The title of this post should not come as a surprise to readers of virology blog – it was shown in 1974 that zinc could interfere with replication of rhinoviruses (see “Zinc and the common cold“). I am referring to the result of my first experiment to study the mechanism of zinc inhibition – something I promised I would document on these pages.
I am interested in understanding how zinc inhibits rhinovirus replication. Answering this question could lead to new ways to prevent common colds caused by these viruses. The first step was to reproduce the effect of zinc in my laboratory with my stocks of rhinovirus. I selected rhinovirus type 1a for my initial experiments because we’ve worked with this serotype in the past: we know the genome sequence and how the virus behaves in a mouse model. I started by doing a plaque assay with and without zinc in the medium. I prepared tenfold dilutions of virus and inoculated separate monolayers of HeLa cells with 2000, 200, and 20 plaque forming units. After allowing the virus to attach to cells for 45 minutes, I added an agar overlay to the cells with or without zinc chloride (ZnCl2). I selected 0.1 millimolar ZnCl2 because that is the concentration which had been reported to effectively inhibit plaque formation by rhinovirus type 1a. The plates were incubated for four days at 32°C and then stained. The results are shown in the photo. Plaque assays are typically done in duplicate but for simplicity only one plate of each dilution is shown.
Twenty plaques were observed on the highest dilution of virus plated in the absence of ZnCl2. Ten-fold lower dilutions produced increases in plaque number, although the plaques are too numerous to count. In the presence of ZnCl2, no plaques were observed on cells inoculated with 20 PFU. A few plaques are observed on the intermediate dilution and many more on the lowest dilution. Plaques observed in the presence of ZnCl2 are smaller than those observed in the absence of the metal.
What do you think is going on here, and what should I do next? If you’ve kept up with virology 101 you have all the tools to answer these questions. Please post your thoughts in the comments section.
KORANT, B., KAUER, J., & BUTTERWORTH, B. (1974). Zinc ions inhibit replication of rhinoviruses Nature, 248 (5449), 588-590 DOI: 10.1038/248588a0