Genomic Surveillance for SARS-CoV-2 Variants: Circulation of Omicron Lineages - United States, January 2022-May 2023

CDC has used national genomic surveillance since December 2020 to monitor SARS-CoV-2 variants that have emerged throughout the COVID-19 pandemic, including the Omicron variant. This report summarizes U.S. trends in variant proportions from national genomic surveillance during January 2022-May 2023. During this period, the Omicron variant remained predominant, with various descendant lineages reaching national predominance (>50% prevalence). During the first half of 2022, BA.1.1 reached predominance by the week ending January 8, 2022, followed by BA.2 (March 26), BA.2.12.1 (May 14), and BA.5 (July 2); the predominance of each variant coincided with surges in COVID-19 cases. The latter half of 2022 was characterized by the circulation of sublineages of BA.2, BA.4, and BA.5 (e.g., BQ.1 and BQ.1.1), some of which independently acquired similar spike protein substitutions associated with immune evasion. By the end of January 2023, XBB.1.5 became predominant. As of May 13, 2023, the most common circulating lineages were XBB.1.5 (61.5%), XBB.1.9.1 (10.0%), and XBB.1.16 (9.4%); XBB.1.16 and XBB.1.16.1 (2.4%), containing the K478R substitution, and XBB.2.3 (3.2%), containing the P521S substitution, had the fastest doubling times at that point. Analytic methods for estimating variant proportions have been updated as the availability of sequencing specimens has declined. The continued evolution of Omicron lineages highlights the importance of genomic surveillance to monitor emerging variants and help guide vaccine development and use of therapeutics.

Informing Building Strategies to Reduce Infectious Aerosol Transmission Risk by Integrating DNA Aerosol Tracers with Quantitative Microbial Risk Assessment

Using aerosol-based tracers to estimate risk of infectious aerosol transmission aids in the design of buildings with adequate protection against aerosol transmissible pathogens, such as SARS-CoV-2 and influenza. We propose a method for scaling a SARS-CoV-2 bulk aerosol quantitative microbial risk assessment (QMRA) model for impulse emissions, coughing or sneezing, with aerosolized synthetic DNA tracer concentration measurements. With point-of-emission ratios describing relationships between tracer and respiratory aerosol emission characteristics (i.e., volume and RNA or DNA concentrations) and accounting for aerosolized pathogen loss of infectivity over time, we scale the inhaled pathogen dose and risk of infection with time-integrated tracer concentrations measured with a filter sampler. This tracer-scaled QMRA model is evaluated through scenario testing, comparing the impact of ventilation, occupancy, masking, and layering interventions on infection risk. We apply the tracer-scaled QMRA model to measurement data from an ambulatory care room to estimate the risk reduction resulting from HEPA air cleaner operation. Using DNA tracer measurements to scale a bulk aerosol QMRA model is a relatively simple method of estimating risk in buildings and can be applied to understand the impact of risk mitigation efforts.

SARS-CoV-2 Delta-Omicron Recombinant Viruses, United States

To detect new and changing SARS-CoV-2 variants, we investigated candidate Delta-Omicron recombinant genomes from Centers for Disease Control and Prevention national genomic surveillance. Laboratory and bioinformatic investigations identified and validated 9 genetically related SARS-CoV-2 viruses with a hybrid Delta-Omicron spike protein.

A case report of Salmonella enterica serovar Corvallis from environmental isolates from Cambodia and clinical isolates in the UK

Salmonella enterica subspecies enterica serovar Corvallis (S. Corvallis) has been identified as a human pathogen and as a food contaminant. Diarrhoeal disease is a common diagnosis in tourists visiting Southeast Asia, often with unknown aetiology. However, numerous public health institutes have identified Salmonella as a common causative agent when consuming contaminated food and water. Genomic data from environmental isolates from a Cambodian informal market were uploaded to the National Center for Biotechnology Information (NCBI) platform, allowing the novel sequences to be compared to global whole-genome sequence archives. The comparison revealed that two human clinical isolates from England and four of the environmental isolates were closely related, with an average single nucleotide polymorphism (SNP) difference of 1 (0-3 SNPs). A maximum-likelihood tree based on core SNPs was generated comparing the 4 isolates recovered from a Cambodian informal market with 239 isolates of S. Corvallis received from routine surveillance of human salmonellosis in England and confirmed the close relationship. In addition, the environmental isolates clustered into a broader phylogenetic group within the S. Corvallis population containing 68 additional human isolates, of which 42 were from patients who reported recent international travel, almost exclusively to Southeast Asia. The environmental isolates of S. Corvallis isolated from an informal market in Cambodia are concerning for public health due to their genetic similarity to isolates (e.g. clinical isolates from the UK) with known human virulence and pathogenicity. This study emphasizes the benefits of global and public data sharing of pathogen genomes.

Genotypic and Phenotypic Characterization of Antimicrobial Resistance Profiles in Non-typhoidal Salmonella enterica Strains Isolated From Cambodian Informal Markets

Non-typhoidal Salmonella enterica is a pathogen of global importance, particularly in low and middle-income countries (LMICs). The presence of antimicrobial resistant (AMR) strains in market environments poses a serious health threat to consumers. In this study we identified and characterized the genotypic and phenotypic AMR profiles of 81 environmental S. enterica strains isolated from samples from informal markets in Cambodia in 2018–2019. AMR genotypes were retrieved from the NCBI Pathogen Detection website (https://www.ncbi.nlm.nih.gov/pathogens/) and using ResFinder (https://cge.cbs.dtu.dk/services/) Salmonella pathogenicity islands (SPIs) were identified with SPIFinder (https://cge.cbs.dtu.dk/services/). Susceptibility testing was performed by broth microdilution according to the Clinical and Laboratory Standards Institute (CLSI) standard guidelines M100-S22 using the National Antimicrobial Resistance Monitoring System (NARMS) Sensititre Gram Negative plate. A total of 17 unique AMR genes were detected in 53% (43/81) of the isolates, including those encoding tetracycline, beta-lactam, sulfonamide, quinolone, aminoglycoside, phenicol, and trimethoprim resistance. A total of 10 SPIs (SPI-1, 3–5, 8, 9, 12–14, and centisome 63 [C63PI]) were detected in 59 isolates. C63PI, an iron transport system in SPI-1, was observed in 56% of the isolates (n = 46). SPI-1, SPI-4, and SPI-9 were present in 13, 2, and 5% of the isolates, respectively. The most common phenotypic resistances were observed to tetracycline (47%; n = 38), ampicillin (37%; n = 30), streptomycin (20%; n = 16), chloramphenicol (17%; n = 14), and trimethoprim-sulfamethoxazole (16%; n = 13). This study contributes to understanding the AMR genes present in S. enterica isolates from informal markets in Cambodia, as well as support domestic epidemiological investigations of multidrug resistance (MDR) profiles.

