RR) estimates for PM10 (RR = 1.123; 95% confidence interval [CI] 1.0361-1.218) and TSP (RR = 1.109; 95% CI 1.028-1.197), per 5th to 95th percentile increment. The effect-size estimates for TSP-SO4(2-) and TSP-PM10 were smaller and less significant. In two-pollutant models, simultaneous inclusion of gaseous pollutants with PM10 or TSP reduced PM coefficients by 0 to 34%. The effect-size estimates for total mortality, circulatory mortality, and total minus circulatory and respiratory mortality were less than those for respiratory mortality. Ozone (O3) and nitrogen dioxide (NO2) also were associated significantly with total and circulatory mortality, but a simultaneous consideration of these pollutants with PM10 reduced PM10 coefficients only slightly, or even increased them. In these results, pollution coefficients often were positive at multiple lag days (0-day through 3-day lags were examined), but for PM indices, 1-day lag coefficients were most significant. However, when all combinations of multiple-day average exposures were examined, for cases in which multiple lag days were positive, the choice of single-day or multiple-day average exposure did not appreciably change the estimated effect sizes. An examination of temporal correlation showed that the order of spatial uniformity as expressed by the median site-to-site correlation was O3 (0.83), PM10 (0.78), TSP (0.71), NO2 (0.70), carbon monoxide (CO) (0.50), and sulfur dioxide (SO2) (0.49), which suggests less exposure error for O3 and PM10 than for the other measured pollutants. Thus, these results suggest that spatially homogeneous pollution indices show higher associations with measured health outcomes.

Air Pollutants↗

PubMed1999

Immunotyping of human immunodeficiency virus type 1 (HIV): an approach to immunologic classification of HIV.

Because immunologic classification of human immunodeficiency virus type 1 (HIV) might be more relevant than genotypic classification for designing polyvalent vaccines, studies were undertaken to determine whether immunologically defined groups of HIV ("immunotypes") could be identified. For these experiments, the V3 region of the 120-kDa envelope glycoprotein (gp120) was chosen for study. Although antibodies (Abs) to V3 may not play a major protective role in preventing HIV infection, identification of a limited number of immunologically defined structures in this extremely variable region would set a precedent supporting the hypothesis that, despite its diversity, the HIV family, like the V3 region, might be divisible into immunotypes. Consequently, the immunochemical reactivities of 1,176 combinations of human anti-V3 monoclonal Abs (MAbs) and V3 peptides, derived from viruses of several clades, were studied. Extensive cross-clade reactivity was observed. The patterns of reactivities of 21 MAbs with 50 peptides from clades A through H were then analyzed by a multivariate statistical technique. To test the validity of the mathematical approach, a cluster analysis of the 21 MAbs was performed. Five groups were identified, and these MAb clusters corresponded to classifications of these same MAbs based on the epitopes which they recognize. The concordance between the MAb clusters identified by mathematical analysis and by their specificities supports the validity of the mathematical approach. Therefore, the same mathematical technique was used to identify clusters within the 50 peptides. Seven groups of peptides, each containing peptides from more than one clade, were defined. Inspection of the amino acid sequences of the peptides in each of the mathematically defined peptide clusters revealed unique "signature sequences" that suggest structural motifs characteristic of each V3-based immunotype. The results suggest that cluster analysis of immunologic data can define immunotypes of HIV. These immunotypes are distinct from genotypic classifications. The methods described pave the way for identification of immunotypes defined by immunochemical and neutralization data generated with anti-HIV Env MAbs and intact, viable HIV virions.

Antibodies, Monoclonal↗

PubMed1997

Chinese hamster cells expressing antisense to metallothionein become spontaneous mutators.

