Rapid detection of cytomegalovirus in clinical specimens by immunofluorescent staining of shell vial cultures

Direct quantitative comparison of shell vial and conventional culture for detection of CMV viremia

BACKGROUND

Centrifugation shell vial (SV) and conventional tube culture (TC) are the most common methods for detecting cytomegalovirus (CMV) viremia. Studies have indicated that SV is more sensitive than TC but at least one report suggested that TC was more sensitive. Because CMV in the blood is primarily associated with infected leukocytes, the number of leukocytes inoculated into the different culture systems could affect the sensitivities of the two systems.

OBJECTIVES

To compare the sensitivities of SV and TC for detection of CMV viremia by inoculating equal numbers of leukocytes into paired SV cultures and TC cultures.

STUDY DESIGN

Leukocytes from transplant recipients were isolated and counted. Equal numbers of leukocytes were then inoculated into each of two MRC-5 SV and into each of two MRC-5 TC. SV was considered positive when either one or both vials were positive, and TC was considered positive when either one or both tubes showed evidence of CMV cytopathic effect (CPE).

RESULTS

From a total of 434 specimens tested, 85 (19.6%) were positive by SV or TC. CMV was detected by SV in 75 (88%) of the positive specimens, compared to TC which was positive in 40 (47%) of the positive specimens.

CONCLUSIONS

When equal numbers of leukocytes were inoculated into each system, SV had significantly greater sensitivity than TC for detecting CMV viremia. However, a small number of episodes of viremia were detected only by TC. Therefore, both methods should be used for maximum sensitivity.

Cytomegalovirus DNA polymerase activity and an 80 kDa-associated polypeptide: a potential diagnostic tool for CMV disease

CMV has been reported to be associated with a DNA polymerase activity (DPA). In this communication its purification, characterization and potential diagnostic value were examined. CMV DNA polymerase was prepared from cell free supernatants of CMV (AD 169) infected cultures. Separation and purification of the enzyme was accomplished by column chromatography of the purified, lysed virus. CMV DPA was measured on an oligo (dT)-poly (dA) template primer. SDS-PAGE and western blot analysis under reducing conditions using an anti-CMV early antibody showed an 80 kDa protein band that was associated with the peak of polymerase activity. However, CMV isolates and CMV from urines from CMV retinitis patients immunoblotted by the same Ab revealed 140 kDa and 80 kDa bands under non-reducing and reducing conditions respectively, the latter was also associated with a 58 kDa band. The diagnostic value of the CMV associated DAP was tested using CMV positive urines. The latter demonstrated high PAA-sensitive DPA activity, compared to normal, HSV positive urines and urines from HBSAg positive patients. Taken collectively, these findings indicate the potential usefulness of CMV-associated DNA polymerase activity in the diagnosis and follow-up of patients with CMV-related illnesses.

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.

A microneutralization enzyme immunoassay for antibody to human cytomegalovirus

We have developed a relatively rapid, sensitive and quantitative microneutralization assay for antibody to human cytomegalovirus (HCMV). Cell monolayers in 96-well microtiter plates inoculated with pre-incubated virus-antibody mixtures were fixed after 3 days. Infectious foci were stained with peroxidase-labeled human monoclonal antibody to a 64 kDa immediate early antigen of HCMV, and the plates were read at OD450. The 50% neutralization titer of the antibody was calculated. A study with 20 human sera and a human monoclonal antibody which neutralizes virus showed that this microneutralization enzyme immunoassay is more sensitive than, and as quantitative as, the conventional plaque reduction assay for antibody to HCMV. The neutralizing antibody titers of each sample measured by these two methods showed good correlation (n = 19, r = 0.884). Thus, this new assay is a useful and valid alternative to the conventional method for mass screening of sera and hybridoma fluids, and considerably more rapid.

