Infection of human retinal pigment epithelial cells with influenza A viruses.

Purpose: Ocular involvement in influenza A virus diseases is common but usually limited to mild conjunctivitis. Rarely, inflammation of the choriocapillaris may result in atrophia of the retinal pigment epithelium (RPE). Primary human retinal pigment epithelial (RPE) cells were infected with seasonal (H1N1 A/New Caledonia/20/99, H3N2 A/California/7/2004) or highly pathogenic avian H5N1 (A/Thailand/1(Kan-1)/04, A/Vietnam/1203/04, A/Vietnam/1194/04) influenza strains.

Methods: Influenza A virus replication was studied by investigation of cytopathogenic effects, immune staining for influenza A virus nucleoprotein, determination of virus titers, and electron microscopy. Apoptosis induction was examined by immune staining for activated caspase 3 and cleaved PARP. Proinflammatory gene expression was investigated by quantitative PCR.

Results: H5N1 but not seasonal influenza strains replicated to high titers (>10(8) TCID(50)/mL; 50% tissue culture infectious dose/milliliter) in RPE cells. H5N1 infection resulted in RPE cell apoptosis that was abolished by the antiviral drug ribavirin. Pretreatment with type I interferons (interferon-alpha and -beta) or the type II interferon, (interferon-gamma), inhibited H5N1 replication. Moreover, H5N1 infection induced expression of proinflammatory genes (tumor necrosis factor-alpha, CXCL8, CXCL10, CXCL11, and interleukin-6), which was inhibited by ribavirin in a concentration-dependent manner.

Conclusions: A novel cell type derived from the central nervous system was permissive to H5N1 influenza virus replication. This findings supports those suggesting H5N1 influenza strains to own a greater potential to spread to nonrespiratory tissues than seasonal human influenza viruses. Moreover, the data warrant the further study of the role of influenza A virus replication in retinal diseases associated with influenza A virus infections.