Functional Analysis of the ACTGCTGA Sequence Motif in the Human Immunodeficiency Virus Type-1 Long Terminal Repeat Promoter

Enhanced Transcriptional Strength of HIV-1 Subtype C Minimizes Gene Expression Noise and Confers Stability to the Viral Latent State

Stochastic fluctuations in gene expression emanating from the HIV-1 long terminal repeat (LTR), amplified by the Tat positive feedback circuit, determine the choice between viral infection fates: active transcription (ON) or transcriptional silence (OFF). The emergence of several transcription factor binding site (TFBS) variant strains in HIV-1 subtype C (HIV-1C), especially those containing the duplication of the NF-κB motif, mandates the evaluation of the effect of enhanced transcriptional strength on gene expression noise and its influence on viral fate selection switch. Using a panel of subgenomic LTR-variant strains containing different copy numbers of the NF-κB motif (ranging from 0 to 4), we used flow cytometry, mRNA quantification, and pharmacological perturbations to demonstrate an inverse correlation between promoter strength and gene expression noise in Jurkat T cells and primary CD4⁺ T cells. The inverse correlation is consistent in clonal cell populations at constant intracellular concentrations of Tat and when NF-κB levels were regulated pharmacologically. Further, we show that strong LTRs containing at least two copies of the NF-κB motif in the enhancer establish a more stable latent state and demonstrate more rapid latency reversal than weak LTRs containing fewer motifs. We also demonstrate a cooperative binding of NF-κB to the motif cluster in HIV-1C LTRs containing two, three, or four NF-κB motifs (Hill coefficient [H] = 2.61, 3.56, and 3.75, respectively). The present work alludes to a possible evolution of the HIV-1C LTR toward gaining transcriptional strength associated with attenuated gene expression noise with implications for viral latency. IMPORTANCE Over the past two consecutive decades, HIV-1 subtype C (HIV-1C) has been undergoing directional evolution toward augmenting the transcriptional strength of the long terminal repeat (LTR) by adding more copies of the existing transcription factor binding site (TFBS) by sequence duplication. Additionally, the duplicated elements are genetically diverse, suggesting broader-range signal receptivity by variant LTRs. The HIV-1 promoter is inherently noisy, and the stochastic fluctuations in gene expression of variant LTRs may influence the active transcription (ON)/transcriptional silence (OFF) latency decisions. The evolving NF-κB motif variations of HIV-1C offer a powerful opportunity to examine how the transcriptional strength of the LTR might influence gene expression noise. Our work here shows that the augmented transcriptional strength of the HIV-1C LTR leads to concomitantly reduced gene expression noise, consequently leading to stabler latency maintenance and rapid latency reversal. The present work offers a novel lead toward appreciating the molecular mechanisms governing HIV-1 latency.

The Evolution of Regulatory Elements in the Emerging Promoter-Variant Strains of HIV-1 Subtype C

In a multicentric, observational, investigator-blinded, and longitudinal clinical study of 764 ART-naïve subjects, we identified nine different promoter variant strains of HIV-1 subtype C (HIV-1C) emerging in the Indian population, with some of these variants being reported for the first time. Unlike several previous studies, our work here focuses on the evolving viral regulatory elements, not the coding sequences. The emerging viral strains contain additional copies of the existing transcription factor binding sites (TFBS), including TCF-1α/LEF-1, RBEIII, AP-1, and NF-κB, created by sequence duplication. The additional TFBS are genetically diverse and may blur the distinction between the modulatory region of the promoter and the viral enhancer. In a follow-up analysis, we found trends, but no significant associations between any specific variant promoter and prognostic markers, probably because the emerging viral strains might not have established mono infections yet. Illumina sequencing of four clinical samples containing a coinfection indicated the domination of one strain over the other and establishing a stable ratio with the second strain at the follow-up time points. Since a single promoter regulates viral gene expression and constitutes the master regulatory circuit with Tat, the acquisition of additional and variant copies of the TFBS may significantly impact viral latency and latent reservoir characteristics. Further studies are urgently warranted to understand how the diverse TFBS profiles of the viral promoter may modulate the characteristics of the latent reservoir, especially following the initiation of antiretroviral therapy.

Inhibition of the kinase ITK in a mouse model of asthma reduces cell death and fails to inhibit the inflammatory response

Interleukin-2 (IL-2)-inducible T cell kinase (ITK) mediates T cell receptor (TCR) signaling primarily to stimulate the production of cytokines, such as IL-4, IL-5, and IL-13, from T helper 2 (TH2) cells. Compared to wild-type mice, ITK knockout mice are resistant to asthma and exhibit reduced lung inflammation and decreased amounts of TH2-type cytokines in the bronchoalveolar lavage fluid. We found that a small-molecule selective inhibitor of ITK blocked TCR-mediated signaling in cultured TH2 cells, including the tyrosine phosphorylation of phospholipase C-γ1 (PLC-γ1) and the secretion of IL-2 and TH2-type cytokines. Unexpectedly, inhibition of the kinase activity of ITK during or after antigen rechallenge in an ovalbumin-induced mouse model of asthma failed to reduce airway hyperresponsiveness and inflammation. Rather, in mice, pharmacological inhibition of ITK resulted in T cell hyperplasia and the increased production of TH2-type cytokines. Thus, our studies predict that inhibition of the kinase activity of ITK may not be therapeutic in patients with asthma.

