A model to study neurotropism and persistency of Japanese encephalitis virus infection in human neuroblastoma cells and leukocytes

Japanese encephalitis (JE) is the most common mosquito-borne encephalitis in the Asia-Pacific region. Patients with JE usually present neuronal involvement, but other organ involvement is relatively rare. Employing human neuroblast-derived (NB) cell lines and different blood cells (erythrocytes, lymphocytes, granulocytes and monocytes), the neurotropism and persistency of Japanese encephalitis virus (JEV) in human cells was investigated. It was found that JEV could not replicate in erythrocytes, granulocytes or lymphocytes. Monocytes and NB cell lines could support replication of JEV as demonstrated by expression of viral NS3 antigen and virus plaque-forming units (p.f.u.). JEV could replicate more efficiently in neuroblastoma (HTB-11) cells than in monocytes after infection for 48 h (2.1 ± 1.2 × 10⁷ vs 2.8 ± 0.7 × 10² p.f.u. ml^-1). Two different strains of JEV revealed a similar infectivity to different leukocytes and four NB cell lines. In a kinetic study, it was found that JEV-infected monocytes possessed a high viability (90%) after infection for 5 days, while JEV-infected neuroblastoma cells suffered cell apoptosis in 2 days and decreased viability to less than 1% in 5 days. Further studies showed that monocytes could take up JEV rapidly, displaying a log scale increase of intracellular JEV titres in 9 h after infection. Significantly, extracellular production of JEV by monocytes started in 12 h, peaked in 3 days and persisted for more than 3 weeks. These results suggest that JEV-infected monocytes may play an important role in harbouring JEV for eventual transmission to NB cells and that modulation of JEV-induced NB cell apoptosis may be useful in treating patients with JE.