Differential silver staining in lymphocytes and lymphoblastoid cell cultures

An analysis of the patterns of silver-stained nucleolar organizer regions (AgNORs), an indication of rDNA transcriptional activity, was carried out in metaphases from peripheral lymphocytes and young lymphoblastoid cell cultures (LCL) transformed by Epstein-Barr virus. Four individuals previously shown to carry a double NOR (dNOR) were studied. The dNOR varied in staining frequency and showed intra-individual variation in appearance in both cell types. For each individual a significantly greater mean number of AgNORs was observed in LCL (7.0-8.04) when compared with lymphocytes (5.8-6.4). To control for possible serum stimulation effects, lymphocytes from one individual were cultured in 20% serum as was the LCL of all subjects. The mean number of AgNORs in these lymphocytes remained significantly lower than in the LCL, as did the mean size of the dNOR, based on a relative score. Our results suggest that LCL have increased expression of rDNA, as evidenced by silver staining.