Interplay between viral Tat protein and c-Jun transcription factor in controlling LTR promoter activity in different human immunodeficiency virus type I subtypes

HIV-1 transcription depends on cellular transcription factors that bind to sequences in the long-terminal repeat (LTR) promoter. Each HIV-1 subtype has a specific LTR promoter configuration, and minor sequence changes in transcription factor binding sites (TFBSs) or their arrangement can influence transcriptional activity, virus replication and latency properties. Previously, we investigated the proviral latency properties of different HIV-1 subtypes in the SupT1 T cell line. Here, subtype-specific latency and replication properties were studied in primary PHA-activated T lymphocytes. No major differences in latency and replication capacity were measured among the HIV-1 subtypes. Subtype B and AE LTRs were studied in more detail with regard to a putative AP-1 binding site using luciferase reporter constructs. c-Jun, a member of the AP-1 transcription factor family, can activate both subtype B and AE LTRs, but the latter showed a stronger response, reflecting a closer match with the consensus AP-1 binding site. c-Jun overexpression enhanced Tat-mediated transcription of the viral LTR, but in the absence of Tat inhibited basal promoter activity. Thus, c-Jun can exert a positive or negative effect via the AP-1 binding site in the HIV-1 LTR promoter, depending on the presence or absence of Tat.

Epithelial NF-κB orchestrates house dust mite-induced airway inflammation, hyperresponsiveness, and fibrotic remodeling

NF-κB activation within the epithelium has been implicated in the pathogenesis of asthma, yet the exact role of epithelial NF-κB in allergen-induced inflammation and airway remodeling remains unclear. In the current study, we used an intranasal house dust mite (HDM) extract exposure regimen time course in BALB/c mice to evaluate inflammation, NF-κB activation, airway hyperresponsiveness (AHR), and airway remodeling. We used CC10-IκBαSR transgenic mice to evaluate the functional importance of epithelial NF-κB in response to HDM. After a single exposure of HDM, mRNA expression of proinflammatory mediators was significantly elevated in lung tissue of wild-type (WT) mice, in association with increases in nuclear RelA and RelB, components of the classical and alternative NF-κB pathway, respectively, in the bronchiolar epithelium. In contrast, CC10-IκBαSR mice displayed marked decreases in nuclear RelA and RelB and mRNA expression of proinflammatory mediators compared with WT mice. After 15 challenges with HDM, WT mice exhibited increases in inflammation, AHR, mucus metaplasia, and peribronchiolar fibrosis. CC10-IκBαSR transgenic mice displayed marked decreases in neutrophilic infiltration, tissue damping, and elastance parameters, in association will less peribronchiolar fibrosis and decreases in nuclear RelB in lung tissue. However, central airway resistance and mucus metaplasia remained elevated in CC10-IκBαSR transgenic mice, in association with the continued presence of lymphocytes, and partial decreases in eosinophils and IL-13. The current study demonstrates that following airway exposure with an asthma-relevant allergen, activation of classical and alternative NF-κB pathways occurs within the airway epithelium and may coordinately contribute to allergic inflammation, AHR, and fibrotic airway remodeling.

Sequence insertions in the HIV type 1 subtype C viral promoter predominantly generate an additional NF-κB binding site

After screening a large number of clinical samples of HIV-1 subtype C in India, a subset of viral strains containing sequence insertions upstream of the viral enhancer has been identified. The sequence insertions contained binding sites for at least two different transcription factors NF-κB and RBEIII, importantly, in a mutually exclusive fashion. Furthermore, while some of the viral strains contained insertions of κB-like sites, a few others contained dual insertions of the RBEIII and κB sites together but only one of the two was intact. NF-κB acquisition appears to be the most common phenotype unique for subtype C with nearly half of the variant strains containing such insertions. Given that subtype C already contains three functional NF-κB sites in the viral enhancer, acquisition of a fourth NF-κB motif in some variant viral strains is intriguing. Further investigation is warranted to examine the significance of the sequence insertions for the replicative fitness of the variant viral strains.

Antibodies generated against conserved antigens expressed by bacteria and allergen-bearing fungi suppress airway disease

There has been a sharp rise in allergic asthma and asthma-related deaths in the developed world, in contrast to many childhood illnesses that have been reduced or eliminated. The hygiene hypothesis proposes that excessively sanitary conditions early in life result in autoimmune and allergic phenomena because of a failure of the immune system to receive proper microbial stimulation during development. We demonstrate that Abs generated against conserved bacterial polysaccharides are reactive with and dampen the immune response against chitin and Aspergillus fumigatus. A reduction in Ag uptake, cell influx, cell activation, and cytokine production occurred in the presence of anti-polysaccharide Abs, resulting in a striking decrease in the severity of allergic airway disease in mice. Overall, our results suggest that Ag exposure--derived from environmental sources, self-antigens, or vaccination--during the neonatal period has dramatic effects on the adult Ab response and modifies the development of allergic airway disease.