Early introductions and transmission of SARS-CoV-2 variant B.1.1.7 in the United States

The emergence and spread of SARS-CoV-2 lineage B.1.1.7, first detected in the United Kingdom, has become a global public health concern because of its increased transmissibility. Over 2,500 COVID-19 cases associated with this variant have been detected in the United States (US) since December 2020, but the extent of establishment is relatively unknown. Using travel, genomic, and diagnostic data, we highlight that the primary ports of entry for B.1.1.7 in the US were in New York, California, and Florida. Furthermore, we found evidence for many independent B.1.1.7 establishments starting in early December 2020, followed by interstate spread by the end of the month. Finally, we project that B.1.1.7 will be the dominant lineage in many states by mid- to late March. Thus, genomic surveillance for B.1.1.7 and other variants urgently needs to be enhanced to better inform the public health response.

Early introductions and community transmission of SARS-CoV-2 variant B.1.1.7 in the United States

The emergence and spread of SARS-CoV-2 lineage B.1.1.7, first detected in the United Kingdom, has become a global public health concern because of its increased transmissibility. Over 2500 COVID-19 cases associated with this variant have been detected in the US since December 2020, but the extent of establishment is relatively unknown. Using travel, genomic, and diagnostic data, we highlight the primary ports of entry for B.1.1.7 in the US and locations of possible underreporting of B.1.1.7 cases. Furthermore, we found evidence for many independent B.1.1.7 establishments starting in early December 2020, followed by interstate spread by the end of the month. Finally, we project that B.1.1.7 will be the dominant lineage in many states by mid to late March. Thus, genomic surveillance for B.1.1.7 and other variants urgently needs to be enhanced to better inform the public health response.

A Systematic Approach to Identify and Characterize the Effectiveness and Safety of Novel Probiotic Strains to Control Foodborne Pathogens

A total of 44 lactic acid bacteria (LAB) strains originally isolated from cattle feces and different food sources were screened for their potential probiotic features. The antimicrobial activity of all isolates was tested by well-diffusion assay and competitive exclusion on broth against Salmonella Montevideo, Escherichia coli O157:H7 and Listeria monocytogenes strain N1-002. Thirty-eight LAB strains showed antagonistic effect against at least one of the pathogens tested in this study. Improved inhibitory effect was observed against L. monocytogenes with zones of inhibition up to 24 mm when LAB overnight cultures were used, and up to 21 mm when cell-free filtrates were used. For E. coli O157:H7 and Salmonella maximum inhibitions of 12 and 11.5 mm were observed, respectively. On broth, 43 strains reduced L. monocytogenes up to 9.06 log₁₀ CFU/ml, 41 reduced E. coli O157:H7 up to 0.84 log₁₀ CFU/ml, and 32 reduced Salmonella up to 0.94 log₁₀ CFU/ml 24 h after co-inoculation. Twenty-eight LAB isolates that exhibited the highest inhibitory effect among pathogens were further analyzed to determine their antimicrobial resistance profile, adhesion potential, and cytotoxicity to Caco-2 cells. All LAB strains tested were susceptible to ampicillin, linezolid, and penicillin. Twenty-six were able to adhere to Caco-2 cells, five were classified as highly adhesive with > 40 bacterial cells/Caco-2 cells. Low cytotoxicity percentages were observed for the candidate LAB strains with values ranging from -5 to 8%. Genotypic identification by whole genome sequencing confirmed all as members of the LAB group; Enterococcus was the genus most frequently isolated with 21 isolates, followed by Pediococcus with 4, and Lactobacillus with 3. In this study, a systematic approach was used for the improved identification of novel LAB strains able to exert antagonistic effect against important foodborne pathogens. Our findings suggest that the selected panel of LAB probiotic strains can be used as biocontrol cultures to inhibit and/or reduce the growth of L. monocytogenes, Salmonella, and E. coli O157:H7 in different matrices, and environments.

Survival and internalization of Salmonella and Escherichia coli O157:H7 sprayed onto different cabbage cultivars during cultivation in growth chambers

BACKGROUND

Cabbage may become contaminated with enteric pathogens during cultivation. Using multiple cabbage cultivars at two maturity stages (small plants or plants with small heads) in growth chamber studies, the fate (internalization or surface survival) of Salmonella and Escherichia coli O157:H7 (0157) were examined in conjunction with any potential relationships to the plant's antimicrobial content.

RESULTS

Internalized Salmonella was detected in cabbage within 24 h with prevalence ranging from 62% (16 of 26) for the 'Super Red 80' cultivar to 92% (24 of 26) for the 'Red Dynasty' cultivar. Surface survival of pathogens on small cabbage plants over nine days was significantly affected by cultivar with both pathogens surviving the most on the 'Farao' cultivar and Salmonella and O157 surviving the least on the 'Super Red 80' and 'Capture' cultivars, respectively (P < 0.05). Survival of O157 was slightly higher on cabbage heads for O157 than small plants suggesting that the maturity stage may affect this pathogen's fate. An inverse relationship existed between antimicrobial levels and the pathogen's surface survival on cabbage heads (P < 0.05).

CONCLUSIONS

The fate of pathogens varied with the cabbage cultivar in growth chamber studies highlighting the potential to explore cultivar in field studies to reduce the risk of microbiological contamination in this crop. © 2019 Society of Chemical Industry.

Efficacy of Acetic Acid or Chitosan for Reducing the Prevalence of Salmonella- and Escherichia coli O157:H7-Contaminated Leafy Green Plants in Field Systems

Outbreaks associated with fresh-cut leafy greens continue to occur despite efforts to implement horticultural practices that minimize introduction of enteric pathogens to the crop. The experimental trials in this study were designed to examine the efficacy of an acetic acid (AA)- and chitosan-based spray treatment, applied 1 day prior to harvest, for reducing the prevalence of Escherichia coli O157:H7 (O157) and Salmonella in field-grown leafy greens contaminated at levels detectable only through enrichment culture. Responses to the treatment solution were variable and depended on the type of leafy green (leafy lettuce, spinach, or cabbage), cultivar, pathogen, and AA concentration (0.3 to 0.7%). No significant differences in E. coli O157 prevalence were found for untreated and treated cabbage heads and spinach plants (P > 0.05). In contrast, treatment significantly affected Salmonella on 'Bravo F1' green cabbage and '7-Green' spinach (P < 0.05), with odds ratios of 2.2 and 3.3 for finding the pathogen on untreated versus treated greens, respectively. Salmonella was also 7.1 times more likely to be found on an untreated lettuce plant than on a lettuce plant sprayed with a 0.7% AA treatment solution (95% confidence interval [CI], 4.1 to 12.2; P < 0.0001). In studies addressing the efficacy of chitosan (0.1 or 0.3%), this chemical failed to reduce the prevalence of either pathogen on lettuce (P > 0.05). Similarly, spraying with 0.3% AA did not affect the prevalence of Salmonella on lettuce plants (P > 0.05); however, treatment solutions with 0.4% AA reduced the likelihood of detecting Salmonella in treated versus untreated plants by 6.6 times (95% CI, 2.1 to 20.9; P = 0.0007). After the lettuce was harvested and hand washed, consumers failed to distinguish either visually or organoleptically between untreated lettuce and lettuce sprayed with an acetic acid solution (P > 0.05). These results indicate that acetic acid could be used to reduce the microbiological risk of preharvest leafy greens.

