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Biomedical subjects

A Lalvani

Publications and source records attributed to A Lalvani.

At least 19 recordsLinked to original sources
PubMed2000

Influence of vitamin D deficiency and vitamin D receptor polymorphisms on tuberculosis among Gujarati Asians in west London: a case-control study.

BACKGROUND: Susceptibility to disease after infection by Mycobacterium tuberculosis is influenced by environmental and host genetic factors. Vitamin D metabolism leads to activation of macrophages and restricts the intracellular growth of M. tuberculosis. This effect may be influenced by polymorphisms at three sites in the vitamin D receptor (VDR) gene. We investigated the interaction between serum vitamin D (25-hydroxycholecalciferol) concentrations and VDR genotype on susceptibility to tuberculosis. METHODS: This study was a hospital-based case-control analysis of Asians of Gujarati origin, a mainly vegetarian immigrant population with a high rate of tuberculosis. We typed three VDR polymorphisms (defined by the presence of restriction endonuclease sites for Taq1, Bsm1, and Fok1) in 91 of 126 untreated patients with tuberculosis and 116 healthy contacts who had been sensitised to tuberculosis. Serum 25-hydroxycholecalciferol was recorded in 42 contacts and 103 patients. FINDINGS: 25-hydroxycholecalciferol deficiency was associated with active tuberculosis (odds ratio 2.9 [95% CI 1.3-6.5], p=0.008), and undetectable serum 25-hydroxycholecalciferol (<7 nmol/L) carried a higher risk of tuberculosis (9.9 [1.3-76.2], p=0.009). Although there was no significant independent association between VDR genotype and tuberculosis, the combination of genotype TT/Tt and 25-hydroxycholecalciferol deficiency was associated with disease (2.8 [1.2-6.5]) and the presence of genotype ff or undetectable serum 25-hydroxycholecalciferol was strongly associated with disease (5.1 [1.4-18.4]). INTERPRETATION: 25-hydroxycholecalciferol deficiency may contribute to the high occurrence of tuberculosis in this population. Polymorphisms in the VDR gene also contribute to susceptibility when considered in combination with 25-hydroxycholecalciferol deficiency.

Calcifediol↗
PubMed2000

High frequencies of circulating IFN-gamma-secreting CD8 cytotoxic T cells specific for a novel MHC class I-restricted Mycobacterium tuberculosis epitope in M. tuberculosis-infected subjects without disease.

MHC class I-restricted CD8 cytotoxic T lymphocytes (CTL) are essential for protective immunity to Mycobacterium tuberculosis in animal models but their role in humans remains unclear. We therefore studied subjects who had successfully contained M. tuberculosis infection in vivo, i.e. exposed healthy household contacts and individuals with inactive self-healed pulmonary tuberculosis. Using the ELISPOT assay for IFN-gamma, we screened peptides from ESAT-6, a secreted antigen that is highly specific for M. tuberculosis. We identified a novel nonamer epitope: unstimulated peripheral blood-derived CD8 T cells displayed peptide-specific IFN-gamma release ex vivo while CD8 T cell lines and clones exhibited HLA-A68.02-restricted cytolytic activity and recognized endogenously processed antigen. The frequency of CD8 CTL specific for this single M. tuberculosis epitope, 1/2500 peripheral blood lymphocytes, was equivalent to the combined frequency of all IFN-gamma-secreting purified protein derivative-reactive T cells ex vivo. This highly focused CTL response was maintained in an asymptomatic contact over 2 years and is the most potent antigen-specific antimycobacterial CD8 CTL response hitherto described. Thus, human M. tuberculosis-specific CD8 CTL are not necessarily associated with active disease per se. Rather, our results are consistent with a protective role for these ESAT-6-specific CD8 T cells in the long-term control of M. tuberculosis in vivo in humans.

Amino Acid Sequence↗
PubMed2000

Cytotoxic T-lymphocyte epitopes for HLA-B53 and other HLA types in the malaria vaccine candidate liver-stage antigen 3.

