Polarization Dependent Scattering in Cavity Optomagnonics

The polarization dependence of magnon-photon scattering in an optical microcavity is reported. Because of the short cavity length, the longitudinal mode-matching conditions found in previously explored, large path-length whispering gallery resonators are absent. Nonetheless, for cross-polarized scattering a strong and broadband suppression of one sideband is observed. This arises due to an interference between the Faraday and second-order Cotton-Mouton effects. To fully account for the suppression of the cross-polarized scattering, it is necessary to consider the squeezing of magnon modes intrinsic to thin-film geometry. A copolarized scattering due to Cotton-Mouton effect is also observed. In addition, the magnon modes involved are identified as Damon-Eshbach surface modes, whose nonreciprocal propagation could be exploited in device applications. This Letter experimentally demonstrates the important role of second-order Cotton-Mouton effect for optomagnonic devices.

Spin Order and Phase Transitions in Chains of Polariton Condensates

We demonstrate that multiply coupled spinor polariton condensates can be optically tuned through a sequence of spin-ordered phases by changing the coupling strength between nearest neighbors. For closed four-condensate chains these phases span from ferromagnetic (FM) to antiferromagnetic (AFM), separated by an unexpected crossover phase. This crossover phase is composed of alternating FM-AFM bonds. For larger eight-condensate chains, we show the critical role of spatial inhomogeneities and demonstrate a scheme to overcome them and prepare any desired spin state. Our observations thus demonstrate a fully controllable nonequilibrium spin lattice.

Triple-Resonant Brillouin Light Scattering in Magneto-Optical Cavities

An enhancement in Brillouin light scattering of optical photons with magnons is demonstrated in magneto-optical whispering gallery mode resonators tuned to a triple-resonance point. This occurs when both the input and output optical modes are resonant with those of the whispering gallery resonator, with a separation given by the ferromagnetic resonance frequency. The identification and excitation of specific optical modes allows us to gain a clear understanding of the mode-matching conditions. A selection rule due to wave vector matching leads to an intrinsic single-sideband excitation. Strong suppression of one sideband is essential for one-to-one frequency mapping in coherent optical-to-microwave conversion.

Phonon-assisted population inversion of a single InGaAs/GaAs quantum dot by pulsed laser excitation

We demonstrate a new method to realize the population inversion of a single InGaAs/GaAs quantum dot excited by a laser pulse tuned within the neutral exciton phonon sideband. In contrast to the conventional method of inverting a two-level system by performing coherent Rabi oscillation, the inversion is achieved by rapid thermalization of the optically dressed states via incoherent phonon-assisted relaxation. A maximum exciton population of 0.67±0.06 is measured for a laser tuned 0.83 meV to higher energy. Furthermore, the phonon sideband is mapped using a two-color pump-probe technique, with its spectral form and magnitude in very good agreement with the result of path-integral calculations.

Optical spin-transfer-torque-driven domain-wall motion in a ferromagnetic semiconductor

We demonstrate optical manipulation of the position of a domain wall in a dilute magnetic semiconductor, GaMnAsP. Two main contributions are identified. First, photocarrier spin exerts a spin-transfer torque on the magnetization via the exchange interaction. The direction of the domain-wall motion can be controlled using the helicity of the laser. Second, the domain wall is attracted to the hot spot generated by the focused laser. Unlike magnetic-field-driven domain-wall depinning, these mechanisms directly drive domain-wall motion, providing an optical tweezerlike ability to position and locally probe domain walls.

Inverse conoscopy: a method to measure polarization using patterns generated by a single birefringent crystal

A method to measure the full polarization vector of a laser beam is proposed and demonstrated. Light is focused onto a birefringent crystal cut such that the slow axis is aligned with the optical axis. The polarization vector of each ray experiences a rotation about the radial axis with a retardation phase dependent on the angle of incidence. Illumination over a wide range of angles applies a range of polarization transforms in parallel that generates a distinct pattern detected by a camera. The input polarization is then inferred from the pattern. The setup uses a single birefringent crystal and involves no moving parts.

Interfacing spins in an InGaAs quantum dot to a semiconductor waveguide circuit using emitted photons

An in-plane spin-photon interface is essential for the integration of quantum dot spins with optical circuits. The optical dipole of a quantum dot lies in the plane and the spin is optically accessed via circularly polarized selection rules. Hence, a single waveguide, which can transport only one in-plane linear polarization component, cannot communicate the spin state between two points on a chip. To overcome this issue, we introduce a spin-photon interface based on two orthogonal waveguides, where the polarization emitted by a quantum dot is mapped to a path-encoded photon. We demonstrate operation by deducing the spin using the interference of in-plane photons. A second device directly maps right and left circular polarizations to antiparallel waveguides, surprising for a nonchiral structure but consistent with an off-center dot.

Coherent optical control of the spin of a single hole in an InAs/GaAs quantum dot

We demonstrate coherent optical control of a single hole spin confined to an InAs/GaAs quantum dot. A superposition of hole-spin states is created by fast (10-100 ps) dissociation of a spin-polarized electron-hole pair. Full control of the hole spin is achieved by combining coherent rotations about two axes: Larmor precession of the hole spin about an external Voigt geometry magnetic field, and rotation about the optical axis due to the geometric phase shift induced by a picosecond laser pulse resonant with the hole-trion transition.