Survival of Salmonella enterica and Escherichia coli O157:H7 Sprayed onto the Foliage of Field-Grown Cabbage Plants

To reduce the number of cabbage pathogen outbreaks, it is essential to understand the fate of enteric pathogens that contaminate plants in the field. To assist in that effort, two independent trials were conducted with a red cultivar (cv. Red Dynasty) and a green cultivar (cv. Bravo F1) of field-grown cabbage ( Brassica oleracea var. capitata). In the first trial, plants with small heads were sprayed with an inoculum containing both attenuated Salmonella enterica Typhimurium and Escherichia coli O157:H7 (5.0 log CFU/mL). Initial pathogen levels (ca. 3.9 log CFU per head), determined through plate count enumeration (limit of detection was 1.3 log CFU/g), dropped precipitously such that 2 days later, they could not be detected by enrichment culture in 22 to 35% of the heads. However, subsequent declines were at a slower rate; no differences were observed between red and green cabbage heads ( P > 0.05), and heads were still positive for the pathogens 22 days after being sprayed with the inoculum. As a result, the logistic model revealed that for every 2 days contaminated cabbage heads remained in the field, the probability of finding a positive sample decreased by a factor of 1.1 (95% confidence interval from 1.0 to 1.2, P = 0.0022) and 1.2 (95% confidence interval from 1.0 to 1.4, P ≤ 0.0001) for Salmonella and E. coli O157:H7, respectively. In the second trial occurring 2 weeks later, plants with medium red or green cabbage heads were sprayed with an inoculum at a dose of 3.5 log CFU/mL. A similar decay in prevalence over time occurred for green cabbage as in trial 1; however, pathogen decline in red cabbage was less in trial 2 than in trial 1. The extended persistence of pathogens in cabbage heads exhibited in both trials infers that harvest of contaminated cabbage destined for raw consumption is risky. Additional field studies are necessary to determine whether similar pathogen fates occur in other regions or climates and to clarify the effect of the maturity of red cabbage on pathogen inactivation.

Pre-harvest internalization and surface survival of Salmonella and Escherichia coli O157:H7 sprayed onto different lettuce cultivars under field and growth chamber conditions

Plant genotype has been advocated to have an important role in the fate of enteric pathogens residing in lettuce foliage. This study was therefore undertaken under the premise that different pathogen responses could occur in lettuce cultivars with cultivar selection being one of several hurdles in an overall strategy for controlling foodborne pathogens on field-grown produce. Up to eight lettuce cultivars ('Gabriella', 'Green Star', 'Muir', 'New Red Fire', 'Coastal Star', 'Starfighter', 'Tropicana', and 'Two Star') were examined in these experiments in which the plants were subjected to spray contamination of their foliage with pathogens. In an experiment that addressed internalization of Salmonella, cultivar was determined to be a significant variable (P < 0.05) with 'Gabriella' and 'Muir' being the least and most likely to exhibit internalization of this pathogen, respectively. Furthermore, antimicrobials (total phenols and antioxidant capacity chemicals) could be part of the plant's defenses to resist internalization as there was an inverse relationship between the prevalence of internalization at 1 h and the levels of these antimicrobials (r = -0.75 to -0.80, P = 0.0312 to 0.0165). Internalized cells appeared to be transient residents in that across all cultivars, plants sampled 1 h after being sprayed were 3.5 times more likely to be positive for Salmonella than plants analyzed 24 h after spraying (95% CI from 1.5 to 8.2, P = 0.0035). The fate of surface-resident Salmonella and Escherichia coli O157:H7 was addressed in subsequent growth chamber and field experiments. In the growth chamber study, no effect of cultivar was manifested on the fate of either pathogen when plants were sampled up to 12 days after spray contamination of their foliage. However, in the field study, five days after spraying the plants, Salmonella contamination was significantly affected by cultivar (P < 0.05) and the following order of prevalence of contamination was observed: 'Muir' < 'Gabriella' < 'Green Star' = 'New Red Fire' < 'Coastal Star'. Nine days after spray contamination of plants in the field, no effect of cultivar was exhibited due primarily to the low prevalence of contamination observed for Salmonella (8 of 300 plant samples positive by enrichment culture) and E. coli O157 (4 of 300 plant samples positive by enrichment culture). Given the narrow window of time during which cultivar differences were documented, it is unlikely that cultivar selection could serve as a viable option for reducing the microbiological risk associated with lettuce.

Characterization of Antimicrobial Resistant (AMR) Salmonella Enterica Isolates Associated With Cattle at Harvest in Mexico

Despite being the target of control efforts for many decades, Salmonella enterica continues to be linked with a large amount of foodborne illnesses and outbreaks worldwide. Over the years, Salmonella isolated from meat products have exhibited a high level of antibiotic resistance. In this study, a total of 351 Salmonella isolates, recovered from cattle fecal samples (n = 31), hides (n = 105), and beef carcasses (n = 215) from 3 abattoirs in Mexico were analyzed for antimicrobial susceptibility. Resistance to at least one antimicrobial drug was found in 205 (58.4%) isolates and 20 different resistance phenotypes were observed among this Salmonella isolates set. Resistance to tetracycline (40.2%) and nalidixic acid (21.1%) was most commonly observed. Additionally, the most common multidrug-resistant (MDR) phenotypes shared resistance to chloramphenicol, streptomycin, tetracycline, and trimethopin/sulfamethoxazole (11.3%), resistance to ampicillin, tetracycline, and trimethopin/sulfamethoxazole (3.4%), and resistance to ampicillin, streptomycin, and tetracycline (2.5%). When it came to antimicrobial resistance phenotypes in each abattoir, we determined there was no statistical difference in the frequency of resistant vs. susceptible Salmonella isolates among the three abattoirs (P > 0.05). These data indicate that Salmonella isolates recovered from beef cattle in Mexico are commonly resistant to antimicrobials and often multiple antimicrobials. In Mexico, antimicrobial resistance, and in particular, multidrug-resistance, maybe of particular concern due to the much higher prevalence of Salmonella in retail beef. This may lead to the spread of resistance and to the reduction of antibiotic efficacy for the control of animal and human infections. Promoting control measures and inspection standards on imported animals and food products should be applied to avoid the spread of antibiotic resistance in various populations and among countries.

