Evaluation of human intestinal epithelial differentiated cells (Caco-2) for replication, plaque formation and isolation of avian influenza viruses

Although various cultured cells are used for propagating influenza A viruses, the types of cells which can support replication of and plaque production by low pathogenic avian influenza (LPAI) viruses without supplementary trypsin are limited. In this study, the infectivity and growth kinetics of as well as plaque production by LPAI viruses in Caco-2 cells were investigated. The suitability of this cell line for virus isolation was examined and compared with virus isolation in embryonated chicken eggs. Generation of Caco-2 mediated viral variants, if any, was assessed phenotypically and genotypically. It was found that Caco-2 cells can readily support continued replication of LPAI viruses without supplementary trypsin. Viruses replicate to high titer compared to embryonated chicken eggs, and more efficiently than in MDCK cells, without trypsin. Also, LPAI viruses produced plaques in Caco-2 cells. However, these cells were found to be less sensitive than embryonated chicken eggs for virus isolation. Notably, no phenotypic and genotypic changes of the viruses were observed during viral passages (at least up to 10th passage) in Caco-2 cells. These findings indicate that Caco-2 cells may provide an appropriate substrate for studying and cultivating AIVs.