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Suryaprakash Sambhara

Publications and source records attributed to Suryaprakash Sambhara.

11 recordsLinked to original sources
PubMed2006

Role of host cytokine responses in the pathogenesis of avian H5N1 influenza viruses in mice.

Highly pathogenic avian H5N1 influenza viruses are now widespread in poultry in Asia and have recently spread to some African and European countries. Interspecies transmission of these viruses to humans poses a major threat to public health. To better understand the basis of pathogenesis of H5N1 viruses, we have investigated the role of proinflammatory cytokines in transgenic mice deficient in interleukin-6 (IL-6), macrophage inflammatory protein 1 alpha (MIP-1alpha), IL-1 receptor (IL-1R), or tumor necrosis factor receptor 1 (TNFR1) by the use of two avian influenza A viruses isolated from humans, A/Hong Kong/483/97 (HK/483) and A/Hong Kong/486/97 (HK/486), which exhibit high and low lethality in mice, respectively. The course of disease and the extent of virus replication and spread in IL-6- and MIP-1alpha-deficient mice were not different from those observed in wild-type mice during acute infection with 1,000 50% mouse infective doses of either H5N1 virus. However, with HK/486 virus, IL-1R-deficient mice exhibited heightened morbidity and mortality due to infection, whereas no such differences were observed with the more virulent HK/483 virus. Furthermore, TNFR1-deficient mice exhibited significantly reduced morbidity following challenge with either H5N1 virus but no difference in viral replication and spread or ultimate disease outcome compared with wild-type mice. These results suggest that TNF-alpha may contribute to morbidity during H5N1 influenza virus infection, while IL-1 may be important for effective virus clearance in nonlethal H5N1 disease.

Animals↗
PubMed2006

NS1 protein of influenza A virus inhibits the function of intracytoplasmic pathogen sensor, RIG-I.

Retinoic acid-inducible gene I (RIG-I) has recently been identified as one of the key intracellular sensors of virus infection. RIG-I binds to cytosolic double-stranded RNA and initiates a signaling cascade that leads to the activation of transcription factors required for expression of type I interferon (IFN-I). Previous evidence suggests that nonstructural protein 1 (NS1) encoded by influenza A virus (IAV) suppresses IFN-I secretion in virus-infected cells by an unknown mechanism. In the present study, we demonstrate that RIG-I is required for induction of IFN-I in an IAV-infected human lung epithelial cell line. Knockdown of RIG-I expression by RNA interference greatly impairs production of IFN-beta in cells infected with different strains of wild-type IAV. Furthermore, co-expression of IAV NS1 down-regulates production of IFN-beta induced by RIG-I agonists, and ectopic expression of RIG-I inhibits the replication of IAV. These results provide further information on the mechanism by which IAV NS1 antagonizes the host antiviral response.

Cytoplasm↗
PubMed2006

Development of adenoviral-vector-based pandemic influenza vaccine against antigenically distinct human H5N1 strains in mice.

INTRODUCTION: Avian H5N1 influenza viruses currently circulating in southeast Asia could potentially cause the next pandemic. However, currently licensed human vaccines are subtype-specific and do not protect against these H5N1 viruses. We aimed to develop an influenza vaccine and assessed its immunogenicity and efficacy to confer protection in BALB/c mice. METHODS: We developed an egg-independent strategy to combat the avian influenza virus, because the virus is highly lethal to chickens and the maintenance of a constant supply of embryonated eggs would be difficult in a pandemic. We used a replication-incompetent, human adenoviral-vector-based, haemagglutinin subtype 5 influenza vaccine (HAd-H5HA), which induces both humoral and cell-mediated immune responses against avian H5N1 influenza viruses isolated from people. FINDINGS: Immunisation of mice with HAd-H5HA provided effective protection from H5N1 disease, death, and primary viral replication (p<0.0001) against antigenically distinct strains of H5N1 influenza viruses. Unlike the recombinant H5HA vaccine, which is based on a traditional subunit vaccine approach, HAd-H5HA vaccine induced a three-fold to eight-fold increase in HA-518-epitope-specific interferon-gamma-secreting CD8 T cells (p=0.01). INTERPRETATION: Our findings highlight the potential of an Ad-vector-based delivery system, which is both egg-independent and adjuvant-independent and offers stockpiling options for the development of a pandemic influenza vaccine.