Disposition of Salmonella and Escherichia coli O157:H7 following Spraying of Contaminated Water on Cucumber Fruit and Flowers in the Field

Cucumbers are frequently consumed raw and have been implicated in several recent foodborne outbreaks. Because this item may become contaminated at the farm, it is vital to explore the fate of attenuated Salmonella Typhimurium or Escherichia coli O157:H7 sprayed onto foliage, flowers, and fruit in fields and determine whether pre- or postcontamination spray interventions could minimize contamination. After spraying cucumber plants with contaminated irrigation water (3.8 log CFU/mL of Salmonella Typhimurium and E. coli O157:H7), 60 to 78% of cucumber fruit were not contaminated because the plant's canopy likely prevented many of the underlying fruit from being exposed to the water. Subsequent exposure of contaminated cucumber plants to a simulated shower event did not appear to dislodge pathogens from contaminated foliage onto the fruit, nor did it appear to consistently wash either pathogen from the fruit. Spraying flowers and attached ovaries directly with a pathogen inoculum (4.6 log CFU/mL) initially led to 100% and 65 to 90% contamination, respectively. Within 3 days, 30 to 40% of the flowers were still contaminated; however, contamination of ovaries was minimal (≤10%), suggesting it was unlikely that internalization occurred through the flower to the ovary with these pathogen strains. In another study, both pathogens were found on a withered flower but not on the fruit to which the flower was attached, suggesting that this contaminated flower could serve as a source of cross-contamination in a storage bin if harvested with the fruit. Because pre- and postcontamination acetic acid-based spray treatments failed to reduce pathogen prevalence, the probability that fruit initially contaminated at 1.3 to 2.8 log CFU of Salmonella Typhimurium or E. coli O157:H7 per cucumber would be positive by enrichment culture decreased by a factor of 1.6 and 1.9 for Salmonella Typhimurium and E. coli O157:H7, respectively, for every day the fruit was held in the field ( P ≤ 0.0001). Hence, to reduce the prevalence of Salmonella Typhimurium on cucumbers below 5%, more than 1 week would be required.

The prevalence of Escherichia coli O157:H7 fecal shedding in feedlot pens is affected by the water-to-cattle ratio: A randomized controlled trial

Escherichia coli O157:H7 fecal shedding in feedlot cattle is common and is a public health concern due to the risk of foodborne transmission that can result in severe, or even fatal, disease in people. Despite a large body of research, few practical and cost-effective farm-level interventions have been identified. In this study, a randomized controlled trial was conducted to assess the effect of reducing the level of water in automatically refilling water-troughs on fecal shedding of E. coli O157:H7 in feedlot cattle. Pens in a feedlot in the Texas Panhandle were randomly allocated as control (total number: 17) or intervention (total number: 18) pens. Fecal samples (2,759 in total) were collected both at baseline and three weeks after the intervention, and tested for the presence of E. coli O157:H7 using immunomagnetic bead separation and selective culture. There was a strong statistical association between sampling date and the likelihood of a fecal sample testing positive for E. coli O157:H7. Pen was also a strong predictor of fecal prevalence. Despite accounting for this high level of clustering, a statistically significant association between reduced water levels in the trough and increased prevalence of E. coli O157:H7 in the feces was observed (Odds Ratio = 1.6; 95% Confidence Interval: 1.2–2.0; Likelihood Ratio Test: p = 0.02). This is the first time that such an association has been reported, and suggests that increasing water-trough levels may be effective in reducing shedding of E. coli O157:H7 in cattle feces, although further work would be needed to test this hypothesis. Controlling E. coli O157:H7 fecal shedding at the pre-harvest level may lead to a reduced burden of human foodborne illness attributed to this pathogen in beef.

Enhanced Sanitation Standard Operating Procedures Have Limited Impact on Listeria monocytogenes Prevalence in Retail Delis

In a recent longitudinal surveillance study in 30 U.S. retail delicatessens, 9.7% of environmental surfaces were positive for Listeria monocytogenes, and we found substantial evidence of persistence. In this study, we aimed to reduce the prevalence and persistence of L. monocytogenes in the retail deli environment by developing and implementing practical and feasible intervention strategies (i.e., sanitation standard operating procedures; SSOPs). These SSOPs were standardized across the 30 delis enrolled in this study. SSOP implementation was verified by systems inherent to each retailer. Each deli also was equipped with ATP monitoring systems to verify effective sanitation. We evaluated intervention strategy efficacy by testing 28 food and nonfood contact surfaces for L. monocytogenes for 6 months in all 30 retail delis. The efficacy of the intervention on the delis compared with preintervention prevalence level was not statistically significant; we found that L. monocytogenes could persist despite implementation of enhanced SSOPs. Systematic and accurate use of ATP monitoring systems varied widely among delis. The findings indicate that intervention strategies in the form of enhanced daily SSOPs were not sufficient to eliminate L. monocytogenes from highly prevalent and persistently contaminated delis and that more aggressive strategies (e.g., deep cleaning or capital investment in redesign or equipment) may be necessary to fully mitigate persistent contamination.

Adenosine- and adenine-nucleotide-mediated inhibition of normal and transformed keratinocyte proliferation is dependent upon dipyridamole-sensitive adenosine transport

Extracellular adenosine and its related nucleotides have been referred to as retaliatory metabolites that can be released into the extracellular environment during inflammation, wounding, and other pathologic states. We have previously reported that these compounds reversibly inhibit the proliferation of normal keratinocyte cultures and we now demonstrate that these compounds also arrest the proliferation of transformed keratinocytes. Although our study shows that keratinocytes express mRNA corresponding to the A2B purinoreceptors and that adenosine or AMP treatment elevates intracellular cAMP in these cells, our study also demonstrates that dipyridamole-inhibitable transport of adenosine into the keratinocyte is central to the mechanism by which adenosine and adenine nucleotides arrest proliferation in these cells. In support of this mechanism, our results demonstrate that human keratinocytes express mRNA corresponding to the recently cloned dipyridamole-sensitive human equilibrative nucleoside transporter. Interestingly, coincubation with adenosine deaminase reverses the antiproliferative action of adenosine and exerts no effect on the antiproliferative activity of the adenine nucleotides, thus supporting a model in which adenine nucleotides are enzymatically converted to adenosine and transported into the keratinocyte in a tightly coupled and adenosine-deaminase-resistant manner. Analysis of adenosine- and adenosine-monophosphate-treated keratinocytes demonstrated that quiescence is induced within 12-24 h, and fluorescence-activated cell sorter analysis suggests that treatment with these compounds may result in the inhibition of keratinocyte proliferation at both G1 and S phases of the cell cycle. In addition to their documented antiproliferative action on other cell types, adenosine, adenine nucleotides, and related analogs may also represent a potential new class of pharmacologic regulators of keratinocyte proliferation in vivo.

