Isolation of a TRAIL antagonist from the serum of HIV-infected patients.

Virus-host interactions are characterized by the selection of adaptive mechanisms by which to evade pathogenic and defense mechanisms, respectively. In primary T cells infected with HIV, HIV infection up-regulates TNF-related apoptosis inducing ligand (TRAIL) and death-inducing TRAIL receptors, but blockade of TRAIL:TRAIL receptor interaction does not alter HIV-induced cell death. Instead, HIV infection results in a novel splice variant that we call TRAIL-short (TRAIL-s), which antagonizes TRAIL-R2. In HIV patients, plasma TRAIL-s concentration increases with increasing viral load and renders cells resistant to TRAIL-induced death. Knockdown of TRAIL-s abrogates this resistance. We propose that TRAIL-s is a novel adaptive mechanism of apoptosis resistance acquired by HIV-infected cells to avoid their elimination by TRAIL-dependent effector mechanism.

HIV gp120 induces, NF-kappaB dependent, HIV replication that requires procaspase 8.

BACKGROUND: HIV envelope glycoprotein gp120 causes cellular activation resulting in anergy, apoptosis, proinflammatory cytokine production, and through an unknown mechanism, enhanced HIV replication. METHODOLOGY/PRINCIPAL FINDINGS: We describe that the signals which promote apoptosis are also responsible for the enhanced HIV replication. Specifically, we demonstrate that the caspase 8 cleavage fragment Caspase8p43, activates p50/p65 Nuclear Factor kappaB (NF-kappaB), in a manner which is inhibited by dominant negative IkappaBalpha. This caspase 8 dependent NF-kappaB activation occurs following stimulation with gp120, TNF, or CD3/CD28 crosslinking, but these treatments do not activate NF-kappaB in cells deficient in caspase 8. The Casp8p43 cleavage fragment also transactivates the HIV LTR through NF-kappaB, and the absence of caspase 8 following HIV infection greatly inhibits HIV replication. CONCLUSION/SIGNIFICANCE: Gp120 induced caspase 8 dependent NF-kappaB activation is a novel pathway of HIV replication which increases understanding of the biology of T-cell death, as well as having implications for understanding treatment and prevention of HIV infection.

The Biology of TRAIL and the Role of TRAIL-Based Therapeutics in Infectious Diseases.

TNF-related apoptosis inducing ligand (TRAIL) is a key mediator of the innate immune response to infection. While TRAIL-mediated apoptosis plays an essential role in the clearance of virus-infected cells, its physiologic role also includes immunosurveilance for cancer cells. Therapeutics that induce TRAIL-mediated apoptosis in cancer cells remain a focus of ongoing investigation in clinical trials, and much has been learned from these studies regarding the efficacy and toxicity of these interventions. These data, combined with data from numerous preclinical studies that detail the important and multifaceted role of TRAIL during infection with human immunodeficiency virus and other viruses, suggest that therapeutic exploitation of TRAIL signaling offers a novel and efficacious strategy for the management of infectious diseases.

Beneficial effect of TRAIL on HIV burden, without detectable immune consequences.

BACKGROUND: During uncontrolled HIV disease, both TNF-related apoptosis inducing ligand (TRAIL) and TRAIL receptor expression are increased. Enhanced TRAIL sensitivity is due to TRAIL receptor up-regulation induced by gp120. As a result of successful antiretroviral therapy TRAIL is down-regulated, and there are fewer TRAIL-sensitive cells. In this setting, we hypothesized that all cells that contain virus, including those productively- and latently-infected, have necessarily been "primed" by gp120 and remain TRAIL-sensitive, whereas uninfected cells remain relatively TRAIL-resistant. METHODS AND FINDINGS: We evaluated the immunologic and antiviral effects of TRAIL in peripheral blood lymphocytes collected from HIV-infected patients with suppressed viral replication. The peripheral blood lymphocytes were treated with recombinant TRAIL or an equivalent amount of bovine serum albumin as a negative control. Treated cells were then analyzed by quantitative flow cytometry, ELISPOT for CD4+ and CD8+ T-cell function, and limiting dilution microculture for viral burden. Alterations in the cytokine milieu of treated cells were assessed with a multiplex cytokine assay. Treatment with recombinant TRAIL in vitro reduced viral burden in lymphocytes collected from HIV-infected patients with suppressed viral load. TRAIL treatment did not alter the cytokine milieu of treated cells. Moreover, treatment with recombinant TRAIL had no adverse effect on either the quantity or function of immune cells from HIV-infected patients with suppressed viral replication. CONCLUSIONS: TRAIL treatment may be an important adjunct to antiretroviral therapy, even in patients with suppressed viral replication, perhaps by inducing apoptosis in cells with latent HIV reservoirs. The absence of adverse effect on the quantity or function of immune cells from HIV-infected patients suggests that there is not a significant level of "bystander death" in uninfected cells.

Infected cell killing by HIV-1 protease promotes NF-kappaB dependent HIV-1 replication.