The development of an effective preerythrocytic vaccine against Plasmodium falciparum malaria is likely to require inclusion of components from several preerythrocytic antigens. The association of HLA-B53 with resistance to severe malaria in West Africa provided evidence that HLA class I-restricted CD8(+) T-cell responses play a role in protective immunity in African children, supporting data from rodent models of malaria. Previously, a single epitope from liver-stage-specific antigen 1 (LSA-1) has been shown to be recognized by HLA-B53-specific cytotoxic T lymphocytes (CTL), but HLA-B53 epitopes were not found in four other antigens. In this study we measured CTL responses to peptides from the recently sequenced antigen liver-stage antigen 3 (LSA-3) and identified in it a new epitope restricted by HLA-B53. Several CTL epitopes restricted by other class I types were also identified within LSA-3 in studies in The Gambia and Tanzania. CTL were also identified to an additional P. falciparum antigen, exported protein 1 (Exp-1), the homologue of which is a protective antigen in a rodent model of malaria. These findings emphasize the diversity of P. falciparum antigens recognized by CD8(+) T cells in humans and support the inclusion of components from several antigens in new CTL-inducing vaccines against malaria.

Amino Acid Sequence↗
PubMed1999

Potent induction of focused Th1-type cellular and humoral immune responses by RTS,S/SBAS2, a recombinant Plasmodium falciparum malaria vaccine.

The RTS,S/SBAS2 vaccine confers sterile protection against Plasmodium falciparum sporozoite challenge. The mechanisms underlying this are of great interest, yet little is known about the immune effector mechanisms induced by this vaccine. The immune responses induced by RTS,S/SBAS2 were characterized in 10 malaria-naive volunteers. Several epitopes in the circumsporozoite protein (CSP) were identified as targets of cultured interferon (IFN)-gamma-secreting CD4+ T cells. RTS,S-specific IFN-gamma-secreting effector T cells were induced in 8 subjects; this ex vivo response mapped to a single peptide in Th2R. CSP-specific CD8+ cytotoxic T lymphocytes were not detected. RTS, S-specific IFN-gamma production was universal, whereas interleukin-4 and -5 production was rare. RTS,S-specific lymphoproliferative responses and antibodies to CSP were strongly induced in all volunteers. Responses waned with time but were boostable. Thus, RTS, S/SBAS2 is a potent inducer of Th1-type cellular and humoral immunity. These results highlight possible immune mechanisms of protection and have important implications for vaccine design in general.

Adult↗
PubMed1999

Acute pulmonary schistosomiasis in travelers returning from Lake Malawi, sub-Saharan Africa.

We describe four cases of acute schistosomiasis presenting to the Infectious Diseases Unit of John Radcliffe Hospital (Oxford, England) during a 2-month period in autumn 1997. All four patients had swum in Lake Malawi, a freshwater lake in sub-Saharan Africa that is associated with Schistosoma haematobium and, less commonly, Schistosoma mansoni infections. All four patients had a severe acute illness and had prominent pulmonary involvement, both clinically and radiologically. This represents a change in the recognized pattern of presentation and could possibly reflect a new parasite variant in the lake.

Acute Disease↗
PubMed1998

Human cytolytic and interferon gamma-secreting CD8+ T lymphocytes specific for Mycobacterium tuberculosis.

Protective immunity to Mycobacterium tuberculosis is poorly understood, but mounting evidence, at least in animal models, implicates major histocompatibility complex class I-restricted CD8+ T cells as an essential component. By using a highly sensitive assay for single cell interferon gamma release, we screened an array of M. tuberculosis antigen-derived peptides congruent with HLA class I allele-specific motifs. We identified CD8+ T cells specific for epitopes in the early secretory antigenic target 6 during active tuberculosis, after clinical recovery and in healthy contacts. Unrestimulated cells exhibited peptide-specific interferon gamma secretion, whereas lines or clones recognized endogenously processed antigen and showed cytolytic activity. These results provide direct evidence for the involvement of CD8+ cytotoxic T lymphocytes in host defense against M. tuberculosis in humans and support current attempts to generate protective cytotoxic T lymphocyte responses against M. tuberculosis by vaccination.