Maternal transmission of resistance to development of allergic airway disease

Parental phenotype is known to influence the inheritance of atopic diseases, such as allergic asthma, with a maternal history being a more significant risk factor for progeny than paternal history. We hypothesized that recall Th1- or Th2-type immune responses during pregnancy would result in transfer of maternal factors that would differentially impact development of immune responsiveness in offspring. Following weaning, susceptibility and severity of allergic airway disease (a murine model of human asthma) was evaluated in progeny, disease being elicited by immunization with OVA-Al(OH)(3) and challenge with aerosolized OVA. We found that progeny of mothers with Th1-biased immunity to OVA subjected to recall aerosol challenge during pregnancy had reduced levels of Ag-specific IgE and airway eosinophilia compared with progeny of mothers with Th2-biased immunity to OVA or naive mothers. Interestingly, progeny of mothers with Th1-type immunity to a heterologous albumin, BSA, were not protected from developing OVA-induced allergic airway disease. These findings demonstrated that maternal transfer of protection from development of allergic airway disease to offspring in this model of maternal Th1-type immunity was Ag specific.

In search of a function for the most frequent naturally-occurring length polymorphism (MFNLP) of the HIV-1 LTR: retaining functional coupling, of Nef and RBF-2, at RBEIII?

Although the prototypical HIV-1 LTR sequences were determined 22 years ago from the initial isolate, elucidating which transcription factors are critical to replication in vivo, has been difficult. One approach has been to examine HIV-1 LTRs that have gone through the gamut of in vivo mutation and selection, in search of absolutely conserved sequences. In this vein, RBEIII sequences are virtually 100% conserved in naturally occurring HIV-1 LTRs. This is because when they are mutated, the MFNLP recreates an RBEIII site. Here, I enumerate some retroviral mutation mechanisms, which could generate the MFNLP. I then review the literature corresponding to the MFNLP, highlighting the discovery in 1999, that RBEIII and MFNLP sequences, bind USF and TFII-I cooperatively, within the context of earlier and later work that suggests a role in HIV-1 activation, through T-cell receptor engagement and the MAPK cascade. One exception to the nearly absolute conservation of RBEIII, has been a group of long term non progressors (LTNP). These patients harbor deletions to the Nef gene. However, the Nef gene overlaps with the LTR, and the LTNP deletions abrogate RBEIII, in the absence of an MFNLP. I suggest that the MFNLP retains functional coupling between the MAPK-mediated effects of Nef and the HIV-1 LTR, through RBEIII. I propose that difficult-to-revert-mutations, to either Nef or RBEIII, result in the convergent LTNP Nef/LTR deletions recently observed. The potential exploitation of this highly conserved protein-binding site, for chimeric transcription factor repression (CTFR) of HIV-1, functionally striving to emulate the LTNP deletions, is further discussed.

A Novel, Orally Active CXCR1/2 Receptor Antagonist, Sch527123, Inhibits Neutrophil Recruitment, Mucus Production, and Goblet Cell Hyperplasia in Animal Models of Pulmonary Inflammation

Sch527123 [2-hydroxy-N,N-dimethyl-3-[[2-[[1(R)-(5-methyl-2-furanyl)propyl]amino]-3,4-dioxo-1-cyclobuten-1-yl]amino]ben-zamide] is a potent, selective antagonist of the human CXCR1 and CXCR2 receptors (Gonsiorek et al., 2007). Here we describe its pharmacologic properties at rodent CXCR2 and at the CXCR1 and CXCR2 receptors in the cynomolgus monkey, as well as its in vivo activity in models demonstrating prominent pulmonary neutrophilia, goblet cell hyperplasia, and mucus production. Sch527123 bound with high affinity to the CXCR2 receptors of mouse (K(d) = 0.20 nM), rat (K(d) = 0.20 nM), and cynomolgus monkey (K(d) = 0.08 nM) and was a potent antagonist of CXCR2-mediated chemotaxis (IC(50) approximately 3-6 nM). In contrast, Sch527123 bound to cynomolgus CXCR1 with lesser affinity (K(d) = 41 nM) and weakly inhibited cynomolgus CXCR1-mediated chemotaxis (IC(50) approximately 1000 nM). Oral treatment with Sch527123 blocked pulmonary neutrophilia (ED(50) = 1.2 mg/kg) and goblet cell hyperplasia (32-38% inhibition at 1-3 mg/kg) in mice following the intranasal lipopolysaccharide (LPS) administration. In rats, Sch527123 suppressed the pulmonary neutrophilia (ED(50) = 1.8 mg/kg) and increase in bronchoalveolar lavage (BAL) mucin content (ED(50) =<0.1 mg/kg) induced by intratracheal (i.t.) LPS. Sch527123 also suppressed the pulmonary neutrophilia (ED(50) = 1.3 mg/kg), goblet cell hyperplasia (ED(50) = 0.7 mg/kg), and increase in BAL mucin content (ED(50) = <1 mg/kg) in rats after i.t. administration of vanadium pentoxide. In cynomolgus monkeys, Sch527123 reduced the pulmonary neutrophilia induced by repeat bronchoscopy and lavage (ED(50) = 0.3 mg/kg). Therefore, Sch527123 may offer benefit for the treatment of inflammatory lung disorders in which pulmonary neutrophilia and mucus hypersecretion are important components of the underlying disease pathology.

