Replication of influenza A viruses in an avian macrophage cell line.

The virulent avian influenza virus A/Ty/Ont/7732/66 (H5N9) (Ty/Ont) causes severe destruction of the lymphoid cells in infected birds. Previous studies have suggested that viral infection of macrophages may be involved. However, Ty/Ont failed to replicate productively in primary cultures of chicken macrophages. Therefore, in an effort to develop an in vitro system for our studies, we examined the susceptibility of an avian macrophage cell line, HD11, to Ty/Ont. We found that Ty/Ont replicated in the HD11 cells to high titres, as measured by haemagglutination (HA) assays and infectivity yields. To determine whether this property was unique to Ty/Ont, we also examined the replication of influenza viruses representative of all 13 HA subtypes and an attenuated variant of Ty/Ont. All of the tested viruses replicated in HD11 cells; the avirulent strains required the presence of trypsin in the culture medium whereas virulent viruses and the attenuated variant of Ty/Ont did not. These results suggest that the HD11 cells can support the replication of a wide variety of influenza viruses and that this continuous avian cell line may prove useful for in vitro studies on these viruses.