Chronic Immune Activation in HIV-1 Infection Contributes to Reduced Interferon Alpha Production via Enhanced CD40:CD40 Ligand Interaction

Abstract

Although a signature of increased interferon (IFN-)alpha production is observed in HIV-1 infection, the response of circulating plasmacytoid dendritic cells (PDC) to Toll-like receptor ligand stimulation is substantially impaired. This functional PDC deficit, which we specifically observed in HIV-1 infected individuals with less than 500 CD4+ T cells/µl, is not well understood. We provide evidence that the peripheral IFN-alpha production in HIV-1 infection is actively suppressed by the enhanced interaction of CD40 ligand (CD40L), a member of the tumor necrosis factor family, and its receptor CD40, which are both upregulated upon immune activation. Plasma levels of soluble CD40L were significantly higher in untreated HIV-1 infected individuals (n = 52) than in subjects on long-term antiretroviral therapy (n = 62, p<0.03) and in uninfected control donors (n = 16, p<0.001). Concomitantly, cell-associated CD40L and the expression of the receptor CD40 on the PDC were significantly upregulated in HIV-1 infection (p<0.05). Soluble and cell-associated CD40L inhibited the PDC-derived IFN-alpha production by CpG oligodeoxynucleotides dose-dependently. This suppressive effect was observed at much lower, physiological CD40L concentrations in peripheral blood mononuclear cells (PBMC) of HIV-1 infected individuals compared to controls (p<0.05). The CpG-induced IFN-alpha production in PBMC of HIV-1 infected donors was directly correlated with PDC and CD4+ T cell counts, and inversely correlated with the viral loads (p<0.001). In HIV-1 infected donors with less than 500 CD4+ T cells/µl, the CpG-induced IFN-alpha production was significantly correlated with the percentage of CD40-expressing PDC and the level of CD40 expression on these cells (p<0.05), whereas CD40L plasma levels played a minor role. In addition, low-dose CD40L contributed to the enhanced production of interleukin 6 and 8 in PBMC of HIV-1 infected donors compared to controls. Our data support the conclusion that the chronic immune activation in HIV-1 infection impairs peripheral PDC innate immune responses at least in part via enhanced CD40:CD40L interactions.

Soluble CD40 ligand contributes to dendritic cell-mediated T-cell dysfunction in HIV-1 infection

“…Although it has been observed that total sCD40L is increased in the plasma of HIV-infected subjects as compared to healthy controls [13-15], the circulating form(s) of sCD40L have not been assessed during HIV infection. The immune activating effects of multimeric sCD40L have been extensively studied [6-8], but recent studies suggest an immunosuppressive effect of monomeric sCD40L [12, 25]. To address the question of whether the monomeric or multimeric form is the predominant form of sCD40L circulating in plasma of HIV-infected subjects as compared to healthy control subjects, we enriched plasma from 8 HIV infected donors and 8 healthy control donors for medium- and low- abundance proteins, followed by immunoblot of plasma preparations for sCD40L.…”

“…We observed that multiple forms of sCD40L, including monomers (18kD) and multimers of various sizes (26-40kD) circulate in the plasma of both HIV-infected subjects and healthy controls with relative ratios that vary by donor (Figure 1A). To better understand the implication of our finding in HIV infection, where overall levels of plasma sCD40L are heightened [13-15], we next sought to determine whether there were differential immunological effects of sCD40L forms on healthy control DCs in vitro, using sCD40L concentrations tested in previous reports[12, 25]. We observed that maturation of DCs (purity>95% CD11c+LIN neg , Figure 1B) as assessed by CD86 expression was much higher after stimulation with multimeric sCD40L as compared to monomeric sCD40L (Figure 1C).…”

“…This distinction is important because these forms have differential immunologic effects. Multimeric forms of sCD40L are immunostimulatory to APCs [6, 21] whereas monomeric forms of sCD40L play an overall immunosuppressive role [12-14]. Monomeric forms of sCD40L stimulate monocytes to express a pro-inflammatory phenotype and render both monocytes and plasmacytoid dendritic cells refractory to stimulation with Toll-like receptor (TLR) ligand stimulation [12, 14, 22].…”

“…Multimeric forms of sCD40L are immunostimulatory to APCs [6, 21] whereas monomeric forms of sCD40L play an overall immunosuppressive role [12-14]. Monomeric forms of sCD40L stimulate monocytes to express a pro-inflammatory phenotype and render both monocytes and plasmacytoid dendritic cells refractory to stimulation with Toll-like receptor (TLR) ligand stimulation [12, 14, 22]. Monomeric sCD40L exposure also favors the development of myeloid-derived suppressor cells (MDSCs) and regulatory T cells, both of which are elevated during HIV infection[12, 13].…”

“…Though it is well established that levels of sCD40L are elevated during HIV infection[13, 15, 23] , it is not understood which forms of sCD40L are circulating, nor their differential effects on DC function. We found that both monomeric and multimeric forms of sCD40L are circulating in plasma.…”