human immunodeficiency virus, dendritic cell, gene expression, HIV Infections, t lymphocyte, virus replication
Productive infection of T cells with human immunodeficiency virus 1 (HIV- 1) typically requires that the T cells be stimulated with antigens or mitogens. This requirement has been attributed to the activation of the transcription factor NF-κB, which synergizes with the constitutive transcription factor Sp1 to drive the HIV-1 promoter. Recently, we have found that vigorous replication of HIV-1 takes place in nonactivated memory T cells after syncytium formation with dendritic cells (DCs). These syncytia lack activated cells as determined by an absence of staining for Ki-67 cell cycle antigen. The expression and activity of NF-κB and Sp1 were, therefore, analyzed in isolated T cells and DCs from humans and mice. We have used immunolabeling, Western blot analysis, and electrophoretic mobility shift and supershift assays. T cells lack active NF-κB but express Sp1 as expected. DCs express high levels of all known NF-κB and Rel proteins, with activity residing primarily within RelB, p50, and p65. However, DCs lack Sp1, which may explain the failure of HIV-1 to replicate in purified DCs. Coexpression of NF-κB and Sp1 occurs in the heterologous DC-T-cell syncytia that are induced by HIV-1. Therefore, HIV-1-induced cell fusion brings together factors that upregulate virus transcription. Since DCs and memory T cells frequently traffic together in situ, these unusual heterologous syncytia could develop in infected individuals and lead to chronic HIV-1 replication without ostensible immune stimulation.
Granelli-Piperno, A., M. Pope, K. Inaba, and R. M. Steinman. 1995. "Coexpression of NF-κB/Rel and Sp1 Transcription Factors in Human Immunodeficiency Virus 1-Induced, Dendritic Cell-T-Cell Syncytia." Proceedings of the National Academy of Sciences of the United States of America 92 (24): 10944-10948