Improved detection of cytomegalovirus viremia in AIDS patients using shell vial and indirect immunoperoxidase methodologies

One hundred twelve peripheral blood specimens were tested for the presence of cytomegalovirus (CMV) by the tube culture indirect immunoperoxidase (TC-IPA) procedure, the shell vial assay [shell vials were pre- and postinoculation treated with medium containing 2 of 10% fetal bovine serum (FBS) or 100 micrograms% cortisol] (SV-IFA), and conventional (MRC-5) tube cultures (TC-CPE). CMV was detected in 25 (22%) of the 112 specimens tested by at least one of these methods. The detection/isolation of CMV among the 25 positive specimens in shell vials maintained with 2% FBS, 100 micrograms% cortisol + 2% FBS, and 10% FBS was 36, 44, and 52%, respectively. Detection/isolation of the virus from blood by TC-IPA and TC-CPE was 52% and 76%, respectively. A significantly greater CMV detection rate occurred using TC-CPE compared to SV-IFA treated with medium supplemented with an FBS concentration of 2% (P = .0132), but not medium containing the higher serum supplement or the glucocorticoid (P greater than .05). Differences in the identification of a CMV viremia were observed by IPA, SV-IFA, and TC-CPE methodologies on a patient-to-patient basis, denoting the necessity of incorporating each methodology into the CMV screening panel. Demographic analysis of 82 AIDS patients showed a CMV viremia prevalence of 9% (2/28) in intravenous drug users, 57% (27/47) in homosexual patients, and 22% (2/9) in heterosexual and transfusion patients. Overnight (24 hr) storage of whole blood at 4 or 24 degrees C, respectively, reduced CMV recovery by 40% and 65%, when tested by TC-CPE.(ABSTRACT TRUNCATED AT 250 WORDS)

Cytomegalovirus DNA in the sera of patients with cytomegalovirus pneumonia

We attempted to detect cytomegalovirus DNA (CMV-DNA) in the sera of four leukaemia patients who underwent an allogeneic bone marrow transplant (BMT), in six leukaemia patients who suffered from pneumonia and in 16 healthy subjects, using the polymerase chain reaction (PCR). Three of the four BMT patients subsequently developed CMV pneumonia. In two cases, CMV-DNA was detected in the sera at about the time the pneumonia occurred, and the amount of DNA increased with disease progression. The serum of the third patient became positive for CMV-DNA before he developed pneumonia. The fourth patient did not develop CMV pneumonia, but his urine became persistently positive for CMV-DNA soon after the BMT, whereas the serum was negative. A relationship was found between the occurrence of pneumonia and the serum level of CMV-DNA. CMV-DNA was also detected in three of six pneumonia patients whose anti-CMV IgM antibodies were elevated in the circulation. Sera from the 16 normal subjects were negative for CMV-DNA, regardless of their being seropositive or seronegative for CMV. While it had been previously thought that CMV did not exist in serum, we detected CMV-DNA in serum by PCR in the active disease stage. Our results suggest that PCR would be useful for the early diagnosis of CMV pneumonia and in monitoring its course.

Identification of cytomegalovirus infection in acquired immunodeficiency syndrome

Cytomegalovirus (CMV) infection was observed in 10 of 12 autopsy cases of acquired immunodeficiency syndrome (AIDS) and appears to be the commonest life-threatening viral infection in AIDS. In all 10 cases, adrenal glands were affected with CMV and adrenal medullary necrosis was present in 6 cases. Lungs were affected with CMV in 7 cases with disseminated infection and positive CMV culture. In situ hybridization of tissue sections with CMV-specific DNA provided positive staining for CMV in inclusions as well as other infected cells without obvious inclusions. Human diploid lung fibroblasts were infected with isolated CMV in culture, yielding positive CMV identification within 5 days by in situ hybridization before specific cytopathic changes appeared in the fibroblasts. The early and specific detection of CMV is possible by in situ hybridization with cultured fibroblasts.

