MERS coronaviruses from camels in Africa exhibit region-dependent genetic diversity

Chu, Daniel K. W.; Hui, Kenrie P. Y.; Perera, Ranawaka A. P. M.; Miguel, Eve; Niemeyer, Daniela; Zhao, Jincun; Channappanavar, Rudragouda; Dudas, Gytis; Oladipo, Jamiu O.; Traoré, Amadou; Fassi-Fihri, Ouafaa; Ali, Abraham; Demissié, Getnet F.; Muth, Doreen; Chan, Michael C. W.; Nicholls, John M.; Meyerholz, David K.; Kuranga, Sulyman A.; Mamo, Gezahegne; Zhou, Ziqi; So, Ray T. Y.; Hemida, Maged G.; Webby, Richard J.; Roger, Francois; Rambaut, Andrew; Poon, Leo L. M.; Perlman, Stanley; Drosten, Christian; Chevalier, Veronique; Peiris, Malik

Because BF785 and Nig1657 differ from EMC and AH13 in having deletions in the ORF4b gene, and because the ORF4b gene product is reportedly associated with evasion of host cell IFN defense mechanisms (10, 11) , we further investigated whether the impaired replication competence correlated with a loss of such immune evasion in Calu-3 cells. In contrast to influenza H5N1, which was a potent inducer of IFN-β, IFN-λ1, IP10, ISG15, and Mx1 by 24 h post infection, the four MERS-CoV had little effect in up-regulating these innate immune responses at 24 h post infection, suggesting that potent innate immune-evasion mechanisms remained active in all four coronaviruses despite the ORF4b deletion in BF785 and Nig1657 viruses (Fig. 3) . Coronaviruses have multiple antagonists of IFN induction and signaling, and thus deletion of ORF4b by itself may not be decisive in this regard. By 48 h post infection, there was detectable induction of innate immune responses by some MERS-CoV, although this was still much lower than those elicited by H5N1 virus. Nig1657 also has deletions in ORF3. No consistent pattern was discerned between innate immune responses (or evasion of such responses) and the impaired virus replication competence of BF785 and Nig1657. Taking these findings together, we conclude that the impaired replication phenotype was not associated with the lack of innate immune evasion. In contrast, it was recently reported that a recombinant MERS-CoV clone with ORF3/4/5 deletions had reduced virus replication competence in Calu-3 (but not Vero) cells and in the lungs of human DPP4-transgenic mice, suggesting that the combined loss of these ORFs does lead to attenuation of the virus (18) .