Animals↗
PubMed2005

A distal regulatory region is required for constitutive and IFN-beta-induced expression of murine TLR9 gene.

TLR9 is critical for the recognition of unmethylated CpG DNA in innate immunity. Accumulating evidence suggests distinct patterns of TLR9 expression in various types of cells. However, the molecular mechanism of TLR9 expression has received little attention. In the present study, we demonstrate that transcription of murine TLR9 is induced by IFN-beta in peritoneal macrophages and a murine macrophage cell line RAW264.7. TLR9 is regulated through two cis-acting regions, a distal regulatory region (DRR) and a proximal promoter region (PPR), which are separated by approximately 2.3 kbp of DNA. Two IFN-stimulated response element/IFN regulatory factor-element (ISRE/IRF-E) sites, ISRE/IRF-E1 and ISRE/IRF-E2, at the DRR and one AP-1 site at the PPR are required for constitutive expression of TLR9, while only the ISRE/IRF-E1 motif is essential for IFN-beta induction. In vivo genomic footprint assays revealed constitutive factor occupancy at the DRR and the PPR and an IFN-beta-induced occupancy only at the DRR. IRF-2 constitutively binds to the two ISRE/IRF-E sites at the DRR, while IRF-1 and STAT1 are induced to bind to the two ISRE/IRF-E sites and the ISRE/IRF-E1, respectively, only after IFN-beta treatment. AP-1 subunits, c-Jun and c-Fos, were responsible for the constitutive occupancy at the proximal region. Induction of TLR9 by IFN-beta was absent in STAT1-/- macrophages, while the level of TLR9 induction was decreased in IRF-1-/- cells. This study illustrates the crucial roles for AP-1, IRF-1, IRF-2, and STAT1 in the regulation of murine TLR9 expression.

Amino Acid Sequence↗
PubMed2004

Impaired antigen-induced CD8+ T cell clonal expansion in aging is due to defects in antigen presenting cell function.

CD8+ T cell activation depends on interaction with antigen-presenting cells (APCs) and this interaction leads to the expansion of T cells with the capacity to control infection. Using professional APCs, we demonstrate that with age, the duration of APC-T cell contact time required to achieve clonal expansion increases. Naïve CD8+ T cells from aged mice showed no defect in antigen-induced proliferation when stimulated with APC from young mice. In contrast, CD8+ T cells from young mice exhibited reduced clonal expansion and secreted significantly lower amounts of IFN-gamma when stimulated by APCs from aged mice. The aged APCs were defective in costimulatory molecule expression and cytokine and chemokine secretion. These data indicate that defects in APC function lead to poor T cell clonal expansion and function in aging.

Animals↗
PubMed2004

Innate immunity in aging: impact on macrophage function.

Innate and adaptive immune functions decline with age, leading to increased susceptibility to infectious diseases and cancer, and reduced responses to preventive vaccination in the elderly population. Macrophages function as 'pathogen sensors' and play an important role in the initiation of inflammatory responses, elimination of pathogens, manipulation of the adaptive immune response and reparation of damaged tissue. In this paper, we review the literature addressing the impact of aging on the macrophage population.

Aging↗
PubMed2004

Immunity to influenza: the challenges of protecting an aging population.

Influenza viruses cause annual epidemics and occasional pandemics of acute respiratory disease. Improved vaccines that can overcome the decline in immune function with aging and/or can induce broader immunity to novel pandemic strains are a high priority. To design improved vaccines for the elderly, we need to better understand the effects of age on both innate and adaptive immunity. In a murine model, we have determined that defects in antigen-presenting cell (APC) expression of pattern-recognition molecules, co-stimulatory molecules, and cytokine production may play an important role in the reduced clonal expansion of T cells in aging. The use of immunomodulators such as adjuvants may overcome some of the defects of aging immunity and may also be useful in the development of improved vaccines for avian influenza A subtypes that pose a pandemic threat. Several novel strategies including the use of ISCOM-formulated vaccines, mucosal delivery, or DNA vaccination provided cross-subtype protection that could provide an important component of immunity in the event of a pandemic.

