Importantly, however, the high level of IRF4 in cluster 6 may help to explain why cells in this cluster remain latent even though they express high levels of two other transcription factors, PRDM1 and XBP1, that have been shown to activate the BZLF1 promoter and induce lytic EBV infection in other contexts. The gene discussed is XBP1; the disease is Epstein-Barr virus infection.