Figure 5. Latent KSHV expression patterns of SLK_P and de novo infected SLK cells.

A: Expression of select latent (ORF71, ORF73) and lytic (ORF50, ORF59) transcripts was analyzed by quantitative RT-PCR in BCBL1 cells, long-term infected SLK_P cells and de novo infected SLK cultures at day 5 post infection (SLK-5dpi). Levels were normalized to represent expression relative to ORF73, which is expressed during the latent as well as the lytic cycle. Compared to BCBL1, SLK-5dpi cells show little expression of lytic antigens, and expression was undetectable in SLKp cells. The detection of lytic transcripts in latent BCBL1 cultures is due to the low percentage (less than 1%) of cells which undergo spontaneous lytic reactivation. The percentage of lytic cells and thus transcript levels can be increased by treatment such as sodium butyrate (lower panel). Spontaneously reactivating cells are completely absent from SLKp cells, which is in accordance with the lack of detectable lytic gene expression. B: Immunofluorescence staining of SLK-5dpi cultures for LANA, the product of ORF73. DAPI staining is shown in the lower panel. More than 90% of the cells tested positive for LANA, while expression of the lytic DNA polymerase processivity factor encoded by ORF59 could be detected in less than 0.01% of cells (compare also left column in Figure 9F).