African green monkey kidney cells, commonly known as Vero cells, are a lineage of cells widely used in cell cultures. These cells, isolated from the kidney epithelial cells of an African green monkey (Chlorocebus sp.), have become indispensable tools in various fields of biological research, vaccine development, and diagnostic testing.
Characteristics of Vero Cells
The Vero cell lineage exhibits several key characteristics that make it suitable for various applications:
- Continuous and Aneuploid: Vero cells are a continuous cell line, meaning they can divide indefinitely under appropriate conditions. They are also aneuploid, possessing an abnormal number of chromosomes.
- Interferon-Deficient: Unlike normal mammalian cells, Vero cells do not secrete interferon alpha or beta when infected by viruses. However, they retain the Interferon-alpha/beta receptor, allowing them to respond to recombinant interferon added to their culture media.
Applications of Vero Cells
Vero cells are utilized in a wide array of applications, including:
1. Virus Amplification and Vaccine Development
Vero cells are commonly used as host cells for growing viruses. This is essential for:
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- Measuring viral replication in the presence or absence of research pharmaceuticals.
- Testing for the presence of viruses like the rabies virus.
- Growing viral stocks for research purposes.
The preparation of live, attenuated human influenza virus vaccines and large quantities of inactivated vaccines often requires an alternative host cell system. Embryonated chicken eggs may be insufficient and suboptimal for this purpose. Vero cells have been identified as a suitable system for the primary isolation and cultivation of influenza A and B viruses. Electron microscopic and immunofluorescence studies have confirmed that infected Vero cells undergo the same morphological changes as other polarized epithelial cells.
2. Cell Authentication
Tools for authenticating cell lines are critical for quality control in cell-based biological experiments. Short tandem repeat (STR) markers are used for human cell line authentication, and these methods can be expanded to nonhuman cell lines based on genome availability. A multiplex assay containing eight human STR markers has been developed to successfully genotype vervet genomic DNA samples from monkeys and commonly used vervet cell lines. The multiplex assay shows specificity for vervet DNA within the determined allele range for vervet monkeys.
The STR markers showed genetic stability in over sixty-nine passages of Vero cells, suggesting low mutation rates in the targeted STR sequences in the Vero cell line.
3. Cytotoxicity Assays
Vero cells are also used in cytotoxicity assays to assess the toxic effects of various substances on cells.
Variants of Vero Cells
Several variants of the Vero cell line exist, each with slightly different characteristics:
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- Vero 76 (ATCC No. CRL-1587): Isolated from Vero in 1968, it grows to a lower saturation density compared to the original Vero cells.
- Vero E6 / Vero C1008 (ATCC No. CRL-1586): A clone derived from Vero 76.
- Vero F6: A cell line transfected with the gene encoding HHV-1 entry protein glycoprotein-H (gH), with expression of gH under the control of the promoter region of gD.
Vero Cells and Influenza Virus Research
Preliminary studies indicated that an African green monkey kidney cell line (Vero) is a suitable system for the primary isolation and cultivation of influenza A viruses. Vero cells are suitable for isolation and productive replication of influenza B viruses. The biological and genetic properties of both influenza A and B viruses in Vero cells have been determined, and the receptors on Vero cells have been characterized in comparison to those on Madin-Darby canine kidney (MDCK) cells.
Sequence analysis indicated that the hemagglutinin of Vero cell-derived influenza B viruses was identical to that of MDCK-grown counterparts but differed from that of egg-grown viruses at amino acid positions 196 to 198. Fluorescence-activated cell sorting analysis showed that although Vero cells possess predominantly alpha2,3 galactose-linked sialic acid, they are fully susceptible to infection with either human influenza A or B viruses. Moreover, all virus-specific polypeptides were synthesized in the same proportions in Vero cells as in MDCK cells.
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Cell Authentication Using STR Markers
A functional vervet multiplex assay consisting of eight human STR markers with heterozygosity values ranging from 0.53-0.79 was successful in uniquely identifying sixty-two vervet monkey samples. The probability of a random match using these eight markers between any two vervet samples is approximately 1 in 1.9 million.
Table: STR Markers and Heterozygosity Values
| STR Marker | Heterozygosity Value |
|---|---|
| D17S1304 | >0.50 |
| D5S1467 | >0.50 |
| D19S245 | >0.50 |
| D1S518 | >0.50 |
| D8S1106 | >0.50 |
| D4S2408 | >0.50 |
| D6S1017 | >0.50 |
| DYS389 | >0.50 |
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CV-1 Cell Line
The CV-1 cell line was initiated in March of 1964 with a tissue section excised from the kidney of an adult male African green monkey (Cercopithecus aethiops). The fibroblast line was originally utilized in research focusing on the transformation of the cancer-causing Rous sarcoma virus (RSV), but now is popular as a host for acquired immunodeficiency disease (AIDS) research, as well as transfection experiments with simian virus 40 (SV40) and recombinant plasmid vectors. CV-1 cells exhibit fibroblast morphology, grow adherently to glass or plastic surfaces, and are negative for reverse transcriptase. The cells are known to be susceptible to several viruses, including poliovirus 1, herpes simplex, simian virus 40, California encephalitis, and both Eastern and Western equine encephalitis.