Fast control of nuclear spin polarization in an optically pumped single quantum dot

Highly polarized nuclear spins within a semiconductor quantum dot induce effective magnetic (Overhauser) fields of up to several Tesla acting on the electron spin, or up to a few hundred mT for the hole spin. Recently this has been recognized as a resource for intrinsic control of quantum-dot-based spin quantum bits. However, only static long-lived Overhauser fields could be used. Here we demonstrate fast redirection on the microsecond timescale of Overhauser fields on the order of 0.5 T experienced by a single electron spin in an optically pumped GaAs quantum dot. This has been achieved using coherent control of an ensemble of 10(5) optically polarized nuclear spins by sequences of short radiofrequency pulses. These results open the way to a new class of experiments using radiofrequency techniques to achieve highly correlated nuclear spins in quantum dots, such as adiabatic demagnetization in the rotating frame leading to sub-μK nuclear spin temperatures, rapid adiabatic passage, and spin squeezing.

Phonon-induced Rabi-frequency renormalization of optically driven single InGaAs/GaAs quantum dots

We study optically driven Rabi rotations of a quantum dot exciton transition between 5 and 50 K, and for pulse areas of up to 14π. In a high driving field regime, the decay of the Rabi rotations is nonmonotonic, and the period decreases with pulse area and increases with temperature. By comparing the experiments to a weak-coupling model of the exciton-phonon interaction, we demonstrate that the observed renormalization of the Rabi frequency is induced by fluctuations in the bath of longitudinal acoustic phonons, an effect that is a phonon analogy of the Lamb shift.

Damping of exciton Rabi rotations by acoustic phonons in optically excited InGaAs/GaAs quantum dots

We report experimental evidence identifying acoustic phonons as the principal source of the excitation-induced-dephasing (EID) responsible for the intensity damping of quantum dot excitonic Rabi rotations. The rate of EID is extracted from temperature dependent Rabi rotation measurements of the ground-state excitonic transition, and is found to be in close quantitative agreement with an acoustic-phonon model.

Beating of exciton-dressed states in a single semiconductor InGaAs/GaAs quantum dot

We report picosecond control of excitonic dressed states in a single semiconductor quantum dot. A strong laser pulse couples the exciton and biexciton states, to form an Autler-Townes doublet of the neutral exciton transition. The Rabi-splitting, and hence the admixture of the dressed states follows the envelope of the picosecond control laser. We create a superposition of dressed states, and observe the resulting beat: a direct measurement of a Rabi oscillation in time delay rather than the usual power domain.

Fast optical preparation, control, and readout of a single quantum dot spin

We propose and demonstrate the sequential initialization, optical control, and readout of a single spin trapped in a semiconductor quantum dot. Hole spin preparation is achieved through ionization of a resonantly excited electron-hole pair. Optical control is observed as a coherent Rabi rotation between the hole and charged-exciton states, which is conditional on the initial hole spin state. The spin-selective creation of the charged exciton provides a photocurrent readout of the hole spin state.

A DNA prime-live vaccine boost strategy in mice can augment IFN-gamma responses to mycobacterial antigens but does not increase the protective efficacy of two attenuated strains of Mycobacterium bovis against bovine tuberculosis

The Mycobacterium bovis bacille Calmette-Guérin (BCG) vaccine has variable efficacy for both human and bovine tuberculosis. There is a need for improved vaccines or vaccine strategies for control of these diseases. A recently developed prime-boost strategy was investigated for vaccination against M. bovis infection in mice. BALB/c and C57BL/6 mice were primed with a DNA vaccine, expressing two mycobacterial antigens, ESAT-6 and antigen 85 A and boosted with attenuated M. bovis strains, BCG or WAg520, a newly attenuated strain, prior to aerosol challenge. Before challenge, the antigen-specific production of interferon-gamma (IFN-gamma) was evaluated by ELISPOT and antibody responses were measured. The prime-boost stimulated an increase in the numbers of IFN-gamma producing cells compared with DNA or live vaccination alone, but this varied according to the attenuated vaccine strain, time of challenge and the strain of mouse used. Animals vaccinated with DNA alone generated the strongest antibody response to mycobacterial antigens, which was predominantly IgG1. BCG and WAg520 alone generally gave a 1-2 log10 reduction in bacterial load in lungs or spleen, compared to non-vaccinated or plasmid DNA only control groups. The prime-boost regimen was not more effective than BCG or WAg520 alone. These observations demonstrate the comparable efficacy of BCG and WAg520 in a mouse model of bovine tuberculosis. However, priming with the DNA vaccine and boosting with an attenuated M. bovis vaccine enhanced IFN-gamma immune responses compared to vaccinating with an attenuated M. bovis vaccine alone, but did not increase protection against a virulent M. bovis infection.

IFN-gamma regulates murine interferon-inducible T cell alpha chemokine (I-TAC) expression in dendritic cell lines and during experimental autoimmune encephalomyelitis (EAE)

Murine interferon-inducible T cell alpha chemokine (I-TAC) is a potent non-ELR Cys-X-Cys (CXC) chemokine that predominantly attracts activated T lymphocytes and binds to the receptor CXCR3. Using semiquantitative reverse transcription-polymerase chain reaction (RT-PCR) we analysed murine I-TAC expression in two different progenitor dendritic cell (DC) lines, MTHC-D2 and JAWS II which were exposed to various cytokines, and Con A-activated splenocytes from a panel of knockout mice. Analysis of the progenitor DC lines and Con A cultures demonstrated that murine I-TAC is primarily regulated by interferon (IFN)-gamma via interferon regulatory factor (IRF)-1. It has been proposed that I-TAC may have a role in autoimmune diseases such as multiple sclerosis (MS). Because I-TAC appears to be secreted from antigen-presenting cells (APCs) and attracts activated T cells, we examined the level of murine I-TAC mRNA in the central nervous system (CNS) of wild-type and IFN-gamma-receptor knockout (IFN-gammaR-/-) mice with myelin oligodendrocyte glycoprotein (MOG)35-55 peptide-induced experimental autoimmune encephalomyelitis (EAE). Peak I-TAC expression was detected in wild-type mice on day 14 when the mice begin to recover, whereas very low levels of I-TAC were detected in the CNS of IFN-gammaR-/- mice which develop severe EAE and die. The expression characteristics of murine I-TAC suggest an important mediator of immune cell communication that could augment vaccines and autoimmune therapies.

