Nicholas T. Funderburg

Human β-defensin-3 activates professional antigen-presenting cells via Toll-like receptors 1 and 2

There is increasing evidence that innate and adaptive immune responses are intimately linked. This linkage is in part mediated through the recognition of conserved microbial products by Toll-like receptors (TLRs). Detection of microbial products by TLRs can result in induction of inflammatory cytokines and activation of professional antigen-presenting cells, thereby enhancing adaptive immune responses. Here, we show that human β-defensin-3 (hBD-3), an innate antimicrobial peptide, can induce expression of the costimulatory molecules CD80, CD86, and CD40, on monocytes and myeloid dendritic cells in a TLR-dependent manner. Activation of monocytes by hBD-3 is mediated by interaction with TLRs 1 and 2, resulting in signaling that requires myeloid differentiating factor 88 and results in IL-1 receptor-associated kinase-1 phosphorylation. In studies with HEK cells engineered to express various TLRs, we show that activation of NF-κB by hBD-3 depends on the expression of both TLR1 and TLR2. Thus, human TLR signaling is not restricted to recognition of microbial patterns but also can be initiated by host-derived peptides such as hBD-3.

Gut Epithelial Barrier Dysfunction and Innate Immune Activation Predict Mortality in Treated HIV Infection

BACKGROUND While inflammation predicts mortality in treated human immunodeficiency virus (HIV) infection, the prognostic significance of gut barrier dysfunction and phenotypic T-cell markers remains unclear. METHODS We assessed immunologic predictors of mortality in a case-control study within the Longitudinal Study of the Ocular Complications of AIDS (LSOCA), using conditional logistic regression. Sixty-four case patients who died within 12 months of treatment-mediated viral suppression were each matched to 2 control individuals (total number of controls, 128) by duration of antiretroviral therapy-mediated viral suppression, nadir CD4(+) T-cell count, age, sex, and prior cytomegalovirus (CMV) retinitis. A similar secondary analysis was conducted in the SCOPE cohort, which had participants with less advanced immunodeficiency. RESULTS Plasma gut epithelial barrier integrity markers (intestinal fatty acid binding protein and zonulin-1 levels), soluble CD14 level, kynurenine/tryptophan ratio, soluble tumor necrosis factor receptor 1 level, high-sensitivity C-reactive protein level, and D-dimer level all strongly predicted mortality, even after adjustment for proximal CD4(+) T-cell count (all P ≤ .001). A higher percentage of CD38(+)HLA-DR(+) cells in the CD8(+) T-cell population was a predictor of mortality before (P = .031) but not after (P = .10) adjustment for proximal CD4(+) T-cell count. Frequencies of senescent (defined as CD28(-)CD57(+) cells), exhausted (defined as PD1(+) cells), naive, and CMV-specific T cells did not predict mortality. CONCLUSIONS Gut epithelial barrier dysfunction, innate immune activation, inflammation, and coagulation-but not T-cell activation, senescence, and exhaustion-independently predict mortality in individuals with treated HIV infection with a history of AIDS and are viable targets for interventions.

Immunologic Failure Despite Suppressive Antiretroviral Therapy Is Related to Activation and Turnover of Memory CD4 Cells

BACKGROUND Failure to normalize CD4(+) T-cell numbers despite effective antiretroviral therapy is an important problem in human immunodeficiency virus (HIV) infection. METHODS To evaluate potential determinants of immune failure in this setting, we performed a comprehensive immunophenotypic characterization of patients with immune failure despite HIV suppression, persons who experienced CD4(+) T-cell restoration with therapy, and healthy controls. RESULTS Profound depletion of all CD4(+) T-cell maturation subsets and depletion of naive CD8(+) T cells was found in immune failure, implying failure of T-cell production/expansion. In immune failure, both CD4(+) and CD8(+) cells were activated but only memory CD4(+) cells were cycling at increased frequency. This may be the consequence of inflammation induced by in vivo exposure to microbial products, as soluble levels of the endotoxin receptor CD14(+) and interleukin 6 were elevated in immune failure. In multivariate analyses, naive T-cell depletion, phenotypic activation (CD38(+) and HLA-DR expression), cycling of memory CD4(+) T cells, and levels of soluble CD14 (sCD14) distinguished immune failure from immune success, even when adjusted for CD4(+) T-cell nadir, age at treatment initiation, and other clinical indices. CONCLUSIONS Immune activation that appears related to exposure to microbial elements distinguishes immune failure from immune success in treated HIV infection.