Acute HIV-1 infection of CD4 T cells often results in apoptotic death of infected cells, yet it is unclear what evolutionary advantage this offers to HIV-1. Given the independent observations that acute T cell HIV-1 infection results in (1) NF-kappaB activation, (2) caspase 8 dependent apoptosis, and that (3) caspase 8 directly activates NF-kappaB, we questioned whether these three events might be interrelated. We first show that HIV-1 infected T cell apoptosis, NF-kappaB activation, and caspase 8 cleavage by HIV-1 protease are coincident. Next we show that HIV-1 protease not only cleaves procaspase 8, producing Casp8p41, but also independently stimulates NF-kappaB activity. Finally, we demonstrate that the HIV protease cleavage of caspase 8 is necessary for optimal NF-kappaB activation and that the HIV-1 protease specific cleavage fragment Casp8p41 is sufficient to stimulate HIV-1 replication through NF-kappaB dependent HIV-LTR activation both in vitro as well as in cells from HIV infected donors. Consequently, the molecular events which promote death of HIV-1 infected T cells function dually to promote HIV-1 replication, thereby favoring the propagation and survival of HIV-1.

Early changes in T-cell activation predict antiretroviral success in salvage therapy of HIV infection.

OBJECTIVE: Because effective antiretroviral therapy (ART) reduces immune activation, we hypothesize that early changes in immune activation are associated with subsequent virologic response to therapy. DESIGN: Observational cohort study. SETTING: Institutional HIV clinic. SUBJECTS: Thirty-four adult HIV patients with virologic failure on their current antiretroviral regimen. INTERVENTION: Change to salvage regimen selected by patient's physician. MAIN OUTCOME MEASURES: Measures of immune activation at baseline and at 2, 4, 8, and 24 weeks after enrollment. Data were analyzed by proportional hazards (PH) models. RESULTS: PH models showed that reductions between baseline and week 2 in expression of CD38 (P = 0.02) or CD95 (P = 0.02) on CD4 T cells were associated with increased likelihood of achieving virologic suppression. Kaplan-Meier analysis demonstrated that patients who had reductions within the first 2 weeks of therapy in CD4 T-cell expression of CD38 (P = 0.003) or CD95 (P = 0.08) were more likely to achieve viral suppression than those who did not. CONCLUSIONS: Reduced CD4 T-cell expression of CD38 and CD95 occurring within 2 weeks of salvage therapy is associated with subsequent viral suppression. Monitoring CD38 and CD95 may allow earlier assessment of the response to ART.

Molecular analysis of the Enterococcus faecalis serotype 2 polysaccharide determinant.

We previously described a 15-kb genetic cluster consisting of 11 open reading frames (cps2A to cps2K) of Enterococcus faecalis FA2-2 that is responsible for the production of the serotype 2 capsular polysaccharide. By using transcriptional fusions to a promoterless lacZ gene, we identified two independent promoters related to the expression of the polysaccharide. Both transcription initiation sites were mapped by primer extension. Reverse transcription-PCR (RT-PCR) demonstrated the transcriptional linkage of genes present in both transcripts. Real-time RT-PCR quantification of transcripts revealed maximum transcription during log phase growth, an observation confirmed by promoter fusion studies. The heterologous expression of this pathway in Escherichia coli caused reactivity with E. faecalis type 2 antiserum, thus demonstrating the essential role of this pathway in the synthesis of the type-specific polysaccharide.

Differential expression of virulence-related genes in Enterococcus faecalis in response to biological cues in serum and urine.

Enterococci rank among leading causes of nosocomial bacteremia and urinary tract infection and are also a leading cause of community acquired subacute endocarditis. Limited evidence suggests that biological cues in serum and urine may play an important role in modulating enterococcal virulence at sites of infection. To determine the extent to which biological cues affect enterococcal virulence-associated gene expression, we used quantitative real-time PCR to compare mRNA levels in Enterococcus faecalis cultures grown in serum or urine to that achieved in laboratory medium. Both environment- and growth phase-specific variations were observed, demonstrating the occurrence of as-yet-uncharacterized mechanisms for control of gene expression in E. faecalis that may play an important role in vivo.

Antibiotic-resistant enterococci: the mechanisms and dynamics of drug introduction and resistance.

Enterococci possess a vast array of mechanisms to resist the lethal effects of most antimicrobial drugs currently approved for therapeutic use in humans, thus presenting a considerable therapeutic challenge. This review summarizes current concepts regarding the mechanisms of resistance, as well as the emergence, proliferation, and epidemiology of resistant enterococci.

Two-component regulator of Enterococcus faecalis cytolysin responds to quorum-sensing autoinduction.

Bacteria of the genus Enterococcus are the main causes of highly antibiotic-resistant infections that are acquired in hospitals. Many clinical isolates of Enterococcus faecalis produce an exotoxin called cytolysin that contributes to bacterial virulence. In addition to its toxin activity, the cytolysin is bactericidal for nearly all Gram-positive organisms. An understanding of conditions that regulate cytolysin expression has advanced little since its initial description. Here we show that the products of two genes, cylR1 and cylR2, which lack homologues of known function, work together to repress transcription of cytolysin genes. Derepression occurs at a specific cell density when one of the cytolysin subunits reaches an extracellular threshold concentration. These observations form the basis of a model for the autoinduction of the cytolysin by a quorum-sensing mechanism involving a two-component regulatory system.