Reactivation of latent human cytomegalovirus in CD14(+) monocytes is differentiation dependent

We have previously demonstrated reactivation of latent human cytomegaloviru s (HCMV) in myeloid lineage cells obtained from healthy donors. Virus was o btained from allogenically stimulated monocyte-derived macrophages (Allo-MD M), but not from macrophages differentiated by mitogenic stimulation (ConA- MDM). In the present study, the cellular and cytokine components essential for HCMV replication and reactivation were examined in Allo-MDM. The import ance of both CD4(+) and CD8(+) T cells in the generation of HCMV-permissive Allo-MDM was demonstrated by negative selection or blocking experiments us ing antibodies directed against both HLA class I and HLA class II molecules . Interestingly, contact of monocytes with CD4 or CD8(+) T cells was not es sential for reactivation of HCMV, since virus was observed in macrophages d erived from CD14(+) monocytes stimulated by supernatants produced by alloge neic stimulation of peripheral blood mononuclear cells. Examination of the cytokines produced in Allo-MDM and ConA-MDM cultures indicated a significan t difference in the kinetics of production and quantity of these factors. F urther examination of the cytokines essential for the generation of HCMV-pe rmissive Allo-MDM identified gamma interferon (IFN-gamma) but not interleuk in-1 or -2, tumor necrosis factor alpha, or granulocyte-macrophage colony-s timulating factor as critical components in the generation of these macroph ages. In addition, although IFN-gamma was crucial for reactivation of laten t HCMV, addition of IFN-gamma to unstimulated macrophage cultures was insuf ficient to reactivate virus. Thus, this study characterizes two distinct mo nocyte-derived cell types which can be distinguished by their ability to re activate and support HCMV replication and identifies the critical importanc e of IFN-gamma in the reactivation of HCMV.