TLR4 signaling attenuates ongoing allergic inflammation

The relationship between LPS exposure and allergic asthma is poorly understood. Epidemiologic studies in humans have found that exposure to LPS can protect, have no effect, or exacerbate allergic asthma. Similarly, LPS has had variable effects on allergic pulmonary inflammation in the mouse, depending on the model used. In the present study, we studied the effect of very low doses of LPS in models of both short-term and long-term allergen challenge. When challenged with allergen for short periods, wild-type and tlr4-deficient mice had similar responses. However, when challenged for periods of 1 wk or longer, tlr4-deficient mice developed dramatically increased airway eosinophils, serum IgE, and Th2 cytokines compared with similarly challenged, genetically matched C57BL/6 mice. The relative attenuation of allergic responses seen in C57BL/6 mice was dependent on bone marrow-derived cell-specific expression of tlr4, and was not associated with an increase in Th1 responses. The number of dendritic cells in lungs of challenged tlr4-deficient mice was significantly increased compared with those in challenged C57BL/6 mice. No differences were seen in the abilities of naive C57BL/6 and tlr4-deficient mice to develop allergen-specific tolerance after exposure to similar preparations of OVA, suggesting that tolerance and regulation of existing inflammation develop through different mechanisms. The attenuation of eosinophilic inflammation in C57BL/6 mice was abolished when these mice were challenged with OVA supplemented with additional LPS. Together, these findings show that low doses of endotoxin can have regulatory effects on allergic inflammation, particularly in the setting of ongoing allergen exposure.

Cutting Edge: B and T Lymphocyte Attenuator and Programmed Death Receptor-1 Inhibitory Receptors Are Required for Termination of Acute Allergic Airway Inflammation

T cell activation is regulated by coordinate interaction of the T cell Ag receptor and costimulatory signals. Although there is considerable insight into processes that regulate the initiation of inflammation, less is known about the signals that terminate immune responses. We have examined the role of the inhibitory receptors programmed death receptor-1 and B and T lymphocyte attenuator in the regulation of allergic airway inflammation. Our results demonstrate that there is a temporally regulated expression of both the receptors and their ligands during the course of allergic airway inflammation. Following a single inhaled challenge, sensitized wild-type mice exhibit peak inflammation on day 3, which resolves by day 10. In contrast, mice deficient in the expression of programmed death receptor-1 or B and T lymphocyte attenuator have persistent inflammation out to 15 days following challenge. Thus, these receptors are critical determinants of the duration of allergic airway inflammation.

A novel cannabinoid peripheral cannabinoid receptor-selective inverse agonist blocks leukocyte recruitment in vivo

The expression of the cannabinoid peripheral cannabinoid receptor (CB(2)) receptor on peripheral immune cells suggests that compounds specific for CB(2) might be effective anti-inflammatory agents. In this report, we present the initial biological profiling of a novel triaryl bis-sulfone, Sch.336 (N-[1(S)-[4-[[4-methoxy-2-[(4-methoxyphenyl)sulfonyl]phenyl]-sulfonyl]phenyl]ethyl]methanesulfonamide), which is selective for the human cannabinoid CB(2) receptor (hCB(2)). Sch.336 is an inverse agonist at hCB(2), as shown by its ability to decrease guanosine 5'-3-O-(thio)triphosphate (GTPgammaS) binding to membranes containing hCB(2), by the ability of GTPgammaS to left-shift Sch.336 binding to hCB(2) in these membranes, and by the compound's ability to increase forskolin-stimulated cAMP levels in CHO cells expressing hCB(2). In these systems, Sch.336 displays a greater potency than that reported for the CB(2)-selective dihydropyrazole, SR144528 (N-[(1S)-endo-1,3,3-trimethylbicyclo [2.2.1]heptan2-yl]-5-(4-chloro-3-methylphenyl)-1-[(4-methylphenyl)methyl]-1H-pyrazole-3-carboxamide). In vitro, Sch.336 impairs the migration of CB(2)-expressing recombinant cell lines to the cannabinoid agonist 2-arachidonylglycerol. In vivo, the compound impairs migration of cells to cannabinoid agonist HU210 [(6aR)-trans-3-(1,1-dimethylheptyl)-6a,7,10,10a-tetrahydro-1-hydroxy-6,6-dimethyl-6H-dibenzo [b,d] pyran-9-methanol]. Oral administration of the Sch.336 significantly inhibited leukocyte trafficking in several rodent in vivo models, induced either by specific chemokines or by antigen challenge. Finally, oral administration of Sch.336 blocked ovalbumin-induced lung eosinophilia in mice, a disease model for allergic asthma. We conclude that selective cannabinoid CB(2) inverse agonists may serve as novel immunomodulatory agents in the treatment of a broad range of acute and chronic inflammatory disorders in which leukocyte recruitment is a hallmark of disease pathology.