Increased tissue factor expression on circulating monocytes in chronic HIV infection: relationship to in vivo coagulation and immune activation.

HIV infection is associated with an increased risk of thrombosis; and as antiretroviral therapy has increased the lifespan of HIV-infected patients, their risk for cardiovascular events is expected to increase. A large clinical study found recently that all-cause mortality for HIV(+) patients was related to plasma levels of interleukin-6 and to D-dimer products of fibrinolysis. We provide evidence that this elevated risk for coagulation may be related to increased proportions of monocytes expressing cell surface tissue factor (TF, thromboplastin) in persons with HIV infection. Monocyte TF expression could be induced in vitro by lipopolysaccharide and flagellin, but not by interleukin-6. Monocyte expression of TF was correlated with HIV levels in plasma, with indices of immune activation, and with plasma levels of soluble CD14, a marker of in vivo lipopolysaccharide exposure. TF levels also correlated with plasma levels of D-dimers, reflective of in vivo clot formation and fibrinolysis. Thus, drivers of immune activation in HIV disease, such as HIV replication, and potentially, microbial translocation, may activate clotting cascades and contribute to thrombus formation and cardiovascular morbidities in HIV infection.

Microbial translocation, immune activation, and HIV disease

The advent of combination antiretroviral therapy (cART) has significantly improved the prognosis of human immunodeficiency virus (HIV)-infected individuals. However, individuals treated long-term with cART still manifest increased mortality compared to HIV-uninfected individuals. This increased mortality is closely associated with inflammation, which persists in cART-treated HIV-infected individuals despite levels of plasma viremia below detection limits. Chronic, pathological immune activation is a key factor in progression to acquired immunodeficiency syndrome (AIDS) in untreated HIV-infected individuals. One contributor to immune activation is microbial translocation, which occurs when microbial products traverse the tight epithelial barrier of the gastrointestinal tract. Here we review the mechanisms underlying microbial translocation and its role in contributing to immune activation and disease progression in HIV infection.

Residual immune dysregulation syndrome in treated HIV infection.

Antiretroviral therapy has revolutionized the course of HIV infection, improving immune function and decreasing dramatically the mortality and morbidity due to the opportunistic complications of the disease. Nonetheless, even with sustained suppression of HIV replication, many HIV-infected persons experience a syndrome characterized by increased T cell activation and evidence of heightened inflammation and coagulation. This residual immune dysregulation syndrome or RIDS is more common in persons who fail to increase circulating CD4+ T cells to normal levels and in several epidemiologic studies it has been associated with increased morbidity and mortality. These morbid and fatal events are not the typical opportunistic infections and malignancies seen in the early AIDS era but rather comprise a spectrum of cardiovascular events, liver disease, metabolic disorders, kidney disease, bone disease, and a spectrum of malignant complications distinguishable from the opportunistic malignancies that characterized the earlier days of the AIDS epidemic. While immune activation, inflammation, and coagulopathy are characteristic of untreated HIV infection and improve with drug-induced control of HIV replication, the drivers of RIDS in treated HIV infection are incompletely understood. And while inflammation, immune activation, and coagulopathy are more common in treated persons who fail to restore circulating CD4+ T cells, it is not entirely clear how these two phenomena are linked.

Magnesium Decreases Inflammatory Cytokine Production: A Novel Innate Immunomodulatory Mechanism

