Human Ads of species B (Ad serotype 3) and C (Ad R700, an Ad serotype 5 derivative, Ad serotype 2, Ad2Ts1 and Ad5-GFP an early gene expression defective Ad were grown, purified and stored as previously described [5, 72] . The ratio of infectious/total viral particles was determined on susceptible cells and was typically 1:20-50. If not otherwise stated, Ad2Ts1 used for the experiments was grown at non-permissive temperature 38.5uC (resulting in the absence of incorporation of the adenoviral protease L3/23 into viral capsids). Empty particles were identified by their light density in CsCl density gradients and the absence of viral DNA and were purified simultaneously with mature virions. UV inactivation of Ad was done as described previously [5, 72] using the minimal essential dose preventing viral gene expression and replication in susceptible cells. Heat inactivation was done at 56 uC for 60 min [44] . All virus preparations were LPS-free (less than 1 pg LPS/ 10 11 viral particles) as determined by the Limulus amebocyte lysate test (Pyroquant Diagnostic GMBH, Mörfelden, Germany).