Transmission of HIV-1 in infants born to seropositive mothers: PCR-amplified proviral DNA detected by flow cytometric analysis of immunoreactive beads

Serodiagnosis of human plague by a combination of immunomagnetic separation and flow cytometry

BACKGROUND

Plague is a severe, highly communicable bacterial disease caused by Yersinia pestis. It is still endemic in more than 20 countries worldwide. Although known as a devastating disease for centuries, laboratory confirmation of clinical suspected cases is still problematic. No standardized and internationally approved test system is commercially available. The aim of this study was the introduction and evaluation of a combination of immunomagnetic separation and flow cytometry for the serodiagnosis of human plague.

METHODS

Paramagnetic polystyrene beads were coated with purified F1 capsular antigen (F1 CA) and reacted with sera from plague patients, from 26 laboratory personnel vaccinated against plague and from 102 healthy blood donors (HBD). After incubation with fluorescein isothiocyanate-conjugated anti-human rabbit IgG, particle-associated fluorescence was detected by flow cytometry.

RESULTS

Anti-F1 CA antibodies could be demonstrated in all patients with bacteriologically confirmed plague and in 22 sera (84.6%) from vaccinees. Only one serum in the HBD group showed a weakly positive reaction. The total assay time was less than 2 h.

CONCLUSIONS

Compared with a recently published combination of an anti-F1 CA enzyme-linked immunosorbent assay (ELISA) and immunoblot, the new assay showed the same sensitivity as the ELISA and almost the same specificity (99.0 versus 100%) as the immunoblot. Allowing a rapid, reliable, and quantitative analysis, immunomagnetic separation combined with flow cytometry might replace both conventional immunoassays.

Multiplexed microsphere-based flow cytometric assays

Flow cytometry has become an indispensable tool for clinical diagnostics and basic research. Although primarily designed for cellular analysis, flow cytometers can detect any particles in the lower micron range, including inert microspheres of different sizes, dyed with various fluorochromes. Over the past 20 years, microspheres have been used as calibrators for flow cytometers and also as a solid support for numerous molecular reactions quantitated by flow cytometry. Proteins, oligonucleotides, polysaccharides, lipids, or small peptides have been adsorbed or chemically coupled to the surface of microspheres to capture analytes that are subsequently measured by a fluorochrome-conjugated detection molecule. More recently, assays for similar analytes have been multiplexed, or analyzed in the same assay volume, by performing each reaction on a set of microspheres that are dyed to different fluorescent intensities and, therefore, are spectrally distinct. Some recent applications with fluorescent microspheres have included cytokine quantitation, single nucleotide polymorphism genotyping, phosphorylated protein detection, and characterization of the molecular interactions of nuclear receptors. The speed, sensitivity, and accuracy of flow cytometric detection of multiple binding events measured in the same small volume have the potential to replace many clinical diagnostic and research methods and deliver data on hundreds of analytes simultaneously.

Flow cytometry: an 'old' tool for novel applications in medical genetics

Flow cytometry was originally established as an automated method for measuring optical or fluorescence characteristics of cells or particles in suspension. In the meantime, flow cytometers have become user-friendlier, less expensive instruments with an increasing importance in clinical diagnostics. Besides the classical fields of application, such as immunophenotyping blood cells or analyzing the cell cycle status by measuring the DNA content, novel flow cytometric methods have been developed to identify and to quantify disease-related gene sequences. Here we give an overview of current and future applications, including the detection of viral sequences via microsphere-based PCR assays and the analysis of single nucleotide polymorphisms, reflecting individual phenotypic traits. Furthermore, flow cytometry allows the quantification of gene expression changes as well as the isolation of differentially expressed gene sequences. Flow cytometry is also convenient for multiplex analyses, e.g. when hybridizing DNA samples to a mixture of various microsphere populations each coated with different DNA probes. Last but not least, the use of magnetic beads in combination with flow cytometers coupled with automated devices enables molecular diagnostics on a large scale. Overall, this review demonstrates flow cytometry as a rapid, sensitive, and reproducible tool applicable to a wide range of medical genetic approaches.

