Comparison of MRC-5 and HFF cells for the identification of cytomegalovirus in centrifugation culture

Immunological Detection and Characterization

Immunological methods have been used for viral diagnosis for more than 100 years. Although molecular methods are replacing many older methods of viral diagnosis, there is still a significant role for immunological methods to guide patient care and in the performance of epidemiologic studies. Identification of viral antigens in clinical samples can be accomplished rapidly through the use of point-of-care lateral immunoassays or through the use of more traditional immunofluorescence and enzyme immunoassays in the virology laboratory. Serological assays are also a valuable tool for the clinician and epidemiologist. Many of the available diagnostic assays have enzyme immunoassay formats, but functional assays such as hemagglutination-inhibition and neutralizing antibody tests are also available. In some instances, virus infection can be diagnosed with a single serum sample (e.g., HIV and hepatitis C virus infections) while in other instances paired sera are needed (e.g., those caused by common respiratory viruses). Point-of-care antibody assays are also available for testing blood and saliva samples for some viruses. An understanding of the principles of immunological detection methods is important in the application and interpretation of test results.

Novel microneutralization assay for HCMV using automated data collection and analysis

In addition to being sensitive and specific, an assay for the assessment of neutralizing antibody activity from clinical trial samples must be amenable to automation for use in high-volume screening. To that effect, we developed a 96-well microplate assay for the measurement of HCMV-neutralizing activity in human sera using the HCMV-permissive human cell line HEL-299 and the laboratory strain of HCMV AD169. The degree to which neutralizing antibodies diminish HCMV infection of cells in the assay is determined by quantifying the nuclei of infected cells based on expression of the 72 kDa IE1 viral protein. Nuclear IE1 is visualized using a highly sensitive immunoperoxidase staining and the stained nuclei are counted using an automated ELISPOT analyzer. The use of Half Area 96-well microplates, with wells in which the surface area of the well bottom is half the area of a standard 96-well microplate plate, improves signal detection compared with standard microplates and economizes on the usage of indicator cells, virus, and reagents. The staining process was also streamlined by using a microplate washer and data analysis was simplified and accelerated by employing a software program that automatically plots neutralization curves and determines NT₅₀ values using 4-PL curve fitting.

The optimized assay is not only fast and convenient, but also specific, sensitive, precise and reproducible and thus has the characteristics necessary for use in measuring HCMV-neutralizing activity in the sera of vaccine trial subjects such as the recipients of Vical's HCMV pDNA vaccine candidates.

Physical and chemical methods for enhancing rapid detection of viruses and other agents

Viral replication events can be enhanced by physical, chemical, or heat treatment of cells. The centrifugation of cells can stimulate them to proliferate, reduce their generation times, and activate gene expression. Human endothelial cells can be activated to release cyclo-oxygenase metabolites after rocking for 5 min, and mechanical stress can stimulate endothelial cells to proliferate. Centrifugation of virus-infected cultures can increase cytopathic effects (CPE), enhance the number of infected cells, increase viral yields, and reduce viral detection times and may increase viral isolation rates. The rolling of virus-infected cells also has an effect similar to that of centrifugation. The continuous rolling of virus-infected cultures at < or = 2.0 rpm can enhance enterovirus, rhinovirus, reovirus, rotavirus, paramyxovirus, herpesvirus, and vaccinia virus CPE or yields or both. For some viruses, the continuous rolling of infected cell cultures at 96 rpm (1.9 x g) is superior to rolling at 2.0 rpm for viral replication or CPE production. In addition to centrifugation and rolling, the treatment of cells with chemicals or heat can also enhance viral yields or CPE. For example, the treatment of virus-infected cells with dimethyl sulfoxide can enhance viral transformation, increase plaque numbers and plaque size, increase the number of cells producing antigens, and increase viral yields. The infectivity of fowl plague virus is increased by 80-fold when 4% dimethyl sulfoxide is added to culture medium immediately after infection. The heat shocking of virus-infected cells also has been shown to have a stimulatory effect on the replication events of cytomegalovirus, Epstein-Barr virus, and human immunodeficiency virus. The effects of motion, chemicals, or heat treatments on viral replication are not well understood. These treatments apparently activate cells to make them more permissive to viral infection and viral replication. Perhaps heat shock proteins or stress proteins are a common factor for this enhancement phenomenon. The utility of these treatments alone or in combination with other methods for enhancing viral isolation and replication in a diagnostic setting needs further investigation.

