SARS- and MERS-CoV receptor expression and virus infection experiments in human primary cells. (A) SARS- and MERS-CoV receptor expression of human Angiotensin-converting-enzyme-2 (ACE-2) and Dipeptidyl-peptidase-4 (DPP-4), respectively, in cryosections of a healthy human kidney and (B) in primary bronchial (HBEpC) and renal (HREpC) epithelial cells. For positive controls, ACE2- and DPP-4-expressing primate cells (kidney cells from African green monkey [Vero E6]) were stained in parallel. Cell lines known to be negative for ACE-2 (kidney cells from Syrian hamster [BHK]) or DPP-4 (kidney cells from African green monkey [COS-7]) were used as negative controls. The white bar represents 50 μm. (C) Cell morphology and cytopathic effect (CPE) formation of human primary renal epithelial cells (HREpC) infected with MERS-CoV or SARS-CoV with 0.5 plaque-forming units of either virus per cell. A pronounced CPE formation 20 hours post infection (hpi) was seen only after infection with MERS-CoV in HREpC but not in cells infected with SARS-CoV. No CPE formation was seen in HBEpC infected with MERS-CoV or SARS-CoV (data not shown). Upper row: 100-fold magnification, lower row: 400-fold magnification, bright field microscopy (D) Replication of SARS- and MERS-CoV on HBEpC and HREpC determined by real time RT-PCR after 0, 20 and 40 hpi (E) Progeny virus measured by titration of supernatants in duplicates in a plaque assay in Vero cells. MERS-CoV replicates in HREpC with peak titers of 6.2 log plaque forming units (PFU)/mL, showing a 2,9-fold log difference between HREpC and HBEpC, while replication of SARS-CoV showed only a 1-fold log difference between bronchial and renal primary cells. Replication levels for each virus used are given as log of the genome equivalents (GEs) (D) or as plaque-forming units (PFUs) (E). All virus infection experiments were performed in triplicates. Bars represent mean values, error bars represent standard deviation of triplicates.
Eckerle et al. Virology Journal 2013 10:359 doi:10.1186/1743-422X-10-359