During infection with hepadnaviruses besides the infectious agent a high number of subviral particles without nucleocapsids are produced, which are able to change the infection dramatically. In addition, it was observed that the activation of the nuclear factor of activated T cells, regulated usually in cells of the immune system, was strongly influenced after infection. When primary duck liver cells were infected with purified virions of duck hepatitis B virus the activation of this factor was reduced in a similar way as it was achieved by inhibition of calcineurin, a cellular phosphatase necessary to control the factor, whereas the addition of subviral particles inhibited this reduction. It was found that the large surface protein of the virus was responsible for the reduced activity. Although this protein was embedded in similar amounts into the envelopes of both particles, only virions were able to inhibit the activity of the nuclear factor. An explanation of the different performances of the particles in primary duck liver cells apparently depends on the individual mode of insertion of the large surface proteins into the viral membrane. Furthermore, the nuclear factor of activated T cells could only be detected in liver sinusoidal endothelial cells, which was shown being attracted by virions but not by subviral particles