The functions of metallothioneins (MTs) have been debated for at least a decade. Because it seems unlikely that they evolved only to protect cells against exogenous heavy metals, it has been suggested that MTs have roles in scavenging reactive intermediates, controlling zinc and copper homeostasis, and controlling transfer of zinc to transcription factors and other proteins. Previously, we demonstrated that Chinese hamster G12 cells which overexpress MT have greatly reduced spontaneous mutation rates, suggesting that MT evolved to prevent spontaneous mutagenesis induced by free nuclear zinc ions. We have now isolated G12 transfectants which express antisense RNA to MT. Immunofluorescent staining reveals MT protein in both the nucleus and the cytoplasm in parental cells. A clone expressing high levels of antisense RNA (AMT30) shows reduced basal and induced levels of MT protein. AMT30 cells are hypersensitive to cadmium, zinc, copper and mercury chlorides as well as to menadione. Glutathione levels in AMT30 and G12 cells do not differ. AMT30 cells are spontaneous mutators, showing a spontaneous mutation rate 5-10 times that of G12 cells or G12 cells transfected with vector alone. Only transfectants which show a high level of MT antisense expression (i.e., AMT30) had greatly elevated spontaneous mutation rates. These results support our hypothesis that a major role of MT is to act as an endogenous antimutagen probably via scavenging of reactive intermediates in the nucleus. AMT30 cells should be useful in delineating the sources of spontaneous mutagenesis.

Animals↗

PubMed1996

Maximum likelihood estimation of spontaneous mutation rates from large initial populations.

When estimating a spontaneous mutation rate from either a single culture (C=1) or from the C parallel cultures (C>1) of a fluctuation experiment, the use of a large initial population size N0 to seed each culture will permit a gaussian approximation for the probability distribution of the number M of mutants at the time when the culture(s) has (have) grown to size N=N02g, i.e., experienced g doublings. Using this gaussian approximation we find that the maximum likelihood estimate mu of the expected number mu of mutants present in a culture in generation g is (exactly) (equation: see text) where r = 2g / g and M 2 is the average of the squares of the C mutant counts. The maximum likelihood estimate p of the unknown mutation rate p is p = 2 mu / gN assuming an 'ideal' experiment and that there were no mutants in the initial population. A well-behaved maximum likelihood estimate is known to be efficient in large samples and we illustrate by Monte Carlo simulation that indeed p is better (has smaller mean squared error) than our previous (Rossman et al., 1995) estimator (equation: see text) (M is the average mutant count) provided N0 is of the order 1/p or larger. This advantage exists even without a fluctuation experiment, i.e., for C = 1.

Animals↗

PubMed1996

Serum deprivation, but not inhibition of growth per se, induces a hypermutable state in Chinese hamster G12 cells.

Spontaneous mutagenesis is thought to play a crucial role in spontaneous carcinogenesis. We recently described a new mathematical model for estimation of the spontaneous mutation rate (mutation/gene/generations) based on the assumption that mutations are fixed in the S-phase of the cell cycle. With this definition, the spontaneous mutation rate should be independent of the growth rate. In the present study, we tested this hypothesis, using cell line G12, a transgenic Chinese hamster V79 derivative, which contains a single copy of the Escherichia coli gpt gene as a target for mutagenesis. The growth rate was modulated by varying the serum concentration or the seeding density, or by addition of suramin, transforming growth factor beta, or dichlorobenzimidazole riboside to the medium. Significant increases in the spontaneous mutation rate occurred when cell proliferation was blocked by serum deprivation. Density-dependent inhibition of growth and inhibition of growth by suramin, transforming growth factor beta, or dichlorobenzimidazole riboside did not result in significant increases in spontaneous mutation rates. The level of oxidants in cells cultivated in the presence of low concentrations of serum was higher compared to control cells, suggesting that the increases in the spontaneous mutation rates under low serum conditions may be partly a result of oxidative stress due to a lack of serum antioxidants. This was shown to be the case, because spontaneous mutation rates were significantly reduced in serum-depleted cells when antioxidants were added to the medium. We suggest that during carcinogenesis, when tumors are in a prevascularized state, the spontaneous mutation rate may be elevated, and this process may contribute to the genetic instability of the tumor cells.

Animals↗

PubMed1996

Mutations and infinity: improved statistical methods for estimating spontaneous rates.

