Microculture Plaque Neutralization Test for California Group Arboviruses

A microculture plaque neutralization test is described for California-group arboviruses that is as precise and quantitative as the standard test conducted in 60-mm petri dishes. It was shown that there was no significant between-panel or between-day variation in determinations and that a single pipette could be used for all serum-dilution levels within a titration without inoculum carry-over effect. The experimental protocol and statistical methods used produce 50% neutralization end points that meet the assumptions of parametric statistics. This permits the power and versatility of the analysis of variance to be exploited in testing for treatment effects in serological and immunological studies with viruses.     

Plaque Assay for Murine Norovirus

Murine norovirus (MNV) is the only member of the Norovirus genus that efficiently grows in tissue culture ^{1, 2}. Cell lysis and cytopathic effect (CPE) are observed during MNV-1 infection of murine dendritic cells or macrophages ¹. This property of MNV-1 can be used to quantify the number of infectious particles in a given sample by performing a plaque assay ¹. The plaque assay relies on the ability of MNV-1 to lyse cells and to form holes in a confluent cell monolayer, which are called plaques ³.Multiple techniques can be used to detect viral infections in tissue culture, harvested tissue, clinical, and environmental samples, but not all measure the number of infectious particles (e.g. qRT-PCR). One way to quantify infectious viral particles is to perform a plaque assay ³, which will be described in detail below. A variation on the MNV plaque assay is the fluorescent focus assay, where MNV antigen is immunostained in cell monolayers ⁴. This assay can be faster, since viral antigen expression precedes plaque formation. It is also useful for titrating viruses unable to form plaques. However, the fluorescent focus assay requires additional resources beyond those of the plaque assay, such as antibodies and a microscope to count focus-forming units. Infectious MNV can also be quantified by determining the 50% Tissue Culture Infective Dose (TCID₅₀) ³. This assay measures the amount of virus required to produce CPE in 50% of inoculated tissue culture cells by endpoint titration ⁵. However, its limit of detection is higher compared to a plaque assay ⁴.In this article, we describe a plaque assay protocol that can be used to effectively determine the number of infectious MNV particles present in biological or environmental samples ^{1, 4, 6}. This method is based on the preparation of 10-fold serial dilutions of MNV-containing samples, which are used to inoculate a monolayer of permissive cells (RAW 264.7 murine macrophage cells). Virus is allowed to attach to the cell monolayer for a given period of time and then aspirated before covering cells with a mixture of agarose and cell culture media. The agar enables the spread of viral progeny to neighboring cells while limiting spread to distantly located cells. Consequently, infected cells are lysed and form holes in the monolayer known as plaques. Upon sufficient spread of virus, plaques become visible following staining of cells with dyes, like neutral red, methylene blue, or crystal violet. At low dilutions, each plaque originates from one infectious viral particle and its progeny, which spread to neighboring cells. Thus, counting the number of plaques allows one to calculate plaque-forming units (PFU) present in the undiluted sample ³.     

Rapid Plaque Assay for Encephalomyocarditis Virus

A liquid overlay plaquing technique is described which offers a rapid and simple plaque assay system for small plaque variants of encephalomyocarditis virus.     

Microtissue Culture Plaque Assay for Herpesvirus saimiri

A microtissue culture method for the plaque assay of Herpesvirus saimiri has been developed. Virus titrations carried out in Microtest II tissue culture plates (Falcon) yielded reproducible results that agreed well with those obtained by employing macrocultures. The described method is quantitative, reproducible, economical, and suitable for routine assay of large numbers of virus samples.     

A Plaque Method for Rubella Virus Assay

A method has been described in which suitable dilutions of rubella virus will induce the formation, in a monolayer of green monkey kidney cells, of islets of infected cells which were protected from the effects of Echo 11 challenge virus. The number of islets or “negative” plaques was proportional to the dilution of rubella virus inoculated on to the monolayer. Using this method, it was observed that bentonite adsorption increased the plaque assay values of rubella virus pools. This suggested that rubella virus interference may be mediated by an interferon-like principle.     