Autocrine regulation of keratinocytes: the emerging role of heparin-binding, epidermal growth factor-related growth factors

Although originally conceived as a basis for malignant cell growth, autocrine signaling networks are currently known to be activated during tissue repair and with in vitro cultivation. In human epidermal keratinocytes, activation of the epidermal growth factor receptor by cognate ligands mediates the majority of the autonomous replicative capacity of these cells and is necessary to inhibit differentiation and apoptosis. The importance of heparin-binding growth factors in activation of this receptor was first suggested by the strong anti-proliferative effects of soluble heparin-like molecules on keratinocyte growth. This and related evidence led to the identification of amphiregulin as a major autocrine factor for keratinocytes. The binding of amphiregulin and its homolog, heparin-binding epidermal growth factor-like growth factor, to the receptor is potentially amplified by autoinduction and cross-signaling through epidermal growth factor-related polypeptides and by transmodulation of other ErbB-family receptors (HER-2, -3, -4) in cells expressing these receptors. Heparan sulfate proteoglycans and the tetraspanin family of membrane-associated proteins appear to act as cofactors in amphiregulin-driven mitogenesis mediated by the epidermal growth factor receptor, but amphiregulin's immunolocalization to keratinocyte nuclei and to filopodia may indicate other potentially novel effects. Following from the observation that amphiregulin is overexpressed in lesional psoriatic epidermis, the importance of amphiregulin in hyperproliferative skin diseases has been further supported by recent studies of the targeted expression of a transgene encoding keratin 14 promoter-driven human amphiregulin to the basal epidermis of mice. Founder transgenic mice displayed a morphologic and microscopic cutaneous phenotype that shares characteristics with psoriasis. Pharmacologic regulation of amphiregulin's expression and receptor signaling may eventually prove to be an effective strategy in the treatment of hyperproliferative skin diseases.

Transgenic expression of the human amphiregulin gene induces a psoriasis-like phenotype

Amphiregulin (AR) is a heparin-binding, heparin-inhibited member of the epidermal growth factor (EGF) family and an autocrine growth factor for human keratinocytes. Previous studies have shown that AR expression is increased in psoriatic epidermis. To test the hypothesis that aberrant AR expression is central to the development of psoriatic lesions, we constructed a transgene (K14-ARGE) encoding a human keratin 14 promoter-driven AR gene. Our results indicate that transgene integration and subsequent expression of AR in basal keratinocytes correlated with a psoriasis-like skin phenotype. Afflicted mice demonstrated shortened life spans, prominent scaling and erythematous skin with alopecia, and occasional papillomatous epidermal growths. Histologic examination revealed extensive areas of marked hyperkeratosis with focal parakeratosis, acanthosis, dermal and epidermal lymphocytic and neutrophilic infiltration, and dilated blood vessels within the papillary dermis. Our results reveal that AR exerts activity in the skin that is distinct from that of transgenic transforming growth factor-alpha or other cytokines, and induces skin pathology with striking similarities to psoriasis. Our observations also link the keratinocyte EGF receptor-ligand system to psoriatic inflammation, and suggest that aberrant expression of AR in the epidermis may represent a critical step in the development or propagation of psoriatic lesions.

Adenosine and adenine nucleotides inhibit the autonomous and epidermal growth factor-mediated proliferation of cultured human keratinocytes

Previous investigations have shown disparate effects of adenine nucleotides on epidermal cell proliferation. Our present study demonstrates that adenosine and its related nucleotides (ATP, ADP, AMP) are antiproliferative for normal human epidermal keratinocytes cultured in the absence or presence of exogenous epidermal growth factor. Furthermore, the inhibitory effects of these compounds occur at concentrations less than 100 microM, are reversible, and do not affect the viability of the keratinocyte cultures. Our current investigation also demonstrates that both selective and nonselective adenosine receptor agonists are themselves approximately as potent as keratinocyte proliferation inhibitors, but are all less potent inhibitors than adenosine. These observations are consistent with the theory that adenosine mediates its antiproliferative response via a novel or more poorly characterized adenosine purinoreceptor subclass. Moreover, our present study demonstrates that ATP and ATP-gamma-S are significantly more potent antiproliferative agents than either alpha,beta-methylene ATP or beta,gamma-methylene ATP. Based on previous studies that have demonstrated that P2y purinoreceptors possess this type of ligand specificity and that the P2y purinoreceptor may be expressed by keratinocyte cultures, we propose that ATP may mediate its antiproliferative effects via this purinoreceptor. Collectively, our results indicate that adenosine and adenine nucleotides abrogate exogenous epidermal growth factor-dependent and -independent keratinocyte proliferation at submillimolar concentrations and may be important physiologic regulators of keratinocyte growth in vivo. Further, these results suggest that these or related compounds may have application as treatments for epidermal growth factor receptor-signaling pathway has been activated.

Carboxyl-terminal truncation of leucine76 converts heparin-binding EGF-like growth factor from a heparin-enhancible to a heparin-suppressible growth factor

Previous studies have indicated that heparin differentially regulates heparin-binding EGF-like growth factor (HB-EGF) and amphiregulin (AR) mitogenic activity. To further explore this phenomenon, these mitogens were compared under identical cell culture conditions in two different assays. The results of our present investigation demonstrated that AR-mediated mitogenic activity in the murine AKR-2B fibroblast-like cell line was inhibited by heparin, while HB-EGF activity was enhanced. However, the absolute effect of heparin appeared to be cell type specific since HB-EGF mitogenic activity was not dramatically affected by coincubation with heparin when tested on human dermal fibroblasts. Several studies have indicated that mutation of a conserved leucine in the carboxyl-terminal region of both EGF and transforming growth factor-alpha results in decreased affinity for EGF receptors. Since this leucine is present in the analogous position of HB-EGF, but absent in AR, we examined the effect of deleting this residue by carboxyl-terminal truncation of HB-EGF. Analysis of recombinant forms of HB-EGF demonstrated that HB-EGF can be converted to a heparin-inhibited growth factor if the putative mature form of the protein is truncated by two residues (leucine76 and proline77) at the carboxyl terminus. Further analysis demonstrated that only leucine76 appears to be required for heparin-dependent enhancement of HB-EGF-mediated mitogenic activity, indicating that this amino acid may play a pivotal role in controlling the response of HB-EGF to heparin or related glycosaminoglycan sulfates. Our results also suggest that expression of different HB-EGF forms in vivo could result in the production of HB-EGFs with divergent responses to sulfated glycosaminoglycans and proteoglycans.

