However, it remains unclear if direct infection of monocytes in vitro results in a bona fide latent infection [26,64] or a “quiescent infection” during which viral genomes are carried, but expression of viral genes is delayed and is associated with cytokine stimulation (e.g., granulocyte macrophage-colony stimulating factor, GM-CSF) and macrophage differentiation [32,34]. This evidence concerns the gene CSF2 and disease arising from reactivation of latent virus.