These cells are derived in the dim dark ages from African green monkey kidney (Cercopithecus aethiops). After infection, these monkey cells were shown to make more MERS-CoV RNA than any other cell line tested and the second greatest quantity of viral particles (after goat cells).
Check out Eckerle et al. over at the CDC's Emerging Infectious Diseases journal for a very nice graphic.
This may be an artefact of the adapted cell-line....but let's not forget to test those baboons hmm?