Cytokines in innate and adaptive immunity

Cytokines and chemokines are hormone-like messengers which act to regulate the development and expression of the broad array of immune responses that are mounted against a variety of pathogens. As such, they are critical determinants of the types of cells which will regulate and participate in innate and adaptive immune responses, they may act both in highly localised environments but also in a systemic manner, and they may, themselves, directly mediate antimicrobial effector activities. In this article, we will outline current concepts of the activities of cytokines and chemokines in the immune response and discuss the various cell types, including dendritic cells and other antigen-presenting cells, T cells and B cells, which both produce and respond to these potent regulatory molecules.

Expression of mouse interleukin-4 by a recombinant ectromelia virus suppresses cytolytic lymphocyte responses and overcomes genetic resistance to mousepox

Genetic resistance to clinical mousepox (ectromelia virus) varies among inbred laboratory mice and is characterized by an effective natural killer (NK) response and the early onset of a strong CD8(+) cytotoxic T-lymphocyte (CTL) response in resistant mice. We have investigated the influence of virus-expressed mouse interleukin-4 (IL-4) on the cell-mediated response during infection. It was observed that expression of IL-4 by a thymidine kinase-positive ectromelia virus suppressed cytolytic responses of NK and CTL and the expression of gamma interferon by the latter. Genetically resistant mice infected with the IL-4-expressing virus developed symptoms of acute mousepox accompanied by high mortality, similar to the disease seen when genetically sensitive mice are infected with the virulent Moscow strain. Strikingly, infection of recently immunized genetically resistant mice with the virus expressing IL-4 also resulted in significant mortality due to fulminant mousepox. These data therefore suggest that virus-encoded IL-4 not only suppresses primary antiviral cell-mediated immune responses but also can inhibit the expression of immune memory responses.

Recombinant adenovirus vectors expressing interleukin-5 and -6 specifically enhance mucosal immunoglobulin A responses in the lung

In this study, we have examined the in vivo effects of interleukin-5 (IL-5) and IL-6 over-expression on systemic and mucosal immune responses using recombinant human type 5 adenoviruses capable of expressing these cytokines upon infection. A recombinant adenovirus containing the murine IL-5 gene within the E3 region was constructed and found to express high levels of IL-5 protein both in vitro and in vivo. Intranasal inoculation of mice with this vector or a vector expressing murine IL-6 increased adenovirus-specific immunoglobulin A (IgA) titres in lung lavage fluid threefold compared with those elicited by control virus. The simultaneous expression of both cytokines by co-inoculation altered the kinetics of the mucosal anti-adenovirus IgA response and resulted in a more than additive increase in antibody titres. The co-expression effect on IgA synthesis was not due to an increase in numbers of antigen-specific resident lung tissue lymphocytes. When mucosal IgG responses were examined, IL-6 expression had the largest impact on anti-adenovirus levels, whereas co-expression produced an intermediate response. Systemic immune responses were also affected by IL-6 expression as a twofold increase in serum IgG anti-adenovirus titres was observed after a secondary challenge with wild-type adenovirus. These results demonstrate a relevant role for IL-5 and IL-6 in the development of mucosal immune responses in vivo and suggest that the incorporation of either IL-5 and/or IL-6 into recombinant adenovirus vectors may be a useful tool in the development of mucosal vaccines.

The effect of IL-5 and eotaxin expression in the lung on eosinophil trafficking and degranulation and the induction of bronchial hyperreactivity

The mechanisms regulating the selective migration and degranulation of eosinophils in the asthmatic lung and the subsequent development of airways hyperreactivity (AHR) have not been fully delineated. In this investigation, we have employed a novel transgene model to facilitate the dissection of the contributions of IL-5 and/or eotaxin to eosinophil function in the absence of complex tissue signals derived from the allergic lung. Gene transfer of IL-5 and/or eotaxin to the lungs of naive mice induced a pronounced and selective airways eosinophilia, but did not result in eosinophil degranulation or AHR. Airways eosinophilia occurred independently of the induction of a blood eosinophilia, but was markedly augmented by the coexpression of both cytokines and/or by the transient mobilization of eosinophils from the bone marrow by the administration of i.v. IL-5. However, for eosinophil degranulation and AHR to occur, the inhalation of Ag was required in association with IL-5 and eotaxin expression. Investigations in IL-5-deficient mice linked eosinophilia, and not solely IL-5 and eotaxin, with the induction of AHR. Furthermore, eosinophil degranulation and AHR were dependent on CD4+ T cells. Importantly, this investigation shows that IL-5 regulates eosinophilia within the lung as well as in the circulation and also amplifies eotaxin-induced chemotaxis in the airway compartment. Moreover, the interplay between these cytokines, CD4+ T cells, and factors generated by Ag inhalation provides fundamental signals for eosinophil degranulation and the induction of AHR.

Genetic vaccination strategies for enhanced cellular, humoral and mucosal immunity

In this article, we describe several novel genetic vaccination strategies designed to facilitate the development of different types of immune responses. These include: i) the consecutive use of DNA and fowlpoxvirus vectors in "prime-boost" strategies which induce greatly enhanced and sustained levels of both cell-mediated immunity and humoral immunity, including mucosal responses; ii) the co-expression of genes encoding cytokines and cell-surface receptors, and the use of immunogenic carrier molecules, for immune modulation and/or improved targeting of vector-expressed vaccine antigens; and iii) the expression of minimal immunogenic amino acid sequences, particularly cytotoxic CD8+ T-cell determinants, in "polytope" vector vaccines. The capacity to modulate and enhance specific immune responses by the use of approaches such as these may underpin the development of vaccines against diseases for which no effective strategies are currently available.