Adjuvants, Immunologic↗
PubMed2003

Cytotoxic T lymphocyte reactivity to gp100, MelanA/MART-1, and tyrosinase, in HLA-A2-positive vitiligo patients.

Vitiligo is a common depigmentation disorder thought to result from autoimmune destruction of melanocytes. Recent studies suggest a role for cell-mediated immune responses to melanocyte differentiation antigens, including gp100, MelanA/MART-1, and tyrosinase, in vitiligo pathogenesis. This study investigated T cell reactivity to MelanA/MART-1, tyrosinase, and gp100, in HLA-A2-positive patients with vitiligo. Melanocyte-specific T cell responses were measured ex vivo via enzyme-linked immunospot assay following stimulation with MelanA/MART-1, tyrosinase, and modified gp100 epitopes. Antigen-specific T lymphocyte reactivity to gp100 peptides was seen in 15 of 17 (88%) patients, with many demonstrating very high reactivity at levels comparable with those observed with common recall antigens. Reactivity to gp100 was noted to be associated with disease activity. Antigen-specific T lymphocyte reactivity to MelanA/MART-1 and tyrosinase peptides was not observed ex vivo in our patients, and only one patient demonstrated responses to MelanA/MART-1 and tyrosinase peptides following in vitro re-stimulation. Our findings implicate T cell reactivity to gp100 in patients with active disease and support the concept of an immunopathologic mechanism in vitiligo, in which cell-mediated responses to normal melanocyte antigens play a crucial part.

Antigens, Neoplasm↗
PubMed2002

Cutting edge: impaired Toll-like receptor expression and function in aging.

Toll-like receptors (TLR) are pattern recognition receptors that recognize conserved molecular patterns on microbes and link innate and adaptive immune systems. We investigated whether the enhanced susceptibility to bacterial, yeast, and viral infections and poor adaptive immune responses in aging are a result of diminished expression and function of TLRs. We examined the expression and function of all murine TLRs on macrophages from young and aged mice. Both splenic and activated peritoneal macrophages from aged mice expressed significantly lower levels of all TLRs. Furthermore, macrophages from aged mice secreted significantly lower levels of IL-6 and TNF-alpha when stimulated with known ligands for TLR1 and 2, 2 and 6,TLR3, TLR4, TLR5, and TLR9 when compared with those from young mice. These results support the concept that increased susceptibility to infections and poor adaptive immune responses in aging may be due to the decline in TLR expression and function.

Aging↗
PubMed2002

DNA vaccine expressing conserved influenza virus proteins protective against H5N1 challenge infection in mice.

Influenza vaccination practice, which is based on neutralizing antibodies, requires being able to predict which viral strains will be circulating. If an unexpected strain, as in the 1997 H5N1 Hong Kong outbreak, or even a pandemic emerges, appropriate vaccines may take too long to prepare. Therefore, strategies based on conserved influenza antigens should be explored. We studied DNA vaccination in mice with plasmids expressing conserved nucleoprotein (NP) and matrix (M) from an H1N1 virus. After vaccination, mice were challenged with A/H5N1 viruses of low, intermediate, and high lethality. A/NP+A/M DNA vaccination reduced replication of A/Hong Kong/486/97 (HK/486), a nonlethal H5N1 strain, and protected against lethal challenge with more virulent A/Hong Kong/156/97 (HK/156). After HK/156 exposure, mice survived rechallenge with A/Hong Kong/483/97 (HK/483), although the DNA vaccination alone protected poorly against this highly virulent strain. In the absence of antigenically matched hemagglutinin-based vaccines, DNA vaccination with conserved influenza genes may provide a useful first line of defense against a rapidly spreading pandemic virus.

Animals↗