The role of the interferon consensus sequence binding protein (ICSBP), a member of interferon regulatory factor family, in protecting against a vesicular stomatitis virus (VSV) infection has not been firmly elucidated. Thus, it was investigated utilizing the human promyelocytic leukemia HL-60 cells which do not express ICSBP.

HL-60 cells were stably transfected with plasmid containing cDNA for either ICSBP or DNA binding domain (DBD) and tested for their VSV-susceptibilities. The susceptibility of each transfectant group to a VSV infection was determined by a plaque assay at 1 h, 24 h, and 48 h post-infection in the presence (500 IU/ml) or absence of interferon α(IFNα).

In the absence of IFNα, the three groups showed similar sensitivities to a VSV infection. However, when pre-treated with IFN, the viral titers in both the ICSBP and control clones steadily decreased over 48 h of incubation, indicating the existence of IFNα-mediated protection against VSV infection. The IFNα-treated ICSBP clones appeared to be more resistant to infection compared with the control clones, although the difference was not great. On the contrary, the viral titers in the IFNα-treated DBD clones increased at 24 h then decreased by 48 h.

The expression of truncated ICSBP (DBD) does not appear to underlie the impaired protection against a VSV infection in the DBD clones, since even the control clones lacking ICSBP were protected from a VSV infection. This suggests that ICSBP does not play a critical role in the IFNα-mediated anti-VSV response of HL-60 cells, although it appears to confer some resistance to a VSV infection.