Flow Cytometric Analysis of Reverse Transcription-PCR Products: Quantification of p21WAF1/CIP1 and Proliferating Cell Nuclear Antigen mRNA

Background: Reverse transcription-PCR (RT-PCR) is a powerful tool in clinical diagnostics for analyzing even small amounts of RNA, but sensitive assays for quantifying the amplification products are time-consuming or expensive. Here we describe a novel flow cytometry-based assay for rapid and sensitive determination of relative amounts of RT-PCR products.

Methods: For flow cytometric quantification, PCR products were labeled with both digoxigenin and biotin during amplification. Subsequently, amplicons were simultaneously bound to anti-digoxigenin microparticles and fluorescently labeled with streptavidin-R-phycoerythrin. Fluorescence intensity per bead was determined by flow cytometry. To study this assay, we examined the expression of the p21WAF1/CIP1 gene and the proliferating cell nuclear antigen (PCNA) gene in ultraviolet irradiation-exposed human keratinocytes lacking functional p53.

Results: Fluorescence was linear with 60–10 000 pg of PCR product. As little as 0.4 fmol (40 pg of a 163-bp amplicon) of PCR product could be distinguished from background. The between-run CV of the fluorescent signal for 10 ng of p21 cDNA was 12% (n = 10). The fluorescence-template curve was sigmoidal. p21WAF1/CIP1 mRNA was decreased after ultraviolet irradiation of keratinocytes, whereas PCNA mRNA was markedly increased.

Conclusion: The flow cytometric assay permits rapid (25 min) and reproducible identification of changes in mRNA abundance.

Analysis of virus-infected cells by flow cytometry

Flow cytometry has been used to study virus-cell interactions for many years. This article critically reviews a number of reports on the use of flow cytometry for the detection of virus-infected cells directly in clinical samples and in virus-infected cultured cells. Examples are presented of the use of flow cytometry to screen antiviral drugs against human immunodeficiency virus (HIV), human cytomegalovirus, and herpes simplex viruses (HSV) and to perform drug susceptibility testing for these viruses. The use of reporter genes such as green fluorescent protein incorporated into HIV or HSV or into cells for the detection of the presence of virus, for drug susceptibility assay, and for viral pathogenesis is also covered. Finally, studies on the use of flow cytometry for studying the effect of virus infection on apoptosis and the cell cycle are summarized. It is hoped that this article will give the reader some understanding of the great potential of this technology for studying virus cell interactions.

Applications of flow cytometry to clinical microbiology

Classical microbiology techniques are relatively slow in comparison to other analytical techniques, in many cases due to the need to culture the microorganisms. Furthermore, classical approaches are difficult with unculturable microorganisms. More recently, the emergence of molecular biology techniques, particularly those on antibodies and nucleic acid probes combined with amplification techniques, has provided speediness and specificity to microbiological diagnosis. Flow cytometry (FCM) allows single- or multiple-microbe detection in clinical samples in an easy, reliable, and fast way. Microbes can be identified on the basis of their peculiar cytometric parameters or by means of certain fluorochromes that can be used either independently or bound to specific antibodies or oligonucleotides. FCM has permitted the development of quantitative procedures to assess antimicrobial susceptibility and drug cytotoxicity in a rapid, accurate, and highly reproducible way. Furthermore, this technique allows the monitoring of in vitro antimicrobial activity and of antimicrobial treatments ex vivo. The most outstanding contribution of FCM is the possibility of detecting the presence of heterogeneous populations with different responses to antimicrobial treatments. Despite these advantages, the application of FCM in clinical microbiology is not yet widespread, probably due to the lack of access to flow cytometers or the lack of knowledge about the potential of this technique. One of the goals of this review is to attempt to mitigate this latter circumstance. We are convinced that in the near future, the availability of commercial kits should increase the use of this technique in the clinical microbiology laboratory.

