HIV-1 Reactivation in Resting Peripheral Blood Mononuclear Cells of Infected Adults Upon in Vitro CD4 Cross-Linking by Ligands of the CDR2-Loop in Extracellular Domain 1

Abstract

HIV-1 infects resting peripheral blood mononuclear cells (PBMCs) but remains inactive state until subsequent cell activation. We have demonstrated that the cross-linking of cell surface CD4 by gp120-anti-gp120 immune complexes or heat-inactivated HIV-1 (iHIV-1) is sufficient to trigger activation signals leading to virus reactivation (9). In this study, we demonstrate that NF-kappaB nuclear translocation and stimulation of virus production by iHIV-1 were strictly linked to the concentrations of viral proteins used as exogenous stimuli. Moreover, we further investigated the physiologic relevance of these observations. When submitted to an in vitro CD4 cross-linking by iHIV-1, PBMCs from HIV-1-infected patients were found to produce virus. This viral reactivation was associated with increased NF-kappaB nuclear translocation in patients' PBMCs. Additionally, virus reactivation in resting PBMCs infected in vitro with HIV-1 was found to be specifically induced by ligands of the CDR2-loop in domain 1 (D1) of CD4 (virus envelope and anti-CD4 monoclonal antibodies). In contrast, virus reactivation was not observed following CD4 oligomerization by antibodies that bind other epitopes in D1, including the D1/CDR3-loop. Finally, soluble CD4 (sCD4) prevented virus reactivation by D1/CDR2-loop ligands. Our results indicate that the signaling events initiated in PBMCs by oligomerization of CD4 at the D1/CDR2-loop can trigger HIV-1 upregulation in infected individuals.

HIV Envelope Induces Virus Expression from Resting CD4+ T Cells Isolated from HIV-Infected Individuals in the Absence of Markers of Cellular Activation or Apoptosis

“…In contrast, HIV-uninfected PBMC treated with either iHIV or soluble gp120 failed to express the cell surface activation markers CD25 and CD69 (30), although a small increase in cellular proliferation was observed 48 h post-treatment with iHIV. The discrepancy between our data and those of the previous studies (24,29,30) with regard to the effects of envelope on cellular activation probably reflect differences in the cellular systems analyzed and, perhaps, the form in which envelope protein is presented. In PBMC an indirect effect on T cell activation may occur following the interaction between gp120/160 and other CD4 ϩ cells, such as monocyte/macrophages.…”

“…The effect of envelope protein (gp120 or gp120-anti-gp120 complexes) or inactivated HIV (iHIV) virions on HIV expression has been previously investigated using unstimulated PBMC isolated from HIV-infected donors (29) or PBMC infected with HIV in vitro (24). In the earlier study the expression of HIV was associated with a transition to the S/G 2 /M stage of the cell cycle and the expression of the cell surface activation marker CD25 (24).…”

“…[21][22][23][24][25][26][27]; reviewed in Ref. 28) or inactivated virions (24,29,30) activates a large variety of cellular gene products associated with cellular activation and in this way may prime nondividing cells for the ability to support subsequent HIV infection. Counteracting these potentially positive effects on HIV replication, HIV envelope has also been demonstrated to enhance apoptosis in activated CD4…”

NF‐κB activation upon interaction of HIV‐1 envelope glycoproteins with cell surface CD4 involves IκB kinases

“…Multiple studies have addressed the role played by NF‐κB transcription factor in the reactivation of HIV from the latent state and in the control of viral persistence. We previously demonstrated that gp120 env ‐dependent activation of NF‐κB has a significant relevance to the physiopathology of HIV infection by reactivating HIV‐1 transcription in PBMCs from symptomatic infected patients [31]. Besides this, the direct interaction of gp120 env with a CXCR4 receptor was also reported by others to stimulate T cell apoptosis in a CD4‐independent fashion [36].…”

“…Our previous papers focused on T cell activation triggered by gp120 env binding to the CD4 receptor and demonstrated that CD4 cross‐linking with gp120 env stimulates both AP‐1 and NF‐κB DNA‐binding activity. The consequences of such activation signals on reactivating latent proviruses harbored by primary T cells from HIV‐1 infected T cells have also been described [31].…”