Lung and lymph node explants to study the interaction between host cells and canine distemper virus.

Canine distemper virus (CDV, family Paramyxoviridae) is a widely known fatal disease in unvaccinated dogs and wild carnivores. The virus enters via the respiratory tract and rapidly spreads to the lymphoid organs. To investigate viral entry into these tissues, a dog tissue explant model was developed for lung and lymph nodes. Canine lung explants were cultured with CDV for three days. During this time CDV antigens were visible on alveolar cells, which were CD163-positive and SLAM-positive (signaling lymphocytic activation molecule), demonstrating that they were macrophages. The lymph node explants were maintained for five days. During this time the viral replication increased progressively by each day post infection and syncytia were observed by day three, post exposure. The microscopic distribution of CDV-positive cells in the lymph nodes, including the syncytia, and co-expression of CD163 and SLAM, demonstrated that they were macrophages. These findings suggest that alveolar macrophages are the first cells in the lung to become infected during CDV infection, and lymph node explants showed similar replication rates and virus-cell interactions as seen in experimental live animals. This demonstrates the utility of canine respiratory and lymphoid explant model to evaluate cell entry and viral replication of CDV and other morbilliviruses in dogs or other susceptible carnivores.