[Regulation of transcription in different HIV-1 subtypes]

Transcriptional activation of HIV-1 gene expression is controlled in part by the interaction of viral and cellular transcription factors with the HIV-1 long terminal repeat (LTR) sequences. LTR variability among different HIV-1 subtypes could affect LTR binding of either cellular or viral elements, influencing the transcription level. This effect, in turn, may have consequences on the biology of the different HIV-1 clades and on disease progression. In some circumstances, a relationship between replication capacity in vitro and changes in binding sequences for transcription factors located at the LTR has been proven.

Vitamin D receptor-deficient mice fail to develop experimental allergic asthma

The active metabolite of vitamin D (1,25-dihydroxyvitamin D(3) (1,25(OH)(2)D(3))) is known to modulate the immune response in Th1 cell-directed diseases. To investigate the role of vitamin D in Th2 cell-directed diseases, experimental allergic asthma was induced in vitamin D receptor (VDR) knockout and in wild-type (WT) mice. As expected, WT mice developed symptoms of airway inflammation with an influx of eosinophils, elevated Th2 cytokine levels, mucous production, and airway hyperresponsiveness. The administration of 1,25(OH)(2)D(3) had no effect on asthma severity. The only discernable effect of 1,25(OH)(2)D(3) on experimental allergic asthma in WT mice was an increased expression of two Th2-related genes (soluble CD23 and GATA-3) in lungs of BALB/c mice exposed to Ag through the nasal route only. By contrast, asthma-induced VDR knockout mice failed to develop airway inflammation, eosinophilia, or airway hyperresponsiveness, despite high IgE concentrations and elevated Th2 cytokines. The data suggest that although 1,25(OH)(2)D(3) induced these Th2-type genes, the treatment failed to have any affect on experimental asthma severity. However, VDR-deficient mice failed to develop experimental allergic asthma, suggesting an important role for the vitamin D endocrine system in the generation of Th2-driven inflammation in the lung.

Blockade of allergic airway inflammation following systemic treatment with a B7-dendritic cell (PD-L2) cross-linking human antibody

We present a novel immunotherapeutic strategy using a human B7-DC cross-linking Ab that prevents lung inflammation, airway obstruction, and hyperreactivity to allergen in a mouse model of allergic inflammatory airway disease. Dendritic cells (DC) have the ability to skew the immune response toward a Th1 or Th2 polarity. The sHIgM12 Ab functions in vitro by cross-linking the costimulatory family molecule B7-DC (PD-L2) on DC up-regulating IL-12 production, homing to lymph nodes, and T cell-activating potential of these APCs. Using chicken OVA as a model Ag, the administration of sHIgM12 Ab to BALB/c mice blocked lung inflammation, airway pathology, and responsiveness to methacholine, even after animals were presensitized and a Th2-polarized immune response was established. This therapeutic strategy was ineffective in STAT4-deficient animals, indicating that IL-12 production is critical in this system. Moreover, the polarity of the immune response upon in vitro restimulation with Ag is changed in wild-type mice, with a resulting decrease in Th2 cytokines IL-4 and IL-5 and an increase in the immunoregulatory cytokine IL-10. These studies demonstrate that the immune response of hypersensitized responders can be modulated using B7-DC cross-linking Abs, preventing allergic airway disease upon re-exposure to allergen.

Requirement for CD28 in the effector phase of allergic airway inflammation

Central to the pathogenesis of allergic airway inflammation are the activation and differentiation of T lymphocytes. This process requires the participation of the CD28 costimulatory receptor. Blockade of CD28 has been demonstrated to prevent inflammation and airway hyperreactivity in a murine model of asthma. Whether this is due specifically to defects in initial T cell activation or whether effector responses are also impaired has not been determined. Using adoptive transfer studies of Ag-specific lymphocytes, we demonstrate that CD28 has a critical role in both the induction and effector phase of allergic airway inflammation. Transfer of in vitro activated and Th2-differentiated Ag-specific lymphocytes from wild-type hosts restored inflammation, but not tissue eosinophilia in CD28-deficient recipients. Furthermore, similarly activated and differentiated CD28-deficient lymphocytes were ineffective at mediating inflammation in wild-type recipients. Secondary cytokine and proliferative responses of activated Th2 cells were highly dependent on CD28 in vitro. Moreover, eosinophil recruitment to both the lung and peritoneum is impaired by the lack of CD28, suggesting a generalized defect in the ability of eosinophils to accumulate at sites of inflammation in vivo. These data identify a novel role for CD28 in the effector phase of allergic airway inflammation and suggest that inhibition of this pathway may be a useful therapeutic intervention in previously sensitized individuals.