Comparison of shell vial culture and the suspension-infection method for the rapid detection of herpes simplex viruses

Shell vial culture (SVC) and suspension-infection (SI) (simultaneous seeding of culture cells and inoculation of sample) were compared for the detection of herpes simplex virus (HSV) in clinical specimens. Conventional culture methods using mink lung cells or the Vero cell subline C1008 were also compared with each other and with SVC and SI. Additionally, SVC and SI were compared for quantitative determination of HSV infectivity. Compared with conventional culture with mink lung cells, culture with C1008 cells was 98% sensitive, and the sensitivities of SVC and SI were 94% and 93%, respectively. In quantitative determinations, titers of infectious HSV in positive clinical samples were a mean of five- to six-fold higher, as detected in SVC compared with SI titrations. For quantitative detection of infectious HSV, SVC was more sensitive than SI; however, for diagnosis of HSV in clinical specimens, no significant difference was observed between SI and SVC.

A rapid culture alternative to the shell-vial method for the detection of herpes simplex virus

The rapid test for detection of herpes simplex virus (HSV) in clinical specimens based on infection of cells in suspension (SI test) was compared to the shell-vial culture (SVC) method and conventional culture. Mink lung cells were used throughout the study. Detection of HSV was not significantly different whether using SI or SVC. The sensitivity of SI in detecting HSV, when compared with conventional culture, was 93.0% using 0.1 ml inocula and 98.3% using 0.5 ml inocula. The time to obtain a final result with both SI and SVC was 1 day compared with 1-7 days by conventional culture. The SI method detected both HSV type-1 and HSV type-2 clinical isolates. The SI technique is a simple method for the rapid detection of HSV and can yield diagnostic results with a minimum of technical manipulations.

Detection of human cytomegalovirus in clinical specimens by centrifugation culture with a nonhuman cell line

The sensitivities of MRC-5 and mink lung (ML) cells in centrifugation culture were compared simultaneously for the detection of cytomegalovirus (CMV) IE antigen (immediate-early antigen) from clinical specimens. Of 413 samples assayed, 51 (12%) were positive for CMV by both centrifugation and standard cell culture. At 20 h postinoculation (p.i.), 46 of 51 (90.2%) CMV-positive specimens were detected in ML cells. At 40 h p.i., 50 of 51 (98.0%) CMV-positive specimens were detected in ML cells, compared with 48 of 51 (94.0%) in MRC-5 cells. There was no significant difference in the detection of CMV in either cell line by centrifugation culture. However, in 19 of 23 positive samples that had countable foci at 20 h p.i., there was a 25% increase in the number of positive foci observed for ML cells compared with MRC-5 cells. Less toxicity was also noted for ML cells than for MRC cells, particularly in viral blood specimens. These data suggest that ML cells are comparable to MRC-5 cells for the rapid detection of CMV by centrifugation culture.

Comparison of MRC-5 and U-373MG astrocytoma cells for detection of cytomegalovirus in shell vial centrifugation cultures

U-373MG astrocytoma cells are susceptible to human cytomegalovirus (CMV) infection and offer the advantage of a continuous cell line for clinical laboratory use. U-373MG to MRC-5 cells for detection of CMV by centrifugation culture were therefore compared. At 20 h, 10 (6.1%) versus 12 (7.4%) of 163 clinical specimens were positive for CMV, and at 40 h, 12 (7.4%) versus 17 (10.4%) were positive in U-373MG and MRC-5 cells, respectively. Substantial toxicity was found in U-373MG cells (84%) when inoculated with blood specimens. For detection of CMV in centrifugation culture, MRC-5 cells are superior due both to higher sensitivity and lesser toxicity.