Inhibition of allergic airway inflammation in mice lacking nitric oxide synthase 2

We have used mice rendered deficient for nitric oxide synthase 2 (NOS2) production to study the role of inducible nitric oxide (NO) in the pathogenesis of allergic airways disease. Using a model with OVA as aeroallergen, we show that the manifestations of disease, including infiltration of inflammatory cells, particularly eosinophils, loss of structural integrity of the airway walls, microvascular leakage, pulmonary edema, and airway occlusion are markedly less severe in the NOS2 mutants than in wild-type animals. Indeed, NOS2-deficiency resulted in a 55-60% reduction in both circulatory and pulmonary eosinophil numbers following aeroallergen treatment, although eosinophil maturation or efflux from the bone marrow was not suppressed. There were no obvious differences in levels of airway hyperreactivity recorded in OVA-treated wild-type and NOS2-deficient mice. Interestingly, the suppression of allergic inflammation was accompanied by marked increases in T cell production of IFN-gamma but not by any obvious reduction in the secretion of either IL-4 or IL-5, nor by major changes in the IgG1 and IgE OVA-specific serum Ig profiles in the mutants. The markedly enhanced production of IFN-gamma in NOS2-/- mice was apparently responsible for the suppression of both eosinophilia and disease, as in vivo depletion of this factor restored allergic pathology in these animals. Our data indicate that NOS2 promotes allergic inflammation in airways via down-regulation of IFN-gamma activity and suggest that inhibitors of this molecule may represent a worthwhile therapeutic strategy for allergic diseases including asthma.

Cellular and molecular regulation of eosinophil trafficking to the lung

Airway inflammation is central to the pathogenesis of allergic asthma, and molecules that mediate this process obviously represent targets for therapy. In the present article, we discuss our experiments, which point to CD4+ T cells and IL-5-driven eosinophilia as potential targets for the relief of bronchial hyperreactivity in late-phase asthma.

Cytokine responses in virus infections: effects on pathogenesis, recovery and persistence

During the past year, significant advances have been made in our understanding of cytokine regulation and the respective roles played by T helper cells type 1 and 2 immune responses during virus infection. Numerous mechanisms by which viruses may evade host immune defences have now been identified, some directly influencing cytokine activity. Major advances have also been made in delineating the roles of cytokines and chemokines at different stages in the pathogenesis of HIV infection.

Mucosal IL-12 gene delivery inhibits allergic airways disease and restores local antiviral immunity

Allergic asthma strongly correlates with airways inflammation driven by interleukin (IL)-4 and IL-5 secreted by allergen-specific CD4+ T cells. It is possible that over-production of these factors in the lungs may render asthmatic individuals less able to resolve virus infection of the respiratory tract by down-regulating type 1 cytokine-driven immune responses. IL-12 is important for the establishment of cell-mediated immunity (CMI) and may also inhibit responses driven by type 2 cytokine production. Sustained expression of IL-12 in the airways may, therefore, represent an effective preventive treatment or therapy for allergic asthma and any adverse consequences of excessive production of type 2 cytokines for the development of local CMI. Here, we show that allergic responses in airways profoundly inhibit the development of antiviral CMI in mice following local immunization with vaccinia virus (VV) leading to persistent lung infection. However, mucosal gene transfer of IL-12 in the lung, via a VV vector, inhibited local type 2 cytokine production, both prevented the development of allergic disease and airways hyperreactivity in a manner largely dependent on endogenous interferon-gamma expression and suppressed established allergic disease, and reversed the suppression of local antiviral CMI responses resulting in rapid resolution of virus infection. Our study provides the first direct demonstration that allergic conditions, particularly in airways, may inhibit immune responses to concomitant virus infection and suggests that transient mucosal IL-12 gene therapy represents an effective approach to both the prevention and treatment of allergic airways disease and associated immunosuppression of CMI.

Cytokines and immunity to viral infections

In this review, we discuss two broad approaches we have taken to study the role of cytokines and chemokines in antiviral immunity. Firstly, recombinant vaccinia viruses were engineered to express genes encoding cytokines and chemokines of interest. Potent antiviral activity was mediated by many of these encoded factors, including IL-2, IL-12, IFN-gamma, TNF-alpha, CD40L, Mig and Crg-2. In some cases, host defense mechanisms were induced (IL-2, IL-12, Mig and Crg-2), whilst for others, a direct antiviral effect was demonstrated (IFN-gamma, TNF-alpha and CD40L). In sharp contrast, vector-directed expression of IL-4, a type 2 factor, greatly increased virus virulence, due to a downregulation of host type 1 immune responses. Our second experimental approach involved the use of strains of mice deficient for the production of particular cytokines or their receptors, often in combination with our engineered viruses. Mice deficient in either IFN-gamma, IFN-gamma R, IFN-alpha/beta R, TNFRs, CD40 or IL-6 were, in general, highly susceptible to poxvirus infection. Surprisingly, not only the TNFR1, but also the TNFR2, was able to mediate the antiviral effects of TNF-alpha in vivo, whilst the antiviral activity observed following CD40-CD40L interaction is a newly defined function which may involve apoptosis of infected cells. Through the use of perforin-deficient mice, we were able to demonstrate a requirement for this molecule in the clearance of some viruses, such as ectromelia virus, whilst for others, such as vaccinia virus, perforin was less important but IFN-gamma was essential.

