RESTING B-CELLS, EBV-INFECTED B-BLASTS AND ESTABLISHED LYMPHOBLASTOIDCELL-LINES DIFFER IN THEIR RB, P53 AND EBNA-5 EXPRESSION PATTERNS

Using immunofluorescence technique we have analysed the Rb, p53, EBNA- 2 and EBNA-5 expression pattern in EBV infected human B-cells and esta blished lymphoblastoid cell lines (LCL-s). Resting B-cells showed only a faint Rb and no p53 immunostaining. The expression of both Rb and p 53 increased after EBV infection. The change was first detectable 6 h after infection. The frequency of brilliantly Rb positive cells increa sed more than p53 positives. EBNA-2 and EBNA-5 first detectable 12 h a fter infection. The frequency of EBNA positive cells in the freshly in fected cultures was concordant with the proportion of CD23 and PCNA po sitives, but remained consistently below the frequency of Rb and p53 p ositive cells. Double immunofluorescence staining showed that all EBNA -5 positive cells were strongly Rb and p53 positive. LCL-s did not sta in for p53, whereas the Rb staining was maintained at a high level. Th e EBNA-5 staining pattern changed from brilliant almost homogeneous nu clear staining in the freshly infected B-cells, to a nonhomogeneous pa ttern with a small number of strongly fluorescent nuclear bodies in es tablished LCL-s. There was no change in the EBNA-2 staining pattern. O ur findings indicate that the immortalization of B-cells by EBV may in itially involve a high expression of EBNA-5, p53 and Rb, but only cell s with low p53 and focal expression of EBNA-5 in nuclear bodies have t he selective advantage required to grow into immortalized lines.