Factors affecting human cytomegalovirus gene expression in human monocyte cell lines

To understand the mechanisms for establishing and reactivating monocytes an d macrophages from latency by human cytomegalovirus (HCMV), human monocyte cell lines were infected and HCMV gene expression was investigated. Indirec t immunofluorescence assay (IFA) with monoclonal antibody to HCMV major imm ediate early (MIE) IE1 or IE2 proteins revealed that HCMV MIE genes were ex pressed at low levels in relatively more differentiated THP-I cells with TP A treatment after virus infection (posttreatment). Less differentiated cell s such as U937 or HL60 did not support MIE gene expression even after TPA t reatment. If THP-1 cells were pretreated before virus infection with TPA an d became differentiated at the time of HCMV infection, MIE gene expression increased by 5-6 fold. Therefore, the relative degree of monocyte cell diff erentiation appears to be an important factor for regulating HCMV gene expr ession, Further IFA studies using monoclonal antibodies specific for IE1 or IE2 proteins indicate that the sequence and general pattern of IE1 and IE2 gene expression in THP-T cells treated with TPA were similar to those in p ermissive human fibroblast cells with some delay in time, Formation of the replication compartment detected with monoclonal antibody to HCMV polymeras e accessory protein UL44 in THP-1 cells suggests a fully productive replica tion process of HCMV in these cells, Monocytes are known to be induced to d ifferentiate by hydrocortisone (HC), tumor necrosis factor (TNF)-alpha or i nterferon (IFN)-gamma. HC, which is known to stimulate HCMV replication in permissive, human fibroblast (HF) cells, enhanced HCMV gene expression by 2 -3 fold in TPA-pre or posttreated THP-1 cells, but TNF-alpha or IFN-gamma h ad little effect. Nitric oxide (NO) is released by immune cells in the defe nse against foreign stimuli and was shown to inhibit HCMV gene expression i n HF cells. Increasing NO by nitroprusside significantly reduced HCMV gene expression in THP-I cells. Therefore, it appears that the expression of HCM V immediate early genes in THP-1 cells treated with TPA closely resembles t hose in permissive HF cells.