DNA vaccination against virus infection and enhancement of antiviral immunity following consecutive immunization with DNA and viral vectors

Recent demonstrations of the immunogenicity of antigens encoded in DNA plasmids following delivery by various routes have heralded a new era in vaccine development. In this article, we review progress in DNA-based antiviral immunoprophylaxis. Preclinical studies have already established the immunogenicity of DNA plasmids encoding protective antigens from a wide variety of viral pathogens and work published in recent months has raised real prospects of broadly protective DNA vaccination against infections with influenza virus and HIV. We also describe a consecutive immunization protocol consisting of a priming dose of vaccine antigen encoded in DNA plasmids followed by a booster with the same antigen encoded in recombinant fowlpox virus vectors. We have used this strategy to generate protective antiviral cell-mediated immunity and sustained, high-level antibody responses both systemically and at mucosae, and to elucidate immunological mechanisms underlying the development of immunity to antigens delivered in DNA vectors.

DNA immunization

DNA immunization has recently emerged as a highly promising approach for the prevention and therapy of a wide range of infectious and non-infectious diseases. Here, we review the rapid development of this field and recent advances in our understanding of some of the mechanisms by which DNA vaccines stimulate the immune system.

Aeroallergen-induced eosinophilic inflammation, lung damage, and airways hyperreactivity in mice can occur independently of IL-4 and allergen-specific immunoglobulins

In this investigation we have used a mouse model containing certain phenotypic characteristics consistent with asthma and IL-4- and CD40-deficient mice to establish the role of this cytokine and allergen-specific immunoglobulins in the initiation of airways hyperreactivity and morphological changes to the airways in responses to aeroallergen challenge. Sensitization and aerosol challenge of mice with ovalbumin resulted in a severe airways inflammatory response which directly correlated with the induction of extensive airways damage and airways hyperreactivity to beta-methacholine. Inflammatory infiltrates were primarily characterized by the presence of CD4+ T cells and eosinophils. In IL-4-deficient mice, the recruitment of airways eosinophils was impaired, but not abolished in response to aeroallergen. Moreover, the characteristic airways damage and hyperreactivity normally resulting from allergen inhalation were not attenuated. Induction of these structural and functional changes to the airways occurred in the absence of ovalbumin-specific IgE and IgG1, but IgG2a and IgG3 were detected in the sera of IL-4-deficient mice. CD4+ T cells isolated from both wild-type and IL-4-deficient mice given ovalbumin produced significant levels of IL-5 after in vitro stimulation. Treatment of IL-4-deficient mice with anti-IL-5 mAb before aeroallergen challenge abolished blood and airways eosinophilia, lung damage, and airways hyperreactivity. These results indicate that IL-4 is not essential for the development of IL-5-producing CD4+ T cells or for the induction of eosinophilic inflammation and airways damage and hyperreactivity. In response to sensitization and aerosol challenge, CD40-deficient mice did not produce ovalbumin-specific IgE, IgG isotypes, or IgA, and airways inflammation and hyperreactivity were not attenuated. Our results suggest that allergic airways disease can occur via pathways which operate independently of IL-4 and allergen-specific immunoglobulins. Activation of these pathways is intimately associated with IL-5 and eosinophilic inflammation. Such pathways may play a substantive role in the etiology of asthma.

Eosinophils are not required for the rejection of neovascularized fetal pig proislet xenografts in mice

The rejection of neovascularized pig proislet (islet precursor) xenografts in mice is a CD4 T cell-dependent process involving invasion of the graft site mainly by host CD4 T cells and eosinophils. We previously identified CD4 T cell-dependent enhancement of intragraft IL-3, IL-4, and IL-5 mRNA expression during acute xeno-rejection in CBA/H recipient mice. In the present study we investigated the role of each cytokine and the involvement of eosinophils in the rejection of pig proislet xenografts using cytokine gene knockout mice (IL-4 -/- and IL-5 -/-) and the treatment of transplant recipients with anti-IL-3 mAb. In IL-4 -/- mice, IL-5 -/- recipient animals, and anti-IL-3 mAb-treated CBA/H mice, eosinophil accumulation at the transplant site was inhibited or ablated, but the kinetics of xenograft rejection was unaltered. Prolonged xenograft survival was only achieved in anti-CD4 mAb-treated mice and consistently correlated with the absence of intragraft IL-3, IL-4, and IL-5 mRNA enhancement. Together these findings indicate that neither IL-3, nor IL-4, nor IL-5 individually plays an obligatory role in the rejection process. The cytokine mRNA profile correlating with the lack of eosinophil recruitment was variable; the data suggest that IL-4 regulates eosinophil involvement in the xeno-rejection reaction indirectly via effects on IL-5 and IL-3 transcript expression. There is also suggestive evidence that IL-5 may influence IL-3 and IL-4 mRNA expression via feedback inhibition. Eosinophils, therefore, do not play an essential role in the rejection of neovascularized pig proislet xenografts in mice.

Eosinophils are not required for the rejection of neovascularized fetal pig proislet xenografts in mice

The rejection of neovascularized pig proislet (islet precursor) xenografts in mice is a CD4 T cell-dependent process involving invasion of the graft site mainly by host CD4 T cells and eosinophils. We previously identified CD4 T cell-dependent enhancement of intragraft IL-3, IL-4, and IL-5 mRNA expression during acute xeno-rejection in CBA/H recipient mice. In the present study we investigated the role of each cytokine and the involvement of eosinophils in the rejection of pig proislet xenografts using cytokine gene knockout mice (IL-4 -/- and IL-5 -/-) and the treatment of transplant recipients with anti-IL-3 mAb. In IL-4 -/- mice, IL-5 -/- recipient animals, and anti-IL-3 mAb-treated CBA/H mice, eosinophil accumulation at the transplant site was inhibited or ablated, but the kinetics of xenograft rejection was unaltered. Prolonged xenograft survival was only achieved in anti-CD4 mAb-treated mice and consistently correlated with the absence of intragraft IL-3, IL-4, and IL-5 mRNA enhancement. Together these findings indicate that neither IL-3, nor IL-4, nor IL-5 individually plays an obligatory role in the rejection process. The cytokine mRNA profile correlating with the lack of eosinophil recruitment was variable; the data suggest that IL-4 regulates eosinophil involvement in the xeno-rejection reaction indirectly via effects on IL-5 and IL-3 transcript expression. There is also suggestive evidence that IL-5 may influence IL-3 and IL-4 mRNA expression via feedback inhibition. Eosinophils, therefore, do not play an essential role in the rejection of neovascularized pig proislet xenografts in mice.