Adult↗
PubMed1998

Cytotoxic T-lymphocytes against malaria and tuberculosis: from natural immunity to vaccine design.

1. Mycobacterium tuberculosis and the liver stage of Plasmodium falciparum are intracellular pathogens which are potentially susceptible to cytotoxic T-lymphocytes, a crucial component of the protective immune response to viral infections. Evidence from animal models points to a protective role for cytotoxic T-lymphocytes against M. tuberculosis and P. falciparum, but cytotoxic T-lymphocytes specific for these pathogens have been difficult to identify in man.2. Using a reverse immunogenetic approach, candidate epitopes from selected antigens of P. falciparum and M. tuberculosis were used to detect peptide-specific cytotoxic T-lymphocyte responses in individuals exposed to these pathogens. Cytotoxic T-lymphocyte activity was detected by the 51Cr release cytotoxicity assay and a sensitive ELISPOT assay for single-cell interferon-gamma release.3. In naturally exposed, partially immune Africans in The Gambia, eight largely conserved cytotoxic T-lymphocyte epitopes in P. falciparum, restricted by several different HLA class I alleles, were identified. Several epitopes were also recognized in Tanzanians and cytotoxic T-lymphocytes recognized endogenously processed antigen.4. In tuberculosis patients with HLA-B52, a CD8+ cytotoxic T-lymphocyte epitope was identified in ESAT-6, a secreted antigen specific for M. tuberculosis complex but absent in BCG. Cytotoxic T-lymphocytes exhibited HLA-B52-restricted peptide-specific interferon-gamma release and lytic activity and recognized endogenously processed antigen.5. These studies demonstrate that CD8+ cytotoxic T-lymphocytes specific for mycobacterial and protozoal antigens are induced during natural infections in humans. The identification of these T-cells endorses current strategies to develop cytotoxic T-lymphocyte-inducing vaccines against P. falciparum and M. tuberculosis and highlights candidate antigens for inclusion in subunit vaccines.

Animals↗
PubMed1998

38 000 MW antigen-specific major histocompatibility complex class I restricted interferon-gamma-secreting CD8+ T cells in healthy contacts of tuberculosis.

CD8+ T lymphocytes are required to protect mice against Mycobacterium tuberculosis, although in early infection the mechanism appears not to be via perforin or granzyme-mediated lysis of the infected target, and may be via interferon-gamma (IFN-gamma) production. We therefore investigated whether CD8+ T cells specific for the immunoprotective 38 000 MW antigen of M. tuberculosis could be detected in infected humans. Using a recombinant vaccinia virus expressing the 38 000 MW antigen of M. tuberculosis (rV38) and a control vaccinia virus (rVras) we demonstrated that both viruses stimulated IFN-gamma production from freshly isolated peripheral blood mononuclear cells (PBMC) in a 36-hr enzyme-linked immunospot assay. Cell depletion and antibody blockade established that the bulk of the 38 000 MW antigen-specific IFN-gamma response was mediated by CD8+, major histocompatibility complex class I-restricted T cells, whereas the anti-vaccinia virus response was predominantly mediated by CD4+ T cells. In further evaluations PBMC from all seven healthy tuberculosis-exposed contacts had a 38 000 MW antigen-specific IFN-gamma response, whereas seven patients with untreated sputum-positive pulmonary tuberculosis had very low levels of 38 000 antigen-specific IFN-gamma-producing cells. These preliminary observations demonstrate the utility of recombinant vaccinia viruses in restimulating freshly isolated CD4+ and CD8+ T cells. The bias towards a higher frequency of IFN-gamma-producing CD8+ T cells in contacts rather than patients may indicate a protective role for CD8+ cells in human tuberculosis.