Certain mathematical artifacts which had been appended by others to Luria and Delbrück's [Genetics 28: 491-511, 1943] model of spontaneous mutagenesis in bacterial populations have added confusion to the modeling and measurement of spontaneous mutation rates. Additional confusion arises when models which had been tuned for experiments with bacterial cultures grown from a small inoculum are adapted for use with mammalian cell cultures grown from a large initial population. As one consequence, biologists still tend to grow the large number of parallel cultures required by the fluctuation test in order to avoid large errors due to the high variability in the number of mutants in a growing culture. By avoiding models with infinite mean values and certain mathematical approximations that lead to conceptual and practical difficulties, the large variance of the number of mutants can be avoided (and the precision of the estimated mutation rate controlled) through the use of sufficiently large initial cell populations. A direct consequence is that simpler experiments with fewer cultures may suffice. In this paper, after a discussion of the confusions, we extend our previous approach [Rossman et al.: Mutat Res 328:21-30, 1995] by giving improved formulas for the standard error of the estimated mutation rate. The improvement results from using a more inclusive model based on consideration of the variability due to both the biological phenomenon of the growing culture (growth and mutation) and the protocols used for selection (sampling and plating efficiency). Also included is the situation where the initial cell population is not assumed to be free of mutants but the initial mutant fraction is measured instead. These standard error formulas are useful in planning experiments that yield mutation rate estimates with planned precision and for comparing and testing hypotheses about mutation rates in two or more populations which are grown under different conditions.

Cell Culture Techniques↗

PubMed1995

Modeling and measurement of the spontaneous mutation rate in mammalian cells.

The study of spontaneous mutation rates in mammalian cells has been hampered by the lack of an alternative to the cumbersome Luria and Delbrück fluctuation test. A brief review of mathematical treatments of spontaneous mutagenesis, along with some of the limitations of the fluctuation test, is presented. A new experimental method and a simple mathematical model for deriving the spontaneous mutation rate are described. Data from the transgenic Chinese hamster G12 cell line growing at two different rates is analyzed according to this model. The results support the concept that, at least for growing cells, the spontaneous mutation rate is independent of the growth rate, and the mutant fraction increases in a linear fashion with the number of generations.

Animals↗

PubMedDate not supplied

Monitor-to-monitor temporal correlation of air pollution and weather variables in the North-Central U.S.

Numerous time series studies have reported associations between daily ambient concentrations of air pollution and morbidity or mortality. Recent personal exposure studies have also reported relatively high longitudinal correlation between personal exposures to particulate matter (PM) and home outdoor PM concentrations, lending support to the health effects reported in time series studies. However, the question remains as to how well the temporal fluctuations in the air pollution levels observed at an outdoor monitor represent the temporal fluctuations in the population exposures to pollution of outdoor origins in a city, and how such representativeness affects the size and significance of risk estimates. Also, such spatio-temporal correlations would vary from pollutant to pollutant, likely influencing their relative significance of statistical associations with health outcomes. In this study, we characterized the extent of monitor-to-monitor correlation over time among multiple monitoring sites for PM less than 10 microm (PM10), gaseous criteria pollutants, and several weather variables in seven central and eastern contiguous states (IL, IN, MI, OH, PA, WI, and WV) during the study period of 1988-1990. After removing seasonal trends, the monitor-to-monitor temporal correlation among the air pollution/weather variables within 100-mile separation distance in these areas could be generally ranked into three groups: (1 ) temperature, dew point, relative humidity (r>0.9); (2) O3, PM10, NO2 (r: 0.8-0.6); and (3) CO, SO2 (r<0.5). Using the subsets for separation distance less than 100 miles, regression analyses of these monitor-to-monitor correlation coefficients were also conducted with explanatory variables including separation distance, qualitative (land use, location setting, and monitoring objectives) and quantitative (large and small variance) site characteristics, and region indicators for Air Quality Control Region (AQCR). The separation distance was a significant predictor of monitorto-monitor correlation decline especially for PM10 and NO2 (approximately 0.2 drop over 30 miles). Site characteristic variables were, in some cases, significant predictors of monitor-to-monitor correlation, but the magnitude of their impacts was not substantial. Regional differences, as examined by AQCR, were in some cases (e.g., in Metropolitan Philadelphia) substantial. In these areas, the pollutants that had generally poor monitor-to-monitor correlation in the overall seven states data (i.e., for SO2 and CO) showed higher monitor-to-monitor correlations, comparable with PM10 and O3, within the AQCR. These results are useful in interpreting some of the past time series epidemiological results. The differences in monitor-to-monitor correlations found across pollutants in this work (i.e., r approximately 0.8 vs. r approximately 0.4) are sufficiently large that they could be a factor in the different pollutant significance levels reported in the epidemiologic literature. It is recommended that future epidemiological studies collect and incorporate information on spatial variability among air pollutants in the analysis and interpretation of their results.

Air Pollution↗