Interleukin-7 enhances cell-mediated immune responses in vivo in an interleukin-2-dependent manner

We have engineered recombinant vaccinia virus vectors expressing murine interleukin-7 (IL-7) in order to study the activity of this factor during virus infection. Virus-encoded IL-7 dramatically increased splenic cellularity in infected mice and enhanced the proliferative activity of T cells and their capacity to secrete IL-2 and IL-6, but not IFN-gamma, TNF-alpha or IL-4. Numbers of splenic CD4+ and CD8+ T lymphocytes were elevated two- to threefold. IL-7 also mediated a marked enhancement of both antigen-specific and nonspecific cellular immune activity. Total splenic antiviral cytotoxic T cells (CTL), natural killer (NK), and lymphokine-activated killer cells (LAK) responses were augmented significantly in mice given VV-HA-IL-7 compared with those given control virus, with accelerated clearance of the former. The enhanced antiviral cellular immune activity mediated by IL-7 was critically dependent on IL-2 produced by the host, but occurred independently of IFN-gamma. The ability of IL-7 to induce cellular immune responses in vivo may have applications in antiviral immunotherapy, particularly in cases of immunodeficiency.

Cytokine enhancement of immune responses important for immunocontraception

To be effective, an immunocontraceptive vaccine should elicit strong, sustained antibody responses. Circulating antibodies may block the function of hormones and target some gamete antigens, but the most effective inhibition of fertilization will probably be achieved by antibodies in the reproductive tract. It may also be beneficial to administer vaccine antigens with strong adjuvants, such as cytokines, in order to achieve high specific antibody titres. In this review recent findings concerning the role of cytokines in the regulation of antibody responses, particularly at mucosae, are described and prospects for immunization for immune responses which may be important for fertility control are discussed. On the basis of these findings, a model system for the delivery of vaccine antigens to the immune system in vaccinia, fowlpox or DNA plasmid vectors along with type-2 cytokines, such as interleukin-4 (IL-4), IL-5 and IL-6, as B cell adjuvants is presented. Studies such as these in the areas of antigen delivery and enhancement of immune responses are aimed at providing new options for fertility control, particularly via oral vaccination.

Interleukin-4 mediates down regulation of antiviral cytokine expression and cytotoxic T-lymphocyte responses and exacerbates vaccinia virus infection in vivo

Interleukin-4 (IL-4) promotes the growth of Th2-type cells while down regulating the development of Th1-type cells. It has been suggested that the actions of this factor inhibit Th1-type effector activity in vivo and may underlie the development of diseases normally controlled by cell-mediated immune responses. Here, we show that clearance of recombinant vaccinia viruses (VV) engineered to express the gene for murine IL-4 is markedly delayed in mice compared with control recombinant VV. While antiviral antibody levels and NK activity in mice given control virus or IL-4-expressing virus were similar, antiviral cytotoxic T-lymphocyte responses were profoundly suppressed throughout the course of infection with the latter. Limiting dilution analysis of IL-4-virus-infected spleens revealed a marked reduction in numbers of cytotoxic T-lymphocyte precursors. Furthermore, reverse transcriptase PCR analysis of splenic mRNA prepared from mice infected with the IL-4-expressing VV showed a marked down regulation of IL-12, gamma interferon, and IL-2 gene expression compared with that from mice given control virus. IL-4 also inhibited the production of nitric oxide (NO), a potent mediator of antimicrobial activity. Together, these data show that IL-4 markedly suppresses the development of antiviral cell-mediated immune responses in vivo with deleterious effects on virus clearance.

Antigen delivery strategies for mucosal vaccines

Progress towards effective vaccines to control internal parasites, especially those affecting mucosal compartments, has been inhibited by the combined problems of the antigenic complexity of parasites and the lack of understanding of the host response. However, the accumulation of information regarding regulation of mucosal immunity has enabled a reappraisal of vaccination options to provide appropriate mucosal effector responses. The pivotal role of T cell influences, and in particular the contribution of cytokine signals, has been clearly established from in vitro studies, but data emerging from our laboratories provide evidence for these effects in vivo. We have demonstrated the role of T cells in determining the outcome of an intestinal response and propose a role for local Th2 cytokine production in this regard. To support this proposition, the distribution of cytokine mRNA has been determined by in situ hybridisation techniques in normal and parasitised animals. Further, we have shown that in the absence of Th2 cytokines (using gene knockout animals) mucosal responses are grossly deficient; we have also shown that this defect can be overcome by vector-directed gene therapy. These studies have indicated that new mucosal immunisation opportunities exist by combining traditional immunisation approaches with strategies to upregulate local cytokine production. However, the success of these new strategies will depend on selection of highly immunogenic subunit antigens, coupled with techniques for cytokine manipulation and delivery with appropriate adjuvant/vehicle formulations. This paper reviews delivery technologies available to chaperone labile antigenic and genetic material to appropriate sites for mucosal stimulation after systemic or oral administration.