Adult↗
PubMed1998

Phase I/IIa safety, immunogenicity, and efficacy trial of NYVAC-Pf7, a pox-vectored, multiantigen, multistage vaccine candidate for Plasmodium falciparum malaria.

Candidate malaria vaccines have failed to elicit consistently protective immune responses against challenge with Plasmodium falciparum. NYVAC-Pf7, a highly attenuated vaccinia virus with 7 P. falciparum genes inserted into its genome, was tested in a phase I/IIa safety, immunogenicity, and efficacy vaccine trial in human volunteers. Malaria genes inserted into the NYVAC genome encoded proteins from all stages of the parasite's life cycle. Volunteers received three immunizations of two different dosages of NYVAC-Pf7. The vaccine was safe and well tolerated but variably immunogenic. While antibody responses were generally poor, cellular immune responses were detected in >90% of the volunteers. Of the 35 volunteers challenged with the bite of 5 P. falciparum-infected Anopheles mosquitoes, 1 was completely protected, and there was a significant delay in time to parasite patency in the groups of volunteers who received either the low or high dose of vaccine compared with control volunteers.

Adolescent↗
PubMed1997

Optimization of a peptide-based protocol employing IL-7 for in vitro restimulation of human cytotoxic T lymphocyte precursors.

A variety of different methods for the in vitro restimulation of human cytotoxic T lymphocyte (CTL) precursors (CTLp) are in use. Our aim was to enhance the detection of circulating human CTLp in peripheral blood. We have developed a standardized and highly efficient method for restimulating CTLp. Synthetic peptides were used to restimulate cognate CTLp from peripheral blood mononuclear cells (PBMC), and effector CTL capable of lysing peptide-pulsed and virus infected targets were generated. The effects of several parameters on CTL specific for influenza A, EBV and HIV-1 were evaluated, and the optimum peptide concentration for CTL generation was established. Supplementation of initial cultures with IL-7 greatly enhanced peptide-specific lytic activity for all peptides tested and the dose-response relationship for IL-7 was delineated. A novel technique using peptide-MHC class I molecule tetramers to stain T cells bearing cognate T cell receptors permitted enumeration of antigen-specific CD8 + CTL during in vitro restimulation; IL-7 supplementation selectively expanded the population of peptide-specific CD8 + CTL. Importantly, this protocol, whilst enhancing the restimulation and lytic activity of secondary CTL, does not induce primary CTL in vitro. The improved efficiency with which CTL are generated in this system substantially enhances the sensitivity of CTL culture and the 51Cr release assay to detect low levels of CTL activity.

Antigen Presentation↗
PubMed1997

Rapid effector function in CD8+ memory T cells.

The nature of the CD8+ T cells that underlie antiviral protective immunological memory in vivo is unclear. We have characterized peptide-specific CD8+ T lymphocytes directly ex vivo from peripheral blood in humans with past exposure to influenza virus, using single cell interferon gamma (IFN-gamma) release as a measure of effector function. In individuals in the memory state with respect to influenza virus infection, unrestimulated antigen-specific CD8+ T cells displayed IFN-gamma release within 6 h of antigen contact, identifying a population of memory CD8+ T cells that exhibit effector function without needing to divide and differentiate over several days. We have quantified circulating CD8+ effector T cells specific for six different MHC class I-restricted influenza virus epitopes. Enumeration of these CD8+ T cells gives frequencies of peptide-specific T cells that correlate with, but are in general severalfold higher than, CTL precursor frequencies derived from limiting dilution analysis, indicating that this novel population of memory CD8+ T cells has hitherto been undetected by standard means. The phenotype of these cells, which persist at a low frequency long after recovery from an acute viral infection, suggests that they play a role in protective immunological memory.

Adult↗
PubMed1997

Recombinant vaccinia viruses for the characterization of Plasmodium falciparum-specific cytotoxic T lymphocytes: recognition of processed antigen despite limited re-stimulation efficacy.

