C6/36 cells are a widely utilized tool in scientific laboratories, particularly for studying insect-borne diseases. They provide a controlled environment for investigating how viruses interact with insect cells, contributing significantly to virology and the development of interventions against infectious diseases.
Origin and Basic Application
C6/36 cells originated from the Aedes albopictus, commonly known as the Asian tiger mosquito, specifically from larval tissues in 1967. A subclone, C6/36, was subsequently selected for its consistent production of high virus yields. This particular cell line is officially available through the American Type Culture Collection (ATCC).
These cells are widely used for propagating and studying various arboviruses, such as Zika, dengue, chikungunya, and West Nile viruses. Their ability to replicate these viruses to high titers, often reaching 107 to 108 plaque-forming units per milliliter (PFU/ml) for dengue virus, makes them valuable for laboratory work, including detection and analysis.
A stable insect cell line like C6/36 is highly advantageous for virological research because it provides a consistent and reproducible system for virus cultivation outside of a living organism. Researchers can grow large quantities of viruses for experiments, including studies on viral replication, pathogenesis, and the testing of antiviral compounds. Furthermore, these cells can be maintained under controlled laboratory conditions, which simplifies experimental design and reduces variability inherent in working with live mosquitoes.
Genetic and Antiviral Peculiarities
The genome of C6/36 cells is notably complex and exhibits a high degree of heterozygosity, meaning that for many genes, there are two distinct copies present. This genetic makeup suggests a divergence from the wild Aedes albopictus mosquito genome, indicating that the cell line has acquired unique characteristics over its many years in culture. The assembled C6/36 genome is also larger than expected compared to wild mosquito genomes.
A key characteristic of C6/36 cells is their impaired antiviral RNA interference (RNAi) pathway, a primary defense mechanism against viral infections in mosquitoes. This dysfunction is linked to a lack of proper Dicer-2 activity, a key enzyme involved in processing viral double-stranded RNA into small interfering RNAs (siRNAs). In healthy mosquito cells, Dicer-2 cleaves viral double-stranded RNA, which then guides the destruction of viral RNA.
However, in C6/36 cells, this process is altered; for instance, virus-derived small interfering RNAs (viRNAs) from West Nile virus (WNV) infected cells are primarily 17 nucleotides in length, while those from Sindbis virus (SINV) and La Crosse virus (LACV) infected cells are 26–27 nucleotides long. This suggests a defect in the canonical RNAi machinery, making these cells highly permissive to various arboviruses, allowing them to replicate to very high titers for laboratory amplification.
Despite their utility for virus replication, the dysfunctional RNAi pathway in C6/36 cells means they may not accurately represent how natural mosquito-arbovirus interactions occur. In wild mosquitoes, a robust RNAi response would typically limit viral replication and spread. The absence of this functional pathway can lead to an overestimation of viral replication efficiency.
Implications for Scientific Study
The unique characteristics of C6/36 cells, particularly their high permissiveness to arboviruses, offer significant advantages for certain types of scientific research. Their ability to support high viral titers makes them valuable for isolating viruses from clinical samples, propagating large quantities of virus for experimental use, and developing vaccine candidates. For instance, C6/36 cells are used to grow dengue viruses for vaccine preparation. This high yield simplifies the process of obtaining enough viral material for studies that require substantial amounts of virus.
However, these same peculiarities also introduce limitations and considerations for researchers. The dysfunctional RNAi pathway in C6/36 cells means they do not fully mimic the natural immune response of mosquitoes to viral infections. This can lead to a skewed understanding of host-virus interactions if findings from C6/36 cells are directly extrapolated to live mosquitoes. For example, while C6/36 cells are highly susceptible to infection, a mosquito in its natural environment would mount an RNAi defense that could suppress viral replication.
Beyond their antiviral response, C6/36 cells also display other physiological adaptations to laboratory culture conditions. They show a reduced expression of aquaporins and inward rectifier K+ channels, which are important for water balance and ion transport in live mosquitoes. These adaptations, while beneficial for cell survival in a stable laboratory environment, further differentiate them from cells within a living mosquito. Additionally, the C6/36 cell line can exhibit chromosomal abnormalities with increased passages, which may introduce genetic drift and affect experimental reproducibility over time.
Researchers account for these characteristics by using C6/36 cells for specific purposes, such as initial virus isolation and large-scale virus amplification. For studies focusing on the complete mosquito immune response or virus-vector interactions in a natural context, researchers often validate findings from C6/36 cells using other mosquito cell lines with intact antiviral pathways or through in vivo studies involving live mosquitoes. This approach ensures a more comprehensive understanding of the complex relationship between arboviruses and their mosquito hosts.