Characteristics of GFP-hMPV infection in BALB/c and SCID mice
Objective To compare the characteristics of hMPV infection in BALB/c and SCID mice.Methods BALB/c and SCID mice were infected intranasally with GFP-rhMPV,and sacrificed on day 3,5,7,9 and 14 post inoculation.Heart,liver,spleen,lungs,kidneys and brain of the animals were used for viral isolation,titration,pulmonary histopathology and detection of GFP-hMPV mRNA expression by RT-PCR and real-time PCR.Results Live viruses were successfully isolated from the lungs of infected mice.Viral titers peaked on the 5th day post inoculation.Viruses remained to be detectable on the 14th day post inoculation in SCID mice,but not in BALB/c mice,whereas genomic RNA of GFP-rhMPV was detectable by PCR targeting F gene in infected BALB/c mice.Live viruses were not able to be isolated from heart,liver,spleen,kidney and brain,neither was genomic RNA of hMPV able to be detected on the 5 th day post inoculation by RT-PCR and real-time PCR.Histopathology of lungs was characterized by interstitial pneumonia on 5 days post inoculation.Lung pathology score of BALB/c mice group was slightly lower than SCID,and the difference was not statistically significant.Conclusion GFP-rhMPV can only replicate in the immunocompetent and immunodeficient mouse lungs,but not in other organs.As compared to that in BALB/c mice,the viral replication appears to be more efficiently and for longer time in SCID mouse lungs probably due to the absence of host cellular and humaral immunity,but this does not necessarily result in more severe pathological lesion. 
 
Key words: 
Human metapneumovirus ;  BALB/c mice ;  SCID mice ;  Titer;  Pathology