Studies of immunity and bacterial invasiveness in mice given a recombinant salmonella vector encoding murine interleukin-6

Interleukin-6 (IL-6) was expressed in Salmonella typhimurium in an attempt to increase the mucosal immune response against the bacterium. Murine IL-6 was PCR amplified from cDNA, cloned, sequenced, and found to be functionally active when expressed in S. typhimurium BRD509, the (delta)aroA (delta)aroD vaccine strain. Expression of murine IL-6 did not appear to adversely affect the growth of salmonellae, as the construct was retained in the absence of antibiotic selection and the growth rate was unaffected compared with that of the parent strain in vitro. However, IL-6 expression led to a significant reduction in bacterial invasiveness in vitro and in vivo. Splenocytes and small intestinal lamina propria lymphocytes were isolated from mice orally immunized with BRD509 expressing IL-6 (pKK233-2/IL-6), and the number of antibody-secreting cells was determined by the ELISPOT technique. No differences were observed between mice immunized with BRD509(pKK.233-2/IL-6) and those immunized with BRD509(pKK233-2) with respect to the antibody subclass-specific responses elicited despite the markedly reduced invasiveness of the former. Serum antibody responses were also examined by a kinetic enzyme-linked immunosorbent assay (ELISA), and equivalent levels of antibody response were detected in mice given BRD509(pKK233-2/IL-6) and those given BRD509(pKK233-2). The humoral immune response against bacterial lipopolysaccharides was also examined in transgenic IL-6-deficient mice given oral inocula of BRD509. Equivalent numbers of antibody-secreting cells (ELISPOTs) were observed in the spleens and laminae propriae of both IL-6-deficient (-/-) mice and control (+/+) mice harboring an intact IL-6 gene, whereas small, yet significant differences in the serum immunoglobulin A ELISA titers were observed. These data suggest that the immunoglobulin A response against Salmonella lipopolysaccharides is largely IL-6 independent.

IL-5-deficient mice have a developmental defect in CD5+ B-1 cells and lack eosinophilia but have normal antibody and cytotoxic T cell responses

Mice deficient in interleukin-5 (IL-5-/- mice) were generated by gene targeting in embryonal stem cells. Contrary to previous studies, no obligatory role for IL-5 was demonstrated in the regulation of conventional B (B-2) cells, in normal T cell-dependent antibody responses or in cytotoxic T cell development. However, CD5+ B cells (B-1 cells) in the peritoneal cavity were reduced by 50%-80% in 2-week-old IL-5-/- mice, returning to normal by 6-8 weeks of age. The IL-5-/- mice did not develop blood and tissue eosinophilia when infected with the helminth Mesocestoides corti, but basal levels of eosinophils with normal morphology were produced in the absence of IL-5. IL-5 deficiency did not affect the worm burden of infected mice, indicating that increased eosinophils do not play a significant role in the host defence in this parasite model.

Interleukin 5 deficiency abolishes eosinophilia, airways hyperreactivity, and lung damage in a mouse asthma model

Airways inflammation is thought to play a central role in the pathogenesis of asthma. However, the precise role that individual inflammatory cells and mediators play in the development of airways hyperreactivity and the morphological changes of the lung during allergic pulmonary inflammation is unknown. In this investigation we have used a mouse model of allergic pulmonary inflammation and interleukin (IL) 5-deficient mice to establish the essential role of this cytokine and eosinophils in the initiation of aeroallergen-induced lung damage and the development of airways hyperreactivity. Sensitization and aerosol challenge of mice with ovalbumin results in airways eosinophilia and extensive lung damage analogous to that seen in asthma. Aeroallergen-challenged mice also display airways hyperreactivity to beta-methacholine. In IL-5-deficient mice, the eosinophilia, lung damage, and airways hyperreactivity normally resulting from aeroallergen challenge were abolished. Reconstitution of IL-5 production with recombinant vaccinia viruses engineered to express this factor completely restored aeroallergen-induced eosinophilia and airways dysfunction. These results indicate that IL-5 and eosinophils are central mediators in the pathogenesis of allergic lung disease.

Genetic approaches to the study of cytokine regulation of mucosal immunity

Efforts to design effective mucosal vaccines have been hampered by an incomplete understanding of factors controlling the development of mucosal immunity. It is now clear, however, that T cell-derived cytokines play a major role. Recent developments in 'gene knockout' technology have allowed the generation of strains of mice in which particular genes have been inactivated. The availability of mice rendered deficient for production of Th2 cytokines has facilitated studies of the induction and development of mucosal immune responses in the absence of these factors. We have used several genetic approaches, including cytokine-deficient mice and recombinant vectors constructed to express genes for a range of different cytokines, to demonstrate the importance of these factors in the mucosa. Such genetic approaches appear to represent powerful tools for in vivo studies of the influence of cytokines in mucosal immunoregulation.

IgA production by peritoneal cavity B cells is IL-6 independent: implications for intestinal IgA responses

We have shown previously both in vitro and in vivo that IL-6 is an important factor for the development of IgA-producing B cells. However, despite the lack of this cytokine in mice with targeted disruption of the interleukin (IL)-6 gene (gene knockout mice), a substantial number of IgA-producing plasma cells occur in their intestinal mucosa. The experiments reported here indicate that there is a population of IgA-producing B cell precursors originating from the peritoneal cavity, distinguished from conventional Peyer's patch-derived precursors by their expression of CD5, and that IgA secretion by these cells is IL-6-independent. Further, there is an increase in CD5 expression among brightly staining IgA-producing cells obtained from the intestinal lamina propria of IL-6 gene-disrupted mice compared to normal controls. These data suggest an explanation for the persistence of IgA-producing plasma cells in the intestinal mucosa of IL-6-depleted mice and indicate the importance of IL-6 for development of conventional precursors of IgA-producing B cells, but not those derived from the peritoneal cavity pool.