Applications of flow cytometry to clinical microbiology

Classical microbiology techniques are relatively slow in comparison to other analytical techniques, in many cases due to the need to culture the microorganisms. Furthermore, classical approaches are difficult with unculturable microorganisms. More recently, the emergence of molecular biology techniques, particularly those on antibodies and nucleic acid probes combined with amplification techniques, has provided speediness and specificity to microbiological diagnosis. Flow cytometry (FCM) allows single- or multiple-microbe detection in clinical samples in an easy, reliable, and fast way. Microbes can be identified on the basis of their peculiar cytometric parameters or by means of certain fluorochromes that can be used either independently or bound to specific antibodies or oligonucleotides. FCM has permitted the development of quantitative procedures to assess antimicrobial susceptibility and drug cytotoxicity in a rapid, accurate, and highly reproducible way. Furthermore, this technique allows the monitoring of in vitro antimicrobial activity and of antimicrobial treatments ex vivo. The most outstanding contribution of FCM is the possibility of detecting the presence of heterogeneous populations with different responses to antimicrobial treatments. Despite these advantages, the application of FCM in clinical microbiology is not yet widespread, probably due to the lack of access to flow cytometers or the lack of knowledge about the potential of this technique. One of the goals of this review is to attempt to mitigate this latter circumstance. We are convinced that in the near future, the availability of commercial kits should increase the use of this technique in the clinical microbiology laboratory.

Antiviral drug susceptibility assays: going with the flow

This review describes the procedures for the use of fluorochrome labeled monoclonal antibodies and flow cytometry for the detection and quantification of virus infected cells. The application of this technology for (1) identifying virus infected cells in clinical specimens obtained from human cytomegalovirus (HCMV) and human immunodeficiency virus (HIV) infected individuals; (2) screening antiviral compounds active against HCMV, HDSV and HIV; and (3) performing drug susceptibility testing for HCMV, HSV and HIV clinical isolates are reviewed. The flow cytometry drug susceptibility assay is rapid, quantitative, and easily performed. It should be considered by anyone interested in performing drug susceptibility testing for any virus for which there are reliable monoclonal antibodies.

Rapid amperometric verification of PCR amplification of DNA

Amplification of an 800-base template was verified in a 10-min test on a 2-microL sample of the PCR product solution. For verification, digoxigeninylated primers and biotinylated d-UTP-16-biotin were added to the amplification solution. The resulting amplified product was digoxigeninlabeled at its 3'-end and was also labeled with multiple biotin functions along its chain. The detecting electrode was coated with an electron-conducting redox hydrogel to which anti-digoxin monoclonal antibody was covalently bound. The amplified DNA was captured by the electrode through conjugation of its 3'-digoxigenin with the antibody. Exposure to a solution of horseradish peroxidase-labeled avidin led to capture of the enzyme and switched the redox hydrogel from a noncatalyst to catalyst for H2O2 electroreduction. The switching resulted in an H2O2 electroreduction current density of 2.1 +/- 0.9 microA cm-2 in 10-4 M H2O2 at Ag/AgCl potential and at 25 degrees C.

Neutralizing antibodies against HIV determined by amplification of viral long terminal repeat sequences from cells infected in vitro by nonneutralized virions

Based on the earliest intracellular synthesis of nascent HIV-1 long terminal repeat (LTR) fragments, we have established a heminested polymerase chain reaction (HNPCR) amplification of the 5' LTR sequences (LTR-HNPCR) for molecular assay of virus-neutralizing antibodies (VNAb). We incubated HIV antibodies with virus isolates for an hour, followed by addition of lymphoid cells (H9 or peripheral blood mononuclear cells [PBMC]) and further incubation for an hour. After washing the cells three times for thorough removal of free virions and antibodies, LTR-HNPCR consistently revealed HIV DNA in H9 cells after 15 minutes, in PBMC after 4 hours, and corresponding virion expression after 7 days in culture. Replication-competent HIV detected by LTR-HNPCR following overnight culture of infected PBMC for 16 to 18 hours was comparable with tissue culture infectivity measured by p24 antigen expression at 7 days. After establishing a molecular assay for in vitro HIV neutralization by HIV Ig, a panel of five HIV isolates tested with 6 monoclonal antibodies and HIV Ig revealed that LTR-HNPCR was comparable with other VNAb assays. These preliminary data indicate that the molecular assay for HIV neutralization has a clear-cut end point, is specific, reliable, and more rapid than other VNAb assays. Therefore, it offers potential utility in evaluating immune response to candidate vaccines.