After completeing the colorization reaction of the ISH as outlined above, sections were incubated with 3% hydrogen peroxide to quench endogenous peroxidase activity. The sections were then blocked with 10% normal horse serum for 10 min at RT, before incubating with monoclonal antibodies (against CD3 + , CD68 + , CD34 + , D35 + ) for 1 h at RT. Unbound antibody was removed by 3 washes in PBS before the addition of HRP-labeled polymer for 30 min at RT (Dako CSA Detection System, Denmark). After washing 3 times with PBS to remove unbound labeled polymer, peroxidase staining in tissue sections was revealed by DAB solution (CSA Detection Systems, DAKO, Denmark). After stopping the reaction in running water, sections were counter-stained by 2% nuclear quick red solution for 30 s. For each tissue, double-labeled stain with IHC and ISH was repeated three times for data analysis. To strengthen further the results of colocalization studies, we performed ISH and IHC on consecutive sections. Tissue sections showing ISH-positive cells were carefully compared with consecutive tissue sections on which IHC with antibodies against specific cell markers was applied. Co-localization of a specific cellular marker and viral genome was clearly identified.