Suitability of infection of cells in suspension for detection of herpes simplex virus

Detection of herpes simplex virus in clinical specimens by the suspension-infection technique was compared with detection by conventional cell culture. The sensitivity and specificity of the suspension-infection technique compared with those of conventional culture were 95.9 to 98.2% and 97.5 to 100%, respectively, depending on the cell line used in the tests. The mean time to diagnosis by the suspension-infection technique was 1 day, compared with 4.8 days by conventional culture. Comparable detection of low-level positive specimens was observed with the methods. In a clinical setting, the isolation rates obtained by suspension-infection and conventional culture were indistinguishable. These results indicate that the suspension-infection method can be used for the detection of herpes simplex virus and can yield rapid diagnostic results without a time-consuming centrifugation step.

Mechanisms of cytomegalovirus-mediated myelosuppression: perturbation of stromal cell function versus direct infection of myeloid cells

Infection with cytomegalovirus (CMV) continues to be one of the most common complications following allogeneic bone marrow transplantation. To study the role of CMV in the suppression of hemopoiesis that frequently accompanies infection, we investigated the effect of CMV on the growth of isolated committed myeloid progenitors and on hemopoiesis in long-term bone marrow cultures. Laboratory strain AD169 had no effect on the growth and development of progenitor cells. In contrast, 40% of clinical isolates of CMV inhibited colony formation by up to 100%. In long-term bone marrow cultures all CMV isolates resulted in myelosuppression, which in the majority of cases was associated with the infection of stromal elements. Analysis of RNA from stromal cells infected with AD169 and one clinical isolate demonstrated a specific deficiency of granulocyte colony-stimulating factor transcripts. For a small proportion of the clinical isolates tested in long-term bone marrow cultures, suppression of hemopoiesis was correlated with infection of developing granulocytes. These studies suggest that CMV can impair hemopoiesis either through infection of stromal cells and consequent perturbation of growth factor production or by direct infection of myeloid cells.

Continuous high-speed rolling versus centrifugation for detection of herpes simplex virus

Specimens submitted for diagnosis of herpes simplex virus infections were inoculated into shell vials and conventional culture tubes. Inoculated culture tubes were incubated with rolling at 96 rpm. Immunoperoxidase (IP) staining and cytopathic effects (CPE) were used to detect positive cultures. At 24 h, 42 (53%) of the rolled cultures were positive for CPE, while only 16 (21%) of the shell vials were CPE positive (P less than 0.01). No difference in sensitivity was seen between rolled and shell vial cultures that were inoculated with high-titered viral preparations and IP stained at 16 h. However, when low-titered preparations were used, 39 of 41 (95%) were IP positive by the high-speed roller method at 64 h postinoculation, while only 24 of 41 (58%) were IP positive with shell vials (P less than 0.01). These results indicate that high-speed roller method at 64 h postinoculation, while only 24 of 41 (58%) were IP positive with shell vials (P less than 0.01). These results indicate that high-speed rolling is better than the shell vial technique for the detection of herpes simplex virus by IP staining.

Rapid detection of cytomegalovirus in bronchoalveolar lavage specimens from marrow transplant patients: evaluation of a direct fluorescein-conjugated monoclonal antibody reagent

An FITC-conjugated monoclonal antibody reagent containing three CMV-specific monoclonal antibodies was evaluated for the rapid detection of CMV in bronchoalveolar lavage (BAL) cytospin preparations by direct IF (DFA). Eighty-six BAL samples from 72 marrow transplant patients were inoculated into both centrifugation and standard cell culture. CMV was detected in 49/86 (57%) BAL samples. DFA detected 37/46 (80%) samples which were positive in centrifugation culture. While DFA staining lacked the sensitivity (overall sensitivity 38/49, 78%) to replace either standard or centrifugation culture, the total laboratory time needed to complete the DFA was only 1.5 h and its concurrent use with centrifugation culture can provide rapid specific diagnosis of CMV pneumonia.

