To determine whether ATE cells support the replication of IBV, two egg-adapted Taiwan IBV strains, 2575/98 and 2296/95, were used in this study. These two IBV viruses cannot infect primary chicken embryonic fibroblast cells or immortalized DF1 chicken fibroblast cells. The ATE cells (5 · 10 4 ) were infected with 50 lL 2575/98 (EID 50 = 10 5 /mL) for 1 h at 37°C. At 24 h.p.i., IBV proteins were detected in 2 500-3 000 cells by staining with chicken anti-serum against IBV (Fig. 3B) . We found that the IBV only infected N-cadherin + tracheal epithelial cells, revealing that neither smooth muscle cells nor fibroblast cells are the major target cells for IBV infection (Figs.  3D and 3E) . The infection rate gradually increased to 55.3 ± 12.8% of the total cells at 72 h.p.i. (Fig. 3C) , as estimated by immunocytostaining for IBV antigens in all adherent cells. Similar results were observed in 2296/95-infected cells (data not shown). In addition, both positive-and negative-sense viral RNA present were detected in the cytosol, and positive-sense viral RNA could be detected in the supernatant of ATE cells at 24 h.p.i. (Fig. 3F) , demonstrating that mature IBV virion could be produced and released from the cells. These results indicate that cultured ATE cells support viral infection, replication and spreading of IBV.