Regulation of eosinophilopoiesis in a murine model of asthma

Eosinophilic inflammation plays a key role in tissue damage that characterizes asthma. Eosinophils are produced in bone marrow and recent observations in both mice and humans suggest that allergen exposure results in increased output of eosinophils from hemopoietic tissue in individuals with asthma. However, specific mechanisms that alter eosinophilopoiesis in this disease are poorly understood. The current study used a well-characterized murine animal model of asthma to evaluate alterations of eosinophil and eosinophil progenitor cells (CFU-eo) in mice during initial sensitization to allergen and to determine whether observed changes in either cell population were regulated by T lymphocytes. Following the first intranasal installation of OVA, we observed sequential temporal elevation of eosinophils in bone marrow, blood, and lung. In immunocompetent BALB/c mice, elevation of bone marrow eosinophils was accompanied by transient depletion of CFU-eo in that tissue. CFU-eo rebounded to elevated numbers before returning to normal baseline values following intranasal OVA exposure. In T cell-deficient BALB/c nude (BALB/c(nu/nu)) mice, CFU-eo were markedly elevated following allergen sensitization, in the absence of bone marrow or peripheral blood eosinophilia. These data suggest that eosinophilia of asthma results from alterations in two distinct hemopoietic regulatory mechanisms. Elevation of eosinophil progenitor cells in the bone marrow is T cell independent and likely results from altered bone marrow stromal cell function. Differentiation of eosinophil progenitor cells and phenotypic eosinophilia is T cell dependent and does not occur in athymic nude mice exposed to intranasal allergen.

Attenuation of immunological symptoms of allergic asthma in mice lacking the tyrosine kinase ITK

Allergic asthma patients manifest airway inflammation and some show increases in eosinophils, T(H)2 cells, and cytokines, increased mucous production in the lung, and elevated serum IgE. This T(H)2-type response suggests a prominent role for T(H)2 cells and their cytokines in the pathology of this disease. The Tec family nonreceptor tyrosine kinase inducible T cell kinase (ITK) has been shown to play a role in the differentiation and/or function of T(H)2-type cells, suggesting that ITK may represent a good target for the control of asthma. Using a murine model of allergic asthma, we show here that ITK is involved in the development of immunological symptoms seen in this model. We show that mice lacking ITK have drastically reduced lung inflammation, eosinophil infiltration, and mucous production following induction of allergic asthma. Notably, T cell influx into the lung was reduced in mice lacking ITK. T cells from ITK(-/-) mice also exhibited reduced proliferation and cytokine secretion, in particular IL-5 and IL-13, in response to challenge with the allergen OVA, despite elevated levels of total IgE and increased OVA-specific IgE responses. Our results suggest that the tyrosine kinase ITK preferentially regulates the secretion of the T(H)2 cytokines IL-5 and IL-13 and may be an attractive target for antiasthmatic drugs.

CCR8 is not essential for the development of inflammation in a mouse model of allergic airway disease

Chemokine receptors play an important role in the trafficking of various immune cell types to sites of inflammation. Several chemokine receptors are differentially expressed in Th1 and Th2 effector populations. Th2 cells selectively express CCR3, CCR4, and CCR8, which could direct their trafficking to sites of allergic inflammation. Additionally, increased expression of the CCR8 ligand, TCA-3, has been detected in affected lungs in a mouse model of asthma. In this study, CCR8-deficient mice were generated to address the biological role of CCR8 in a model of allergic airway disease. Using two different protocols of allergen challenge, we demonstrate that absence of CCR8 does not affect the development of pulmonary eosinophilia and Th2 cytokine responses. In addition, administration of anti-TCA-3-neutralizing Ab during allergen sensitization and rechallenge failed to inhibit airway allergic inflammation. These results suggest that CCR8 does not play an essential role in the pathogenesis of inflammation in this mouse model of allergic airway disease.

Using tolerance induced via the anterior chamber of the eye to inhibit Th2-dependent pulmonary pathology

Anterior chamber-associated immune deviation (ACAID), a manifestation of ocular immune privilege, prevents Th1-dependent delayed hypersensitivity from developing in response to eye-derived Ags, thereby preserving vision. Since Th2-type cells have recently been shown to mediate destructive inflammation of the cornea, we wondered whether pre-emptive induction of ACAID could inhibit Th2 responses. Using a murine model of OVA -specific, Th2-dependent pulmonary inflammation, we pretreated susceptible mice by injecting OVA alone into the anterior chamber, or by injecting OVA-pulsed, TGF-beta2-treated peritoneal exudate cells i.v. These mice were then immunized with OVA plus alum strategy that generates Th2-mediated OVA-specific pulmonary pathology. When pretreated mice were challenged intratracheally with OVA, their bronchoalveolar lavage fluids contained far fewer eosinophils and significantly less IL-4, IL-5, and IL-13 compared with that of positive, nonpretreated controls. Similarly, lung-draining lymph node cells of pretreated mice secreted significantly less IL-4, IL-5, and IL-13 when challenged in vitro with OVA. Moreover, sera from pretreated mice contained much lower titers of OVA-specific IgE Abs. We conclude that Ags injected into the anterior chamber of the eye impair both Th1 and Th2 responses. These results reduce the likelihood that ACAID regulates Th1 responses via a Th2-like mechanism. Thus, immune privilege of the eye regulates inflammation secondary to both Th1- and Th2-type immune responses.