Plaque Assay for Pneumonia Virus of Mice

A plaque assay for the quantitation of pneumonia virus of mice is described. To obtain reproducible plaque formation, proteolytic enzymes had to be incorporated in the overlay medium. The plaque morphology observed in the presence of pancreatin and chymotrypsin was superior to that seen with trypsin. Although the plaque assay was found to be slightly less sensitive than the TCID(50) determination described by Harter and Choppin, it enables cloning of the virus by plaque selection and permits further study of pneumonia virus of mice.     

Double-Layer Plaque Assay for Quantification of Enteroviruses

We describe here a double-layer plaque assay for the quantification of enteroviruses, combining a monolayer plaque assay and a suspended-cell plaque assay. The double-layer assay provides significantly greater counts than other methods of virus quantification of both suspensions of pure culture viruses and naturally occurring viruses. The counts obtained by this method are approximately one order of magnitude greater than those obtained with the more commonly used method, the monolayer plaque assay. We conclude that the methods available for quantifying viruses rank in efficiency as follows: double-layer plaque assay ≥ suspended-cell plaque assay > counting cytopathogenic virus adsorbed to cellulose nitrate membrane filters ≥ most probable number of cytopathogenic units > monolayer plaque assay. Moreover, the double-layer plaque assay allows the use of two different cell lines in the two layers. Using the human colonic carcinoma cell line CaCo2 facilitates the recovery of a greater number and diversity of naturally occurring enteroviruses in water than the monolayer agar method. In addition, the pretreatment of cells with 5-iodo-2′-deoxyuridine (IDU) prior to the quantification of enteroviruses by the double-layer plaque assay provides significantly higher recoveries than the use of IDU does with the other methods of quantification.     

Plaque Assay for Q Fever and Scrub Typhus Rickettsiae

The plaque assay procedure developed for spotted fever and typhus group rickettsiae is also appropriate for scrub typhus and Q fever rickettsiae. The plaque titers of suspensions of Rickettsia tsutsugamushi and Coxiella burnetii compared favorably with end points obtained by titrations in mice.     

SARS-CoV细胞空斑试验

目的建立适用于生物安全三级实验室操作的SARS．CoV空斑试验方法。方法SARS－CoVl0倍系列稀释接种Vero－E6细胞,用0．6％琼脂糖覆盖中性红着色（琼脂糖．中性红法）或覆盖1％甲基纤维素,4％甲醛固定,结晶紫染色（甲基纤维素－结晶紫法）,空斑计数。结果琼脂糖－中性红法病毒滴度为6．14Lg pfu／mL,甲基纤维素－结晶紫法病毒滴度为6．57Lg pfu／mL。结论二种空斑试验方法相比,病毒滴度无明显差异。甲基纤维素－结晶紫空斑试验法形成的空斑比琼脂糖－中性红法清晰、操作简单安全、结果可长期保存。     

Plaque Assay System for Several Species of Rickettsia

The plaque assay developed in this laboratory for the Bitter Root strain of Rickettsia rickettsii has recently been shown to be appropriate for other rickettsiae.     

普通大气条件下的蚀斑试验

草鱼出血病病毒湖南邵阳株(CCHV—873),常规培养条件下能在鱼肾(CIK)细胞上形成直径约2mm的蚀斑。当采用三种缓冲系统(MFM-NaHCO_3、MEM-Tris、MEMHEPES)的培养液在普通大气条件下分别培养CIK细胞时,三天内培养液的pH略有变化,其变化范围在0.2—0.4左右,但细胞生长仍然良好,三者无明显差别。在上述系统,以双相法(培养液-凝胶)进行蚀斑试验时,观察到无机缓冲系统培养液的pH变化较大,有机缓冲系统则较稳定,且蚀斑形成的数量显著不同,后者效价比前者要高出4个数量级。因此,在培养液中加入适量的有机缓冲液代之以CO_2的调节是完全有可能的。     

Immunochemical Characterization of Plaque Mutants of Simian Virus 40

Analysis of large and small plaque mutants of simian virus 40 using antisera prepared against each has revealed quantitative and possibly qualitative antigenic differences for each plaque type. A sensitive micro radioisotope precipitation test permitted evaluation of immunochemical similarities and differences of capsid antigens by inhibition of precipitation.     

