Female A/J and C57BL/6J mice, 6-8 weeks of age were purchased from Jackson laboratories. The mice were maintained in microisolator cages, housed in the animal facility at The Toronto Hospital Research Institute, University of Toronto, and fed standard lab chow diet and water ad libitum. All protocols were approved by the animal Welfare Committee. Parental virus Mouse Hepatitis Virus strain 1 (MHV1) was ordered from the American Type Culture Collection. As previously described (33) , MHV1 infection was carried out in a viral isolation room. A/J and C57BL/6J mice were anesthetized by intraperitoneal injection with 0.2 ml 10% pentobarbital diluted in normal saline. Mice were left untreated or received 5000 plaque forming unit (PFU) of MHV1 intranasally. Mice were sacrificed 12, 36 and 96 h postinfection and lung tissue was collected.