Stimulatory effects of B7-related protein-1 on cellular and humoral immune responses in mice

Inducible costimulator (ICOS) and B7-related protein-1 (B7RP-1) constitute a receptor-ligand pair involved in T cell costimulation. In this study, the stimulatory effects of B7RP-1 on cellular and humoral immune responses were investigated giving mice a construct with the extracellular domain of murine B7RP-1 fused with human IgG1 Fc (B7RP-1-Fc). B7RP-1-Fc stimulated contact hypersensitivity (CH) given near either the time of sensitization or challenge with oxazolone. When given near challenge time, B7RP-1-Fc stimulated CH more than a construct containing the extracellular domain of murine B7.2 and Fc (B7.2-Fc). B7RP-1-Fc increased the number of cells in lymph nodes draining the skin sensitized with oxazolone, especially activated T cells. B7RP-1-Fc also increased the ability of the cells in these lymph nodes to induce CH when transfused into naive mice. B7RP-1-Fc stimulated the production of anti-keyhole limpet hemocyanin (KLH) Ab, increasing anti-KLH IgG, IgG2a, and IgE, whereas B7.2-Fc did not affect this production. B7RP-1-Fc also increased the number of cells in lymph nodes draining the skin immunized with KLH and their production of IFN-gamma, IL-4, and IL-10 in response to KLH. Finally, B7RP-1-Fc increased the presence of eosinophils in the bronchoalveolar lavage and lungs of mice sensitized and challenged with OVA so to mount an asthmatic reaction. B7RP-1-Fc stimulates both cellular and humoral immune responses in vivo by increasing number and function of T and B cells reacting to Ag exposure.

CC chemokine receptor-2 is not essential for the development of antigen-induced pulmonary eosinophilia and airway hyperresponsiveness

Monocyte chemoattractant proteins-1 and -5 have been implicated as important mediators of allergic pulmonary inflammation in murine models of asthma. The only identified receptor for these two chemokines to date is the CCR2. To study the role of CCR2 in a murine model of Ag-induced asthma, we compared the pathologic and physiological responses of CCR2(-/-) mice with those of wild-type (WT) littermates following immunization and challenge with OVA. OVA-immunized/OVA-challenged (OVA/OVA) WT and CCR2(-/-) mice developed significant increases in total cells recovered by bronchoalveolar lavage (BAL) compared with their respective OVA-immunized/PBS-challenged (OVA/PBS) control groups. There were no significant differences in BAL cell counts and differentials (i.e., macrophages, PMNs, lymphocytes, and eosinophils) between OVA/OVA WT and CCR2(-/-) mice. Serologic evaluation revealed no significant difference in total IgE and OVA-specific IgE between OVA/OVA WT mice and CCR2(-/-) mice. Lung mRNA expression and BAL cytokine protein levels of IL-4, IL-5, and IFN-gamma were also similar in WT and CCR2(-/-) mice. Finally, OVA/OVA CCR2(-/-) mice developed increased airway hyper-responsiveness to a degree similar to that in WT mice. We conclude that following repeated airway challenges with Ag in sensitized mice, the development of Th2 responses (elevated IgE, pulmonary eosinophilia, and lung cytokine levels of IL-4 and IL5) and the development of airway hyper-responsiveness are not diminished by a deficiency in CCR2.

Role for IgE in airway secretions: IgE immune complexes are more potent inducers than antigen alone of airway inflammation in a murine model

IgE is present in airway secretions from human patients with allergic rhinitis and bronchial asthma. However, the contribution of IgE present locally to the overall airway inflammation is not well understood. We hypothesize that Ag-specific IgE can capture airborne Ags and form immune complexes. These immune complexes may function as potent inducers of immune responses in the lung, contributing to the perpetuation of airway inflammation. BALB/c mice were first sensitized with OVA in alum systemically and then challenged with nebulized OVA. Bronchoalveolar lavage (BAL) fluid from these mice contained significant amounts of IgE, of which >50% was Ag specific. The IgE levels in airway secretions remained elevated for more than 15 days after the termination of Ag exposure. Significant amounts of IgE-OVA immune complexes were detected in BAL fluid from the OVA-challenged mice. For comparison of IgE immune complexes vs Ag alone, we treated OVA-immunized mice with intranasal administration of trinitrophenyl-OVA or trinitrophenyl-OVA-anti-DNP IgE. Those treated with the immune complexes showed significantly higher levels of IL-4 and more pronounced eosinophilia in BAL fluid than did those receiving the Ag alone. The IgE immune complexes did not augment the inflammatory response in high affinity IgE receptor (FcepsilonRI)-deficient mice. We conclude that IgE present in the airways can capture the Ag and that the immune complexes thus formed may augment allergic airway response in an FcepsilonRI-dependent manner. Thus, IgE present in airway secretions may facilitate Ag-mediated allergic airway inflammation.