Evaluation of a Plaque Assay for the Maedi-Progressive Pneumonia-Visna Viruses

A simple and direct plaque assay for maedi virus, two strains of progressive pneumonia virus, and two strains of visna virus has been developed and evaluated. The technique allows the plaques formed by these viruses to be localized without disturbing the host-cell substrate of sheep choroid plexus cells or the gelled maintenance medium over the host-cell monolayer. Diethylaminoethyl-dextran supplementation of the medium used to overlay strain K796 visna virus-infected cultures decreases the time required for maximum plaque development from 12 to 10 days, enhances the contrast of the plaques, increases the titer of plaque-forming units, and permits a plaque size heterogeneity to be realized. Both large and small plaques occur in cultures infected with the visna viruses, one strain of progressive pneumonia virus, or maedi virus. In contrast, the plaques observed in cultures infected with the second strain of progressive pneumonia virus are relatively homogeneous in size.     

用蚀斑法滴定痘苗病毒的准确性及其精确数学模型的探讨

用蚀斑法滴定病毒是确定感染病毒颗粒存在数量的一种较准确方法。本实验表明,痘苗病毒吸附4h后仍有大量病毒粒子未能吸附到细胞单层,进而测定出病毒接种量、维持液加量和所测病毒滴度间具有一种互为消长的非线性相关性。因而设计了几种检测方法,其准确性均优于常规痘苗病毒蚀斑测定法。利用装配有Mathematic软件包的计算机在痘苗病毒接种量、维持液加量和所测病毒滴度间建立了曲线拟合模型和曲面拟合模型。通过曲线拟合模型推断病毒感染滴度为常规法滴定值的近5倍。     

Plaque Formation with Simian Virus 40: Enhancement by Dimethyl Sulfoxide

Dimethyl sulfoxide (DMSO) added to agar overlays during plaque assays of simian virus 40 (SV40) in CV1 monkey cells increases the plaque size and number and enables plaques to be read several days earlier than usual. DMSO appears to act during development of plaques, perhaps by causing cell lysis at smaller burst sizes in the presence of near-lethal DMSO concentrations. It does not act synergistically in determining virus inactivation with UV light and is equally effective on wild type and a late mutant of SV40.     

流行性出血热(EHF)病毒半微量甲基纤维素空斑法的建立

本文报道EHF病毒一种新的空斑形成按术,即半微量甲基纤维素空斑法的建立及其应用。6株来源不同的毒株均可在V_(ero)-E_6细胞或V_(ero)细胞上形成清晰的空斑,形成的空斑能被特异抗EHF病毒血清所中和。其敏感性与用琼脂糖作覆盖物的空斑法一致。该法具有操作简便、快速等优点,适用于EHF的病原学和血清学研究。     

油桐尺蠖核型多角体病毒的空斑测定

在油桐尺蠖卵巢细胞系上对油桐尺蠖核型多角体病毒(BsNPV)进行了空斑测定。用此方法测定了BsNPV的感染力,并将所得的结果与其TCID_(50)进行比较,结果显示这两种方法在测定病毒感染力时敏感性相似。     

Plaque Assay for Polyoma Virus on Primary Mouse Kidney Cell Cultures

A plaque assay for polyoma virus using primary baby mouse kidney cells is reported.     

Human Cytomegaloviruses Expressing Yellow Fluorescent Fusion Proteins - Characterization and Use in Antiviral Screening

Recombinant viruses labelled with fluorescent proteins are useful tools in molecular virology with multiple applications (e.g., studies on intracellular trafficking, protein localization, or gene activity). We generated by homologous recombination three recombinant cytomegaloviruses carrying the enhanced yellow fluorescent protein (EYFP) fused with the viral proteins IE-2, ppUL32 (pp150), and ppUL83 (pp65). In growth kinetics, the three viruses behaved all like wild type, even at low multiplicity of infection (MOI). The expression of all three fusion proteins was detected, and their respective localizations were the same as for the unmodified proteins in wild-type virus–infected cells. We established the in vivo measurement of fluorescence intensity and used the recombinant viruses to measure inhibition of viral replication by neutralizing antibodies or antiviral substances. The use of these viruses in a pilot screen based on fluorescence intensity and high-content analysis identified cellular kinase inhibitors that block viral replication. In summary, these viruses with individually EYFP-tagged proteins will be useful to study antiviral substances and the dynamics of viral infection in cell culture.