MgSO4 exposure before preterm birth is neuroprotective, reducing the risk of cerebral palsy and major motor dysfunction. Neonatal inflammatory cytokine levels correlate with neurologic outcome, leading us to assess the effect of MgSO4 on cytokine production in humans. We found reduced maternal TNF-α and IL-6 production following in vivo MgSO4 treatment. Short-term exposure to a clinically effective MgSO4 concentration in vitro substantially reduced the frequency of neonatal monocytes producing TNF-α and IL-6 under constitutive and TLR-stimulated conditions, decreasing cytokine gene and protein expression, without influencing cell viability or phagocytic function. In summary, MgSO4 reduced cytokine production in intrapartum women, term and preterm neonates, demonstrating effectiveness in those at risk for inflammation-associated adverse perinatal outcomes. By probing the mechanism of decreased cytokine production, we found that the immunomodulatory effect was mediated by magnesium and not the sulfate moiety, and it was reversible. Cellular magnesium content increased rapidly upon MgSO4 exposure, and reduced cytokine production occurred following stimulation with different TLR ligands as well as when magnesium was added after TLR stimulation, strongly suggesting that magnesium acts intracellularly. Magnesium increased basal IĸBα levels, and upon TLR stimulation was associated with reduced NF-κB activation and nuclear localization. These findings establish a new paradigm for innate immunoregulation, whereby magnesium plays a critical regulatory role in NF-κB activation, cytokine production, and disease pathogenesis.

Shared monocyte subset phenotypes in HIV-1 infection and in uninfected subjects with acute coronary syndrome

The mechanisms responsible for increased cardiovascular risk associated with HIV-1 infection are incompletely defined. Using flow cytometry, in the present study, we examined activation phenotypes of monocyte subpopulations in patients with HIV-1 infection or acute coronary syndrome to find common cellular profiles. Nonclassic (CD14(+)CD16(++)) and intermediate (CD14(++)CD16(+)) monocytes are proportionally increased and express high levels of tissue factor and CD62P in HIV-1 infection. These proportions are related to viremia, T-cell activation, and plasma levels of IL-6. In vitro exposure of whole blood samples from uninfected control donors to lipopolysaccharide increased surface tissue factor expression on all monocyte subsets, but exposure to HIV-1 resulted in activation only of nonclassic monocytes. Remarkably, the profile of monocyte activation in uncontrolled HIV-1 disease mirrors that of acute coronary syndrome in uninfected persons. Therefore, drivers of immune activation and inflammation in HIV-1 disease may alter monocyte subpopulations and activation phenotype, contributing to a pro-atherothrombotic state that may drive cardiovascular risk in HIV-1 infection.

Toll-Like Receptor Ligands Induce Human T Cell Activation and Death, a Model for HIV Pathogenesis

Background Recently, heightened systemic translocation of microbial products was found in persons with chronic HIV infection and this was linked to immune activation and CD4+ T cell homeostasis. Methodology We examined here the effects of microbial Toll-like receptor (TLR) ligands on T cell activation in vitro. Conclusions/Findings We show that exposure to TLR ligands results in activation of memory and effector CD4+ and CD8+ T cells. After exposure to each of 8 different ligands that activate TLRs 2, 3, 4, 5, 7, 8, and 9, CD8+ T cells are activated and gain expression of the C type lectin CD69 that may promote their retention in lymphoid tissues. In contrast, CD4+ T cells rarely increase CD69 expression but instead enter cell cycle. Despite activation and cell cycle entry, CD4+ T cells divide poorly and instead, disproportionately undergo activation-induced cell death. Systemic exposure to TLR agonists may therefore increase immune activation, effector cell sequestration in lymphoid tissues and T cell turnover. These events may contribute to the pathogenesis of immune dysfunction and CD4+ T cell losses in chronic infection with the human immunodeficiency virus.

Probiotic/prebiotic supplementation of antiretrovirals improves gastrointestinal immunity in SIV-infected macaques

HIV infection results in gastrointestinal (GI) tract damage, microbial translocation, and immune activation, which are not completely ameliorated with suppression of viremia by antiretroviral (ARV) therapy. Furthermore, increased morbidity and mortality of ARV-treated HIV-infected individuals is associated with these dysfunctions. Thus, to enhance GI tract physiology, we treated SIV-infected pigtail macaques with ARVs, probiotics, and prebiotics or with ARVs alone. This synbiotic treatment resulted in increased frequency and functionality of GI tract APCs, enhanced reconstitution and functionality of CD4+ T cells, and reduced fibrosis of lymphoid follicles in the colon. Thus, ARV synbiotic supplementation in HIV-infected individuals may improve GI tract immunity and thereby mitigate inflammatory sequelae, ultimately improving prognosis.