Differential effects of a heparin antagonist (hexadimethrine) or chlorate on amphiregulin, basic fibroblast growth factor, and heparin-binding EGF-like growth factor activity

Amphiregulin (AR) and heparin-binding EGF-like growth factor (HB-EGF) are two recently identified members of the EGF family. Both AR and HB-EGF share with EGF the ability to interact with the type-1 EGF receptor; however, AR and HB-EGF differ from EGF in that both of these mitogens bind to heparin while EGF does not. To determine whether interactions with heparin-like molecules on the cell surface influence binding of AR and HB-EGF with EGF receptors and the subsequent mitogenic activity exerted by these growth factors, murine AKR-2B and Balb/MK-2 cells were treated with either an inhibitor of proteoglycan sulfation (chlorate) or a heparin antagonist (hexadimethrine). As expected, neither treatment significantly altered the specific binding of 125I-EGF on AKR-2B cells. Interestingly, treatment with either chlorate or hexadimethrine inhibited the ability of AR to compete with 125I-EGF for cell surface binding and also attenuated AR-mediated DNA synthesis. Thus, as has been suggested for other heparin-binding growth factors such as basic fibroblast growth factor (bFGF), the interaction of AR with an EGF-binding receptor appears to be facilitated by interaction with cell-associated sulfated glycosaminoglycans or proteoglycans. Unexpectedly, however, neither chlorate nor hexadimethrine treatment caused an inhibition of HB-EGF-induced mitogenic activity. Chlorate treatment did not significantly alter the ability of HB-EGF to compete with 125I-EGF for cell surface binding sites, however, heparin and hexadimethrine reduced the ability of HB-EGF to compete for 125I-EGF binding. These results suggest that, in AKR-2B cells, HB-EGF may mediate its mitogenic response at least in part through a receptor which appears to be selective for HB-EGF and permits HB-EGF-mediated mitogenic responses in the presence of hexadimethrine or heparin. Finally, hexadimethrine inhibited the specific binding and mitogenic activity of bFGF, suggesting that this cationic polymer can function as an antagonist of heparin-binding mitogens other than AR.

Autonomous growth of human keratinocytes requires epidermal growth factor receptor occupancy

In the studies reported here, we demonstrate that transforming growth factor alpha (TGF-alpha) or epidermal growth factor (EGF) is required for the establishment of small colonies of human keratinocytes at clonal densities, but once small (10-15 cells) colonies have formed, the continued growth of these colonies can proceed in the absence of exogenous TGF-alpha or EGF. Equivalent receptor-binding concentrations of TGF-alpha and EGF were equipotent in stimulating colony formation. We also demonstrate that the growth of keratinocytes at high densities proceeds in the absence of exogenous peptide growth factors or hormones. The expression of TGF-alpha mRNA and protein is regulated by both cell density and the presence of exogenous growth factors. The addition of an antibody which blocks the mitogenic effect of mature TGF-alpha had no effect on the autocrine/paracrine growth of these cells at either density. However, monoclonal antibodies which antagonize ligand activation of the EGF receptor inhibit the autonomous proliferation of keratinocytes at high density and abrogate the exogenous TGF-alpha/EGF-independent expansion of colonies at clonal density. The results of these experiments are among the first evidence to demonstrate that normal human epithelial cells in culture exhibit autocrine/paracrine-mediated proliferation. Exogenous growth factors initiate colonies of human keratinocytes that become self-perpetuating in culture. Keratinocytes regulate production of the mitogenic ligand, TGF-alpha, through a density-dependent mechanism, and cell density stringently controls proliferation.

Amphiregulin messenger RNA is elevated in psoriatic epidermis and gastrointestinal carcinomas

Amphiregulin (AR) is a heparin-regulated, epidermal growth factor-like growth factor capable of stimulating the proliferation of non-tumorigenic cells while inhibiting cell proliferation in some human tumor cell lines in vitro. In the present study, we have investigated AR mRNA expression in normal, hyperproliferative, and neoplastic human epithelium. Our results demonstrate that, compared with the adjacent uninvolved epithelium, AR mRNA expression is markedly elevated in epidermal biopsies derived from three human psoriatic lesions as well as in biopsies derived from five human colon carcinomas and three human stomach carcinomas. Moreover, analysis of a colon carcinoma by in situ hybridization revealed that AR mRNA is localized to the epithelium.

Inhibition of autonomous human keratinocyte proliferation and amphiregulin mitogenic activity by sulfated polysaccharides

We previously demonstrated that human keratinocyte cultures proliferate in the absence of polypeptide growth factors (autonomous growth) and that this autonomous growth is blocked by interaction of heparin with a human keratinocyte-derived autocrine factor (KAF) which we identified as amphiregulin (AR). In the present study, we demonstrate that sulfated polysaccharides other than heparin (low and high molecular weight dextran sulfates) also inhibit the AR-mediated autonomous proliferation of human keratinocytes. Furthermore, sulfated polysaccharides such as high and low molecular weight dextran sulfates, heparan sulfate and, to a lesser extent, chondroitin sulfates B and C were also shown to be inhibitors of human keratinocyte-derived AR (k-d AR)-stimulated DNA synthesis in quiescent murine AKR-2B cell cultures. Our results demonstrate that sulfation of polysaccharides is required for AR inhibitory activity, and that several sulfated polysaccharides (other than heparin) can act as inhibitors of AR-mediated autonomous proliferation in human epidermal keratinocytes and as inhibitors of k-d AR-mediated mitogenic activity in AKR-2B cells.

A heparin sulfate-regulated human keratinocyte autocrine factor is similar or identical to amphiregulin

A novel human keratinocyte-derived autocrine factor (KAF) was purified from conditioned medium by using heparin affinity chromatography as the first step. Purified KAF stimulated the growth of normal human keratinocytes, mouse AKR-2B cells, and a mouse keratinocyte cell line (BALB/MK). Heparin sulfate inhibited KAF mitogenic activity on all cell types tested and inhibited the ability of KAF to compete with epidermal growth factor for cell surface binding. Interestingly, KAF stimulated the growth of BALB/MK cells at high cell density but failed to stimulate these cells at clonal density. Protein microsequencing of the first 20 NH2-terminal amino acid residues of purified KAF revealed identity to the NH2 terminus of human amphiregulin (AR). Northern (RNA) blot analysis with AR-specific cRNA demonstrated that human keratinocytes, as well as mammary epithelial cell cultures, expressed high levels of AR mRNA. In contrast, AR mRNA was not detected in normal human fibroblasts or melanocytes and was present at reduced levels in several mammary tumor cell lines. The mitogenic activity of purified AR was also shown to be inhibited by heparin sulfate, and an AR-specific enzyme-linked immunosorbent assay (ELISA) revealed that KAF and AR are antigenically related. We have previously shown that human keratinocytes can grow in an autocrine manner. Our present study demonstrates that one of the growth factors responsible for this autocrine growth (KAF) is similar or identical to AR and that KAF and AR bioactivity can be negatively regulated by heparin sulfate.

