Wild-type and innate immune-deficient mice are not susceptible to the Middle East respiratory syndrome coronavirus

Abstract

The Middle East respiratory syndrome coronavirus (MERS-CoV) is a newly emerging highly pathogenic virus causing almost 50 % lethality in infected individuals. The development of a small-animal model is critical for the understanding of this virus and to aid in development of countermeasures against MERS-CoV. We found that BALB/c, 129/SvEv and 129/SvEv STAT1 knockout mice are not permissive to MERS-CoV infection. The lack of infection may be due to the low level of mRNA and protein for the MERS-CoV receptor, dipeptidyl peptidase 4 (DPP4), in the lungs of mice. The low level of DPP4 in the lungs likely contributes to the lack of viral replication in these mouse models and suggests that a transgenic mouse model expressing DPP4 to higher levels is necessary to create a mouse model for MERS-CoV.

Fig. 1.

MERS-CoV pathogenesis in mice. Weight-loss curves of BALB/c (a), 129Sv/Ev (b) or 129/STAT1−/− mice (c) after either mock infection with PBS or MERS-CoV at two inoculum doses. (d, e) Lung homogenate from infected mice in (a–c) was assayed for the presence of virus at multiple time points after infection. Dotted line notes the level of detection in our TCID₅₀ assays. RNA was extracted from mouse lungs during infection and assayed for amount of viral RNA present during infection by real-time PCR analysis of the envelope ORF (f, g) or 1B(h, i). RNA from BALB/c mice (f, h) and RNA from 129Sv/Ev and 129/STAT1−/− mice (g, i) were assayed. Three mice at each time point and condition were used for each averaged value. Primers specific to the leader primer of MERS-CoV were used for real-time PCR analysis to identify subgenomic RNA as a reporter of viral replication (j, k). *P-value >0.5, P-value <0.5.

Fig. 2.

Histological analysis of MERS-CoV infected mice. (a) Histology of H&E stained lungs of BALB/c mice infected with MERS-CoV at 2 and 4 days p.i. (b) Histology of H&E stained lungs of 128/SvEv and 129/STAT1−/− mice infected with MERS-CoV at 9 days p.i.

Fig. 3.

DPP4 expression levels in mice. IHC staining of BALB/c mouse intestines (a) and lung (b) was performed with anti-DPP4 antibody at 1/100 dilution using antigen retrieval. We find significant levels of DPP4 protein expression in mouse intestines compared to secondary only control tissue; however, in mouse lungs we observe minimal DPP4 staining in airways or alveolar cells. (c) Real-time PCR analysis of DPP4 mRNA from intestines and lungs of mice compared to actin mRNA levels as a control.