Cytotoxic T lymphocytes (CTL) have been implicated in immunity to Plasmodium falciparum infection and disease. We have previously described the use of peptides to define malaria-specific CTL epitopes. To determine whether these peptide epitopes are processed intracellularly from the whole antigen we have developed recombinant vaccinia viruses (rVV) expressing three malaria antigens: thrombospondin-related adhesive protein (TRAP), Pfs16 and the C-terminal half of liver-stage antigen (LSA)-1. Target cells infected with recombinant viruses were lysed by malaria-specific CTL from semi-immune African donors. We also tested the ability of cells infected with these recombinant vaccinia viruses to re-stimulate malaria-specific CTL in peripheral blood lymphocytes from malaria immune adults. Two other pox virus recombinants, NYVAC, an attenuated vaccinia virus, and ALVAC, a canarypox virus, both expressing malaria antigens were also evaluated for their ability to stimulate malaria-specific CTL in contrast to peptide, none of these viruses successfully re-stimulated CTL from the peripheral blood lymphocytes of semi-immune donors. The ability of human CTL from naturally exposed individuals to recognize processed antigen supports the relevance of these cells in protective immunity to malaria.

Adult↗
PubMed1997

Sensitivity to bee and wasp venoms: association with specific IgE responses to the bee and wasp venom and HLA DRB1 and DPB1.

BACKGROUND: Stings from bees and wasps can cause systemic reactions which can be fatal in some individuals. In these venom-sensitive patients, specific IgE to the venom is produced and is considered to participate in the adverse reactions. This immune response requires antigen presentation by human leucocyte antigens (HLA) class II molecules, which includes DR and DP, which are present on antigen presenting cells. OBJECTIVE: To test for associations between HLA class II DRB1 and DPB1 alleles and life-threatening sensitivity to both bee and wasp venoms. To establish further whether any associations are independent of the atopy phenotype. METHODS: A total of 33 bee- and 44 wasp-venom-sensitive patients was studied. DRB1 genotypes were determined by single stranded oligonucleotide (SSO) probing of PCR products, and DPB1 genotypes by amplified fragment length polymorphism (AFLP) analysis. Total and specific IgE were measured using the Pharmacia Immunocap, FEIA. Patients with specific IgE to the venom antigens only were termed monosensitive and those with additional specific IgE to HDM and/or GP were termed polysensitive. RESULTS: Allele frequencies were compared to an unrelated control population. The 33 bee-sensitive patients had a greater prevalence of DRB1*07 alleles than the control subjects, 26% vs 14%, with an odds ratio (OR) of 2.1 (95% CI, 1.2-3.7, P = 0.015, corrected for multiple comparisons, Pc = ns). This association was confined to the 15 monosensitive bee patients, who had a 43% DRB1*07 allele frequency when compared with 11% in the 18 polysensitive bee patients, OR 6.1 (95% CI, 1.73-22, P = 0.004, Pc = 0.05), and when compared with a control group of non-venom subjects, 43% vs 16%, OR 3.9 (95% CI, 1.72-9.0, P = 0.002, Pc = 0.02). The 44 wasp-sensitive patients had an increase in the DRB1*11 allele when compared with the control subjects, 13% vs 6%, with an OR 2.2 (95% CI, 1.0-4.6, P = 0.04, Pc = NS), and a decreased prevalence of DRB1*04 alleles, 10% vs 19%, with an OR 0.33 (95% CI, 0.24-0.99, P = 0.04, Pc = NS), but these were not significant when multiple comparisons were taken into account. The DPB1 alleles were not significantly different between the venom sensitive patients and the controls. CONCLUSION: Patients monosensitive to bee venom had a significantly greater prevalence of DRB1*07 alleles than the non-venom, control population suggesting that IgE responses in these patients may, in part be controlled by immune response HLA class II genes. These results are also suggestive of wasp-sensitive patients having a higher prevalence of DRB1*11 and a lower prevalence of DRB1*04 than the control population.

Adolescent↗
PubMed1996

Cytotoxic T lymphocytes to Plasmodium falciparum epitopes in an area of intense and perennial transmission in Tanzania.

