HBoV1-specific quantitative PCR (qPCR; Figures 4A and S3B ). In the case of B33-11 B-HAE, apical release was obviously initiated at 3 days p.i., then continued to increase to a peak of ,10 8 gc/ml at 5-7 days p.i., then decreased slightly through day 10 p.i. and was maintained at a level of ,10 7 gc/ml through day 22 p.i. ( Figure 4A ). The total virus yield from one Millicell insert of 0.6 cm 2 over a 24-h interval was greater than 2610 10 gc. This result suggested that productive HBoV1 infection of primary B-HAE is persistent. Notably, in the B-HAE cultures from both donors, virus was also continuously released from the basolateral side, keeping pace with apical secretion throughout, though at levels about one log lower than the release from the apical surface ( Figures 4A and S3B ). The genomes of the progeny virions released from infected B-HAE were amplified and sequenced using the primers listed in Figure 1 and primers spanning the NSVP genes between the termini. The result showed an identical sequence with that of the HBoV1 Salvador isolate (Genbank JQ923422). Additionally, no virus was detected in mock-infected B-HAE (data not shown).