Growth factor-independent proliferation of normal human neonatal keratinocytes: production of autocrine- and paracrine-acting mitogenic factors

When normal human foreskin keratinocytes were cultured in the absence of polypeptide growth factors at densities above 5 x 10(3)/cells cm2, the cells proliferated continuously and the addition of IGF-I, EGF, TGF alpha, bFGF, or aFGF did not significantly alter growth rate. Heparin sulfate, TGF beta, or suramin inhibited keratinocyte growth factor-independent proliferation. The addition of EGF, TGF alpha, or aFGF reversed heparin-induced growth inhibition, while bFGF partially negated this effect. RIA of keratinocyte-derived conditioned medium (CM) indicated the presence of TGF alpha peptide at a concentration of approximately 235 pg/ml. In contrast, clonal growth of keratinocytes required the addition of growth factors to the basal medium. Keratinocyte-derived CM replaced EGF in stimulating keratinocyte clonal growth, and an anti-EGF receptor mAb inhibited CM-induced keratinocyte clonal growth. In addition to its effect on keratinocytes, keratinocyte-derived CM stimulated the incorporation of [3H]thymidine by quiescent cultures of human foreskin fibroblasts, mouse AKR-2B cells, and EGF-receptorless mouse NR6 cells. CM-stimulated [3H]thymidine incorporation into quiescent normal human fibroblasts was partially reduced in the presence of anti-EGF receptor mAb. Heparin sulfate partially inhibited CM-induced keratinocyte clonal growth and [3H]thymidine incorporation into quiescent AKR-2B cells. We hypothesize from these data that autocrine and paracrine-acting factors produced by keratinocytes mediated their effect through the activation of both EGF receptor-dependent and EGF receptor-independent mitogenic pathways and that some of these factors appear to be sensitive to inhibition by heparin.

Expression and regulation of mRNA coding for acidic and basic fibroblast growth factor and transforming growth factor alpha in cells derived from human skin

We investigated the regulation of mRNAs coding for acidic fibroblast growth factor (aFGF), basic fibroblast growth factor (bFGF), and transforming growth factor-alpha (TGF alpha) in cultures of human neonatal foreskin fibroblasts, keratinocytes, and melanocytes. Each cell type was propagated in an optimized serum-free medium. In rapidly growing fibroblasts, the addition of fetal bovine serum caused a modest induction of aFGF message within 2 h in conjunction with a concomitant elevation of bFGF transcripts. In these same cells, TGF alpha mRNA could not be detected in any experimental condition. In contrast, keratinocytes rapidly growing in the presence of epidermal growth factor (EGF) contained transcripts for TGF alpha that increased substantially when these cells were treated with serum. This observation suggests that factors present in serum can elevate the levels of TGF alpha mRNA beyond the levels already present in keratinocyte cultures growing in the presence of EGF. These same keratinocyte cultures had low to undetectable levels of bFGF or aFGF message, and the levels of these mRNAs were not affected by serum treatment. Treatment of keratinocytes proliferating in the presence of EGF with TGF beta for 48 h caused expression of bFGF mRNA in four of six independent cell strains. TGF beta-enhanced expression of bFGF mRNA occurred as early as 12-24 h after TGF beta exposure. TGF beta did not enhance the expression of mRNA for aFGF or TGF alpha in keratinocytes. Melanocytes failed to express detectable levels of mRNA coding for any of these growth factors in the presence of absence of TGF beta or serum.(ABSTRACT TRUNCATED AT 250 WORDS)

Partial characterization of a glucocorticoid suppressible mitogenic activity secreted from a rat hepatoma cell line hypersensitive to the antiproliferative effects of glucocorticoids

We have previously shown that glucocorticoids suppress the proliferation of Fu5 hepatoma cells and have selected subclones which are either hypersensitive (BDS1) or resistant (EDR3) to the antiproliferative effects of dexamethasone, a synthetic glucocorticoid. BDS1 cells externalize a glucocorticoid suppressible mitogenic activity (denoted GSM) which stimulated [3H]thymidine incorporation in quiescent, serum-starved Balb/c 3T3 cells. Glucocorticoid treatment of BDS1 cells reduced the secreted levels of GSM activity by approximately 20-fold in comparison to untreated cells. The GSM activity was constitutively secreted from a glucocorticoid receptor minus variant (EDR3) demonstrating that the suppression of this mitogenic activity is a new glucocorticoid hormone response which required a functional receptor. GSM activity was sensitive to sulfhydryl reducing agents or trypsin, stable to heat and acid treatments and fractionated in gel filtration columns with a native molecular weight of approximately Mr 30,000. The persistence of this size for mitogenic activity after electrophoretic fractionation in nonreducing sodium dodecyl sulfate-poly-acrylamide gels suggested that the GSM activity is comprised of a single protein. Total secreted protein isolated from untreated BDS1, but not dexamethasone-treated BDS1, stimulated 3T3 cells to grow in transformed-appearing large colonies in soft agar and to display multiple layering and elongated spindle-like morphology on solid substratum. The addition of both insulin and EGF to conditioned medium protein isolated from glucocorticoid-treated BDS1 cells restored full induction of 3T3 cell anchorage-independent growth while insulin restored full and EGF partial mitogenic stimulation of these fibroblasts. These results suggest that the GSM activity acts in a pathway common to that of insulin or EGF in fibroblasts.

Glucocorticoids confer normal serum/growth factor-dependent growth regulation to Fu5 rat hepatoma cells in vitro. Sequential expression of cell cycle-regulated genes without changes in intracellular calcium or pH

Glucocorticoid hormones induced a stringent dependence on serum for the in vitro proliferation of Fu5 rat hepatoma cells by suppressing the growth rate and final quiescent cell density. Treatment of dexamethasone-suppressed quiescent Fu5 with serum plus insulin caused a rapid reinitiation of cellular proliferation and DNA synthesis that peaked at 16 h. RNA dot blot analysis of this time course showed that the transcript levels for the proto-oncogenes c-fos, c-myc, and c-rasKi peaked at 0.5, 2, and 4 h, respectively, while expression of c-rasHa and ornithine decarboxylase transcripts rose steadily during 16 h. Microspectrofluorimetric measurements of cytosolic calcium (Ca2+i) with fura-2 showed that insulin and serum, alone or in combination, elicited no changes in Ca2+i over a 50-min time course, although ATP, which is not a mitogen, induced large increases in Ca2+i. Cytosolic pH, pHi, was also measured using 2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein. Insulin and serum, alone or in combination, did not cause pHi to increase in either 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES) (pHi 7.17)- or HCO3/CO2 (pHi 7.19)- buffered media. Acid-loading of cells with NH4Cl indicated that both quiescent and proliferating Fu5 cells have equally active, amiloride-sensitive Na/H exchangers. Therefore, induction of DNA synthesis and proto-oncogene expression occurs in Fu5 epithelial tumor cells in the absence of any short term increases of pHi or Ca2+i.

