Background:  Human vascular endothelial cell interactions with circulating T cells play a crucial role in inflammatory immune responses. Previously, we have shown that endothelial cells increase HIV-1 replication in allogeneic resting memory CD4⁺ T cells 50,000-fold. Endothelial cells are also the primary host cell for human cytomegalovirus (CMV). UV-inactivated CMV can alter endothelial cell metabolism through interactions with toll-like receptor-2 (TLR2)

Methods:  Human umbilical vein endothelial cells were pretreated with interferon-γ (IFN- γ) or 1 of 2 UV-inactivated CMV strains (UV-AD169 and UV-VHL/e), and co-cultured with previously resting primary allogeneic human CD4⁺ T cells infected with HIV-1 strain NL4-3. Virus production in supernatants was assayed by ELISA and Q-RT/PCR

Results:  In co-culture with IFN- γ-treated endothelial cells, high HIV-1-producing T cells were predominantly in the G1 stage of the cell cycle and had very low IL-2 production, undetectable CD25, and low but detectable CD69 expression. Furthermore, suboptimal PHA stimulation of T cells alone revealed that concentrations necessary to produce peak HIV-1 replication were insufficient to activate the T cells as assessed by IL-2 production. UV-inactivated CMV particles could also signal endothelial cells to promote HIV-1 replication in T cells. Endothelial cells pretreated with UV-inactivated endothelial cell-tropic VHL/e yielded a 12,000-fold increase in HIV-1 replication over T cells cultured alone and a 200-fold increase over T cells co-cultured with untreated endothelial cells or UV-inactivated fibroblast-tropic AD169-treated endothelial cells . Unlike IFN- γ treatment, UV-inactivated VHL/e-driven HIV-1 replication in T cells was not associated with MHC class II up-regulation.

Conclusions:  Activated endothelial cells induce a microenvironment conducive to HIV-1 replication in circulating memory T cells. This microenvironment allows HIV to broaden the pool of virus-producing T cells by promoting replication in T cells that do not receive fully activating stimulatory signals from antigen-presenting cells (> 95% of T cells in vivo), but rather are suboptimally stimulated by endothelial cells. Additionally, we show that UV-inactivated CMV particles induced MHC II-independent HIV-1-replication enhancement in T cells, suggesting a distinct and physiologically relevant mechanism whereby chronic CMV infection, and activation of endothelial cells via TLR-2 could contribute to HIV-1 replication in dually infected humans.

Keywords: Endothelium ; CMV; replication