A new insect cell line from Trichoplusia ni (BTI-Tn-5B1-4) susceptible to Trichoplusia ni single enveloped nuclear polyhedrosis virus
The replication of Trichoplusia ni SNPV (TnSNPV) in a new Lepidopteran cell line, BTI-Tn-5B1-4 (Tn-5B1-4), is presented. This cell line was highly susceptible to TnSNPV with infection rates exceeding 90% by 48 hr postinfection (pi). Budded virus (BV) was present in the culture medium 14 hr pi and reached a maximum titer of 3.2 X 10(6) TCID50/ml 48 hr pi. Cell-associated virus was produced 12 hr pi and reached a maximum titer of 2.4 X 10(6) TCID50/ml 36 hr pi. Serial pas sage of TnSNPV was initiated in Tn-5B1-4 cells with infectious hemolymph obtained from T. ni larvae infected with TnSNPV occlusion bodies (OBs). TnSNPV was subsequently grown in this cell line for 60 serial passages. Levels of BV infectivity were maintained at approximately 3.2 X 10(5) TCID50/ml through passage 60. Early passage virus (i.e., 1-7 passages) resulted in approximately 500 to 700 OB/cell, whereas later passages (i.e., 7-60) showed an average decrease from 450 to 100 OB/cell. Bioassay results showed high infectivity (approximately 95%) with early passage virus; however, infectivity dropped off rapidly in later passages with no larval infectivity seen after passage 20. In addition, the effects of cryopreservation on virulence and yield of TnSNPV-BV, produced in the Tn-5Bl-4 parental cell line, BTI-Tn-5B1, at 4 and -100 degrees C, were investigated. By 6 weeks, BV titers for samples stored at both temperatures had decreased by as much as one order of magnitude. Although gradual decreases in titer were observed under both storage conditions, - 100 degrees C appeared to be more suitable for long term cryopreservation.
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