Effect of age of shell vial monolayers on detection of cytomegalovirus from urine specimens

The effect of age of MRC-5 cell monolayers in shell vials on the detection of cytomegalovirus (CMV) from urine was evaluated. When the AD169 strain of CMV was used, 8-day-old monolayers had a higher mean count of fluorescent foci than 15-day-old monolayers did (5.78 versus 2.86) (P less than 0.02) and were more frequently positive (21 of 23 shell vials versus 14 of 22 shell vials) (P less than 0.04). Commercial shell vials used for clinical specimens were evaluated in groups of 8- to 11-, 12- to 15-, and 8- to 15-day-old monolayers. When compared with laboratory-prepared shell vials ranging in age from 3 to 9 days, commercial shell vials had a lower number of fluorescent foci in all groups (P less than 0.03, P less than 0.0001, and P less than 0.0001, respectively), the 12- to 15- and 8- to 15-day-old groups were less frequently positive (P less than or equal to 0.02 and P less than 0.02, respectively), and all three groups were more susceptible to the toxic effects of urine (P less than 0.0001, P less than 0.01, and P less than 0.0001, respectively). For all 191 specimens cultured (8- to 15-day-old group), one or both monolayers were destroyed in 60 (31.4%) specimens compared with 9 (4.7%) specimens toxic to laboratory-prepared shell vials (P less than 0.0001). Both the decreased sensitivity of older MRC-5 cells and the increased sensitivity to the toxic effects of urine made commercial shell vial less sensitive than laboratory-prepared shell vials for the detection of CMV.

Multisite evaluation of a monoclonal antibody reagent (Syva) for rapid diagnosis of cytomegalovirus in the shell vial assay

A pre-cytopathic effect (CPE) monoclonal antibody reagent (Syva Co., Palo Alto, Calif.) was evaluated in four laboratories for the rapid detection of cytomegalovirus (CMV) in shell vial cell cultures at 16 to 24 h and 40 to 48 h postinoculation. Results were compared with those obtained by inoculation of the specimen into conventional tube cell cultures that were examined for the presence of typical CMV CPE and subsequently tested by reaction with the monoclonal antibody reagent in an indirect immunofluorescence test. Of 937 specimens, CMV was positive in 184 (20%). CMV was detected twice as frequently in shell vials only (n = 29) as in conventional tube cell cultures (n = 14). Pre-CPE shell vial assay was 91% sensitive (range, 84 to 98%) and 96% specific (range, 93 to 98%) compared with the detection of CPE in conventional tube cell cultures. Overall, 137 of 166 (83%) and 143 of 166 (86%) of the CMV strains were detected at 16 to 24 h and 40 to 48 h postinoculation, respectively. The Syva reagent produced sensitive and specific results for the rapid detection of CMV infection in shell vial cell cultures and reliably confirmed the presence of the virus as detected by CPE in conventional tube cell cultures.

Clinical experience with cytomegalovirus isolation using conventional cell cultures and early antigen detection in centrifugation-enhanced shell vial cultures

A total of 1,915 clinical samples was inoculated by low-speed centrifugation into shell vials (Bartels Immunodiagnostics, Bellvue, Wash.) containing cover slip monolayers of MRC-5 fibroblasts. At 1 and 2 days postinoculation, one cover slip was stained by an indirect immunofluorescence technique using a monoclonal antibody (Biotech Research Laboratories for Dupont, Billerica, Mass.) to cytomegalovirus (CMV) early antigen (EA). Clinical samples were also inoculated into three MRC-5 or MRHF cell cultures which were observed for 30 days for the appearance of a cytopathic effect (CPE). Of 157 CMV-positive samples, 92 (59%) were identified by centrifugation-enhanced EA (CE-EA) and 131 (83%) produced a CPE. CE-EA was less sensitive than CPE for all types of samples, although 17% of CMV-positive samples were detected by CE-EA alone. Evaluation of the CMV status of patients with CE-EA-positive-CPE-negative samples indicated that these samples likely represented true CMV-positive results. The average elapsed time between culture inoculation and identification of CMV decreased as follows when both CE-EA and CPE, rather than CPE alone, were used: urines, 15 to 7 days; buffy coats, 18 to 9 days; lung samples, 13 to 8 days; throat samples, 18 to 7 days. Although CE-EA was less sensitive than 30-day cell culture, both CE-EA and CPE were identified as valuable in CMV detection, and neither could be discontinued without a decrease in the CMV isolation rate or an increase in the turnaround time.