Studies in The Gambia have provided indirect evidence that cytotoxic T lymphocytes (CTL) play a protective role against malaria in humans and recently, using allele-specific HLA class I peptide motifs, several peptide epitopes for CTL in four pre-erythrocytic Plasmodium falciparum antigens have been identified in naturally exposed Gambians. However, CTL levels were low, suggesting that boosting these low levels by immunization might provide substantial protection. In the Kilombero valley of Tanzania, malaria transmission is holoendemic and 300 times more intense than in The Gambia. We report here that several of the epitopes identified in The Gambia are also recognized in naturally exposed, partially immune Tanzanian adults and that levels of CTL are similar to or slightly higher than in Gambian subjects, despite the much higher inoculation rate. We report a new HLA-A2.1-restricted epitope from the thrombospondin-related anonymous protein (TRAP) and we demonstrate that peptide epitopes in TRAP are naturally processed for recognition by CTL from naturally exposed humans. The common allele of a variable HLA-B7-restricted epitope in the circumsporozoite protein behaved as an altered peptide ligand (APL) with respect to CTL cognate for a rarer allelic variant of this epitope, suggesting that APL antagonism may occur in natural CTL responses to P. falciparum. The moderate levels of CTL observed, even in this area of intense malaria transmission, points to the need to assess candidate vaccines aimed at increasing CTL levels.

Adult↗
PubMed1996

Psittacosis associated with bilateral 4th cranial nerve palsies.

We report a 55-year-old man who presented with a moderately severe community acquired pneumonia due to Chlamydia psittaci, probably acquired from budgerigars. One of his presenting symptoms was diplopia, secondary to bilateral 4th cranial nerve palsies, which persisted for some months. The literature on neurological complications of pneumonia is reviewed.

Chlamydophila psittaci↗
PubMed1995

Identification of conserved antigenic components for a cytotoxic T lymphocyte-inducing vaccine against malaria.

Several cellular and humoral mechanisms probably play a role in natural immunity to Plasmodium falciparum malaria, but the development of an effective vaccine has been impeded by uncertainty as to which antigens are targeted by protective immune responses. Experimental models of malaria have shown that cytotoxic T lymphocytes (CTL) which kill parasite-infected hepatocytes can provide complete protective immunity against certain species of Plasmodium in mice, and studies in The Gambia have provided indirect evidence that CTL play a protective role against P falciparum in humans. By using an HLA-based approach, termed reverse immunogenetics, we have previously identified peptide epitopes for CTL in liver-stage antigen-1 and the circumsporozoite protein of P falciparum. We have extended this work to identify CTL epitopes for HLA class I antigens that are found in most individuals from Caucasian and African populations. Most of these epitopes are in conserved regions of P falciparum. CTL peptide epitopes were found in a further two antigens, thrombospondin-related anonymous protein and sporozoite threonine and asparagine rich protein, indicating that a subunit vaccine designed to induce a protective CTL response may need to include parts of several parasite antigens. However, CTL levels in both children with malaria and in semi-immune adults from an endemic area were low suggesting that boosting these low levels by immunisation might provide substantial or even complete protection against infection and disease.

Adult↗
PubMed1994

Human leukocyte antigens and natural selection by malaria.

The extraordinary polymorphism of human leukocyte antigens (HLA) poses a question as to how this remarkable diversity arose and is maintained. The explanation that infectious pathogens are largely responsible is theoretically attractive but clear and consistent associations between HLA alleles and major infectious diseases have rarely been identified. Large case-control studies of HLA types in African children with severe malaria indicate that HLA associations with this parasitic infection do exist and it is becoming possible to investigate the underlying mechanisms by identification of peptide epitopes in parasite antigens. Such analysis reveals how the magnitude and detectability of HLA associations may be influenced by numerous genetic and environmental factors. These complex interactions will give rise to variation over time and space in the selective pressures exerted by infectious diseases and this fluctuation may, in itself, contribute to the maintenance of HLA polymorphism.

Biological Evolution↗