Naturally occurring human immunodeficiency virus type 1 long terminal repeats have a frequently observed duplication that binds RBF-2 and represses transcription

Approximately 38% of human immunodeficiency virus type 1 (HIV-1)-infected patients within the Vancouver Lymphadenopathy-AIDS Study have proviruses bearing partial 15- to 34-nucleotide duplications upstream of the NF-kappaB binding sites within the 5' long terminal repeat (LTR). This most frequent naturally occurring length polymorphism (MFNLP) of the HIV-1 5' LTR encompasses potential binding sites for several candidate transcription factors, including TCF-1alpha/hLEF, c-Ets, AP-4, and Ras-responsive binding factor 2 (RBF-2) (M. C. Estable et al., J. Virol. 70:4053-4062, 1996). RBF-2 and an apparently related factor, RBF-1, bind to at least four cis elements within the LTR which are required for full transcriptional responsiveness to protein-tyrosine kinases and v-Ras (B. Bell and I. Sadowski, Oncogene 13:2687-2697, 1996). Here we demonstrate that representative MFNLPs from two patients specifically bind RBF-2. In both cases, deletion of the MFNLP caused elevated LTR-directed transcription in cells expressing RBF-2 but not in cells with undetectable RBF-2. RBF-1, but not RBF-2, appears to contain the Ets transcription factor family member GABPalpha/GABPbeta1. Taken together with the fact that every MFNLP from a comparative study of over 500 LTR sequences from 42 patients contains a predicted binding site for RBF-2, our data suggest that the MFNLP is selected in vivo because it provides a duplicated RBF-2 cis element, which may limit transcription in monocytes and activated T cells.

Hepatitis C virus (HCV) specific sequences are demonstrable in the DNA fraction of peripheral blood mononuclear cells from healthy, anti-HCV antibody-negative individuals and cell lines of human origin

No convincing support has been provided so far for the existence of extrahepatic hepatitis C virus particles that should correspond to the sometimes extremely high concentration of 'HCV-RNA' in serum or plasma. If a naturally occurring HCV-specific DNA were to be found, a concept for at least some phenomena in terms of the pathophysiology of HCV should become conceivable. DNA was extracted from peripheral blood mononuclear cells of eleven healthy, anti-HCV-negative individuals, including five long term blood donors, and cells from different cell lines. DNA was subjected to nested polymerase chain reaction omitting a reverse transcriptase step with primers of the 5'NC as well as part of the core region of HCV. Direct polymerase chain reaction, i.e. without a reverse transcriptase step, revealed HCV-specific sequences in the DNA fraction of peripheral blood mononuclear cells of different origin: healthy anti-HCV negative individuals, furthermore in HeLa and MT2 cells. The fragments found were of expected length as well as of shorter and of longer than expected length with respect to the sequence of the HCV genome framed by the primers applied. The results derived from additional hybridization, restriction endonuclase analysis, and sequencing demonstrated HCV-specific sequences in the expected fragments with both a high degree of homology and deletions, respectively, substitutions, as compared to a prototype strain. However, the longer than expected fragments also contained sequences not specific for HCV.

Role of the DIS hairpin in replication of human immunodeficiency virus type 1

The virion-associated genome of human immunodeficiency virus type 1 consists of a noncovalently linked dimer of two identical, unspliced RNA molecules. A hairpin structure within the untranslated leader transcript is postulated to play a role in RNA dimerization through base pairing of the autocomplementary loop sequences. This hairpin motif with the palindromic loop sequence is referred to as the dimer initiation site (DIS), and the type of interaction is termed loop-loop kissing. Detailed phylogenetic analysis of the DIS motifs in different human and simian immunodeficiency viruses revealed conservation of the hairpin structure with a 6-mer palindrome in the loop, despite considerable sequence divergence. This finding supports the loop-loop kissing mechanism. To test this possibility, proviral genomes with mutations in the DIS palindrome were constructed. The appearance of infectious virus upon transfection into SupT1 T cells was delayed for the DIS mutants compared with that obtained by transfection of the wild-type provirus (pLAI), confirming that this RNA motif plays an important role in virus replication. Surprisingly, the RNA genome extracted from mutant virions was found to be fully dimeric and to have a normal thermal stability. These results indicate that the DIS motif is not essential for human immunodeficiency virus type 1 RNA dimerization and suggest that DIS base pairing does not contribute to the stability of the mature RNA dimer. Instead, we measured a reduction in the amount of viral RNA encapsidated in the mutant virions, suggesting a role of the DIS motif in RNA packaging. This result correlates with the idea that the processes of RNA dimerization and packaging are intrinsically linked, and we propose that DIS pairing is a prerequisite for RNA packaging.