Direct detection of cytomegalovirus from bronchoalveolar lavage samples by using a rapid in situ DNA hybridization assay

An in situ DNA hybridization assay was compared with centrifugation culture for rapid detection of cytomegalovirus (CMV) from bronchoalveolar lavage (BAL) samples. Eighty BAL samples were inoculated into both centrifugation culture and standard culture. Cytospin preparations of the BAL samples were studied in a 75-min in situ DNA hybridization assay using the PathoGene CMV kit (Enzo Biochem, Inc., New York, N.Y.). Of the 80 samples, 39 (49%) were positive for CMV; 37 of 39 (95%) were positive by centrifugation culture, 34 of 39 (87%) were positive in standard culture, 24 of 39 (62%) were positive by in situ hybridization, and 20 of 39 (56%) were positive by histologic and/or immunofluorescence techniques. The in situ hybridization assay detected 23 of the 37 samples positive in centrifugation culture, for a sensitivity of 62% and a specificity of 98%. We conclude that the in situ hybridization assay is a specific and more rapid test than centrifugation culture and standard culture for diagnosis of CMV pulmonary infection. For the clinical laboratory, however, current hybridization methods are not sufficiently sensitive to replace centrifugation culture for detection of CMV in BAL specimens.

Effect of high-speed rolling on herpes simplex virus detection and replication

We examined the effect of high-speed rolling on herpes simplex virus replication. Inoculated cultures were rolled at 2, 96, or 383 rpm, while stationary cultures served as controls. At 24 h, inoculated cultures rolled at 96 rpm had a 6.8-fold increase in foci when compared with stationary cultures (P less than 0.01) and a 2.8-fold increase over cultures rolled at 2 rpm (P less than 0.05). Cultures rolled at 2 rpm had a 2.4-fold increase in foci over stationary cultures (P less than 0.05). Viral yield results correlated with focus results. Significantly more virus was present in cultures rolled at 96 rpm (7.3-fold) than in stationary cultures. Cultures rolled at 2 rpm produced 2.9-fold more virus than stationary cultures (P less than 0.05). Of 37 cultures rolled at 96 rpm, 33 (89%) were cytopathic effect positive at 96 h, while 18 of 40 (45%) were positive at 2 rpm and only 2 of 37 (5%) were positive for stationary cultures (P less than 0.01). Cultures rolled at 96 rpm produced maximum viral yields 2 days sooner than stationary cultures. Rolling of inoculated cultures should be used in the clinical laboratory to aid in the rapid detection of herpes simplex virus.

Comparison of two rapid culture methods for detection of cytomegalovirus in clinical specimens

The conventional virus isolation technique was compared with a 24-h shell vial centrifugation culture technique and with a 48-h tube culture method for the detection of cytomegalovirus (CMV) in MRC-5 cells. Of 200 clinical specimens tested, 41 were positive for CMV by at least one procedure. Indirect immunoperoxidase staining was positive for 32 (78.0%) of 41 specimens in the tube culture method and for 30 (73.2%) of 41 specimens in the shell vial centrifugation method. CMV was detected in 23 (56.1%) of 41 specimens by the development of cytopathic effect within 14 days.

Evaluation of a direct fluorescein-conjugated monoclonal antibody for detection of cytomegalovirus in centrifugation culture

A fluorescein-conjugated murine monoclonal antibody (MAb) reactive with cytomegalovirus (CMV) was evaluated for the detection of CMV in centrifugation culture. Of 188 specimens, 90 were positive for CMV in centrifugation culture. The fluorescein-conjugated MAb detected CMV in 86 of 90 (95%) specimens at 16 h postinoculation, and 88 of 90 (98%) were positive at 36 h. The fluorescein-conjugated MAb can be used in a direct immunofluorescence assay that can be completed in 15 min following cover slip fixation. Use of this antibody in centrifugation culture provides a convenient and rapid assay for the identification of CMV.