Glucocorticoid receptor-dependent inhibition of cellular proliferation in dexamethasone-resistant and hypersensitive rat hepatoma cell variants

Exposure of the Fu5 rat hepatoma cell line to glucocorticoids, such as dexamethasone and hydrocortisone, suppressed the growth rate and final density of cells grown in the presence of serum. This hormonal effect was proportional to receptor occupancy and affinity and, in addition, the glucocorticoid antagonist RU38486 prevented this response. Two classes of dexamethasone-resistant variants that failed to be growth inhibited were recovered from ethyl methylsulfonate-mutagenized populations by continuous culture in the presence of 1 microM dexamethasone. The first class, represented by the EDR3 subclone, was completely glucocorticoid unresponsive and failed to express receptor transcripts. The second class, represented by the EDR1, EDR5, and EDR7 subclones, possessed significant levels of glucocorticoid receptor but were only partially glucocorticoid responsive when stimulated with saturating levels of hormone. Introduction of functional glucocorticoid receptor genes into both classes of dexamethasone-resistant variants by a recombinant retrovirus expression vector restored glucocorticoid responsiveness and suppression of cell growth. A hypersensitive variant (BDS1), recovered by bromodeoxyuridine selection, was fully glucocorticoid responsive, and its inhibition of proliferation was more acutely regulated by dexamethasone. Taken together, our results established that the inhibition of proliferation in Fu5 rat hepatoma cells represents a new glucocorticoid response that requires the expression of a functional glucocorticoid receptor.

Genetic evidence that the steroid-regulated trafficking of cell surface glycoproteins in rat hepatoma cells is mediated by glucocorticoid-inducible cellular components

The biological control of posttranslational maturation and compartmentalization reactions that operate upon proteins during transport to their final cellular destinations is crucial for normal cellular function. Using the expression of mouse mammary tumor virus (MMTV) glycoproteins as sensitive probes in the viral-infected rat hepatoma cell line M1.54, we have discovered and documented a novel glucocorticoid-regulated trafficking pathway that controls the cell surface localization of MMTV glycoproteins. One complement-selected derivative of M1.54 cells, CR4, failed to compartmentalize cell surface MMTV glycoproteins in the presence of dexamethasone. To test genetically if this glycoprotein trafficking pathway is mediated by cellular or viral gene products, CR4 cells were fused with uninfected Fu5 rat hepatoma cells. Indirect immunofluorescence of CR4 X Fu5 heterokaryons revealed that Fu5 complemented the defect in CR4 only after exposure to 1 microM dexamethasone. The glucocorticoid inhibition of Fu5 proliferation was exploited to recover the receptor-deficient uninfected derivative EDR3 that expressed a 100-fold lower level of [3H]dexamethasone binding activity. Analysis of CR4 X EDR3 cell fusions by indirect immunofluorescence revealed that EDR4 cells complemented CR4 in a dexamethasone-dependent manner, suggesting that EDR3 supplied a functinal trafficking component while CR4 provided a functional glucocorticoid receptor to the heterokaryons. Taken together, our results demonstrate that cellular-encoded glucocorticoid-inducible components mediate the regulated trafficking of cell surface MMTV glycoproteins.

Highly sensitive immunoadsorption procedure for detection of low-abundance proteins

A procedure that virtually eliminates nonspecific adsorption of radiolabeled proteins during immunoprecipitation was devised utilizing staphylococcal cells containing protein A (Staph A). Immunoprecipitates (antigen-antibody complexes) were solubilized from Staph A pellets into detergent micelles by incubation in a small volume of 1% sodium dodecyl sulfate (SDS) at 23 degrees C for 10 min. To allow re-formation of immunocomplexes and rebinding to new Staph A, the SDS-solubilized material was diluted 20-fold in buffer containing 1% Triton X-100 and 0.5% sodium deoxycholate. Specific conductance measurements revealed that this solubilization and subsequent reimmunoadsorption of antibody-antigen complexes occur at SDS concentrations that are first above and then below its critical micelle concentration. This procedure lowered the nonspecific background from approximately 2250 parts per million (ppm) to less than 25 ppm with a final recovery of 30-50% depending on the antigen and antibody. Chaotropic agents such as 2 M urea, 0.2 M KOH, and 3.5 M MgCl2 (as well as combinations of urea and SDS) can substitute for 1% SDS, although the final recovery is somewhat lower. Fluorography of radiolabeled proteins obtained in this manner displays virtually undetectable background even for exposures as long as 2 months. These methods allowed the unambiguous detection of low-abundance antigens at a high level of sensitivity, for example, mouse mammary tumor virus protein products and epidermal growth factor receptor.

Field cases of aflatoxicosis in pigs

Five cases of aflatoxicosis in pigs in southern Queensland are described. One peracute case where aflatoxin concentrations of up to 5000 micrograms aflatoxin B1/kg were demonstrated in stomach contents was presumed to be caused by consumption of mouldy bread. High levels of toxins were also present in the livers. Two cases of acute toxicity were caused by feeding mouldy peanut screenings containing 22000 micrograms aflatoxin B1/kg. One case of subacute and one of chronic toxicity were caused by sorghum grain based rations with lower aflatoxin levels (4640 and 255 micrograms/kg). Peracute toxicity caused collapse and deaths within several hours, acute toxicity caused deaths within 12 h and with subacute toxicity deaths occurred after 3 weeks on a toxic ration. Anorexia and ill thrift affecting only growing animals were seen with chronic toxicity. Extensive centrilobular liver necrosis and haemorrhage occurred with peracute toxicity and in cases of acute poisoning there was hepatic centrilobular cellular infiltration, hepatocyte swelling and bile stasis. With subacute toxicity hepatocyte vacuolation together with bile stasis and bile ductule hyperplasia were seen.

A CYTOCHEMICAL STUDY OF ACID PHOSPHATASE AND NUCLEASE ACTIVITY IN THE PLASTID OF CLOSTERIUM ACEROSUM(1)

Acid phosphatase activity in Closterium acerosum has been studied using the Gomori and the azo dye procedures. A modification of the Gomori method was used for detecting the distribution of acid nucleases. The plastid is the major site of acid phosphatase activity luhich may be primarily within pyrenoids, between pyrenoids, or throughout the plastid. The Gomori procedure showed activity within the pyrenoids or in the central core of the plastid, whereas the azo dye method showed activity throughout with an occasional tendency to be localized near the ends. No other cytoplasmic activity was ob-served but evidence for occasional activity in the nucleus is presented. Alkaline phosphatase could not be detected. Acid nuclease activity, which results in the degradation of DNA, RNA, and RNA-Core, has been found in both the nucleus and the plastid. Plastid activity is heat labile, whereas nuclear activity is only slightly diminished after 5 min at 100 C. The results arc interpreted as indicating at least 2 acid phosphatases and 2 nucleases in C. acerosum. The findings are discussed with respect to the distribution of similar enzymes in other organisms.