Selective induction of immune responses by cytokines coexpressed in recombinant fowlpox virus

Avipoxviruses have recently been studied as potential vectors for the delivery of heterologous vaccine antigen. Because these viruses abortively infect mammalian cells yet still effectively present encoded foreign genes to the host immune system, they offer a safer but effective alternative to other live virus vectors. We have examined the effect of coexpressing the cytokine interleukin-6 or gamma interferon on immune responses to a recombinant fowlpox virus expressing influenza virus hemagglutinin. The encoded cytokine was expressed for prolonged periods in infected cell culture with little cytopathic effect due to the abortive nature of the infection. In mice, vector-expressed cytokine dramatically altered immune responses induced by the coexpressed hemagglutinin antigen. Expression of interleukin-6 augmented both primary systemic and mucosal antibody responses and primed for enhanced recall responses. In contrast, expression of gamma interferon markedly inhibited antibody responses without affecting the generation of cell-mediated immunity. The safety of these constructs was demonstrated in mice with severe combined immunodeficiency, and no side effects due to cytokine expression were observed. In summary, fowlpox virus vectors encoding cytokines represent a safe and effective vaccine strategy which may be used to selectively manipulate the immune response.

The role of interleukin-6 in mucosal IgA antibody responses in vivo

In mice with targeted disruption of the gene that encodes interleukin-6 (IL-6), greatly reduced numbers of immunoglobulin A (IgA)-producing cells were observed at mucosae and grossly deficient local antibody responses were recorded after mucosal challenge with either ovalbumin or vaccinia virus. The IgA response in the lungs was completely restored after intranasal infection with recombinant vaccinia viruses engineered to express IL-6. These findings demonstrate a critical role for IL-6 in vivo in the development of local IgA antibody responses and illustrate the effectiveness of vector-directed cytokine gene therapy.

Cytokine regulation of mucosal responses: a rational basis for new vaccine delivery strategies

In this review, cytokine regulation of mucosal responses is discussed in relation to the mucosal immune network and regulation of IgA responses. Based on this understanding, aspects of gene therapy for manipulation of the host environment and vaccine delivery systems are discussed. Although evidence obtained in vitro is briefly reviewed the general focus of this article is on evidence obtained from models in vivo.

Enhancement of mucosal IgA responses by interleukins 5 and 6 encoded in recombinant vaccine vectors

The expression of the genes for murine interleukin-5 (IL-5) or IL-6 in recombinant vaccinia virus vectors markedly increased IgA reactivity to co-expressed heterologous antigen in the lungs of mice inoculated intranasally with the viruses. These elevated local IgA responses reached a peak four times higher than those elicited by control viruses 14 days after infection and these peak levels were maintained for at least four weeks. Elevated IgA responses, reaching a peak 3-4 weeks after immunization, were also observed in the lungs of mice inoculated with IL-6 expressed by another vector, fowlpox virus. The results indicate that these factors enhance the development of mucosal IgA reactivity in vivo and suggest that their expression in mucosal vaccine vectors may stimulate local immune responses. The approach described in this study may be useful in stimulating mucosal immunity to a wide range of vector-encoded antigens, not only for vaccination against disease but also for immunocontraception by the co-expression of antigens involved in reproduction.

Interleukin-5 expressed by a recombinant virus vector enhances specific mucosal IgA responses in vivo

Several in vitro studies have shown that murine interleukin-5 (mIL-5) enhances IgA production by activated mucosal B cells. To date, however, there is no evidence that this factor significantly up-regulates mucosal IgA responses in vivo. Here, we show that expression of the gene for mIL-5 in a recombinant vaccinia virus vector markedly increases IgA responses to co-expressed heterologous antigen in the lungs of mice given intranasal inocula of the virus. The elevated local IgA responses to vectors expressing mIL-5 peaked at a fourfold higher level than those elicited by control virus at 14 days after infection and were sustained for at least 4 weeks. Increased IgA responses were abrogated in mice treated with monoclonal antibody against mIL-5 and were not detected in systemic lymphoid tissue. No enhancement of specific IgG levels was found either locally or systemically. Our results indicate that mIL-5 selectively enhances the development of mucosal IgA responses in vivo and suggest that expression of this factor in mucosal vaccine vectors may stimulate local immune reactivity.

A case for cytokines as effector molecules in the resolution of virus infection

Some cytokines are known to have potent antiviral activity in vitro, and recent work shows that severely immunodeficient mice, which lack conventional effector T cells, can still recover from virus infection provided these factors are present at sites of virus replication. Here Alistair Ramsay, Janet Ruby and Ian Ramshaw discuss these findings and raise fundamental questions concerning the physiological role of cytotoxic T cells in the resolution of virus infection.

Recombinant vaccine vector-induced protection of athymic, nude mice from influenza A virus infection. Analysis of protective mechanisms

Athymic, nude mice, which normally succumb to virus infection, can resolve infection with recombinant vaccinia virus (rVV) engineered to express IL-2. We have demonstrated that interferon-gamma (IFN-gamma) produced by natural killer (NK) cells and other immunocytes in response to the virus-encoded interleukin-2 (IL-2) is crucial to recovery. Here, we extend this work to show that nude mice, when primed intravenously with rVV co-expressing both IL-2 and an influenza virus haemagglutinin (HA) gene, are also protected following challenge with a lethal dose of homologous influenza virus. A substantial increase in the number of influenza virus-reactive antibody-secreting cells producing antibody of the IgM isotype, but not of the IgG or IgA isotypes, was found in spleens and lungs of the protected mice. Treatment with monoclonal antibodies to IFN-gamma or to the NK marker, as GM1, at challenge and thereafter, led to their death however, though the specific IgM antibody response was unaffected. These data suggest that both specific antibody and non-specific antiviral reactivity are important elements of the protective response and show that this immunization strategy may be used to protect severely immunocompromised individuals.