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Biomedical subjects

S Hawke

Publications and source records attributed to S Hawke.

At least 19 recordsLinked to original sources
PubMed2006

Antibody-mediated neuronal apoptosis: therapeutic implications for prion diseases.

Neuronal cell death is considered to be a hallmark in prion diseases. These disorders are believed to result from the post-translational conversion of a normal cell membrane sialoglycoprotein PrPC, composed primarily of alpha-helical structure, into a disease specific isoform, PrPSc that is rich in beta-sheet and partially proteinase-resistant. Recent in vivo studies indicate that prion replication can be inhibited by anti-PrP monoclonal antibodies that led to the indefinite delay in the development of prion disease. The recent report by Solforosi and colleagues has increased the need to understand pathway(s) leading to prion-associated apoptosis and neuronal death thought to be the cause of death in transmissible spongiform encephalopathy (TSE) individuals. Furthermore, these reports increased momentum about the use of antibody-based therapy in prion diseases, although great caution should be exerted when using anti-prion antibodies directly into the central nervous system (CNS) with special emphasis on refined strategies such as specific targeting of regions of the prion protein thought not to be involved in signalling pathways.

Animals↗
PubMed2004

Distribution and quantification of human herpesvirus 6 in multiple sclerosis and control brains.

Multiple sclerosis (MS) is thought to be precipitated by environmental factors, potentially including viruses, in genetically susceptible individuals and recently human herpesvirus 6 (HHV-6) has been associated with the disease. We have analysed post mortem brain for the presence, variant type and quantity of HHV-6 by PCR. A total of 124 samples from seven anatomically defined regions of brain were tested from MS cases and controls. HHV-6 DNA was detected in 41% and 44% of MS case and control samples. The median viral loads were 11 and 9 genome copies/microg DNA in cases and controls respectively and the viral load was not increased in lesions. Except in one instance, the HHV-6 DNA detected was variant B. There was no apparent difference in the distribution of HHV-6 DNA in the brains of MS cases versus controls, nor between normal appearing and lesional tissue in MS cases. Periventricular regions of the brain were more frequently positive for HHV-6 DNA in both MS cases and controls, although this difference was not statistically significant. These studies confirm the neurotropism of HHV-6 but do not demonstrate differences in the distribution, variant type or quantity of HHV-6 in brains from patients with MS versus controls.

Aged↗
PubMed2002

Uncoupling of virus-induced inflammation and anti-viral immunity in the brain parenchyma.

Non-neuroadapted influenza virus confined to the brain parenchyma does not induce antigen-specific immunity. Nevertheless, infection in this site upregulated major histocompatibility complex (MHC) class I and MHC class II expression and recruited lymphocytes to a perivascular compartment. T cells recovered from the brain had an activated/memory phenotype but did not respond to viral antigens. In contrast, T cells recovered from the brain after infection in a lateral cerebral ventricle, which is immunogenic, showed virus-specific responses. As with infectious virus, influenza virus-infected dendritic cells elicited virus-specific immunity when inoculated into the cerebrospinal fluid but not when inoculated into the brain parenchyma. Thus, inflammation and dendritic cell function were both uncoupled from immune priming in the microenvironment of the brain parenchyma and neither was sufficient to overcome immunological privilege.

Animals↗
PubMed1999

Cross-restriction of a T cell clone to HLA-DR alleles associated with rheumatoid arthritis: clues to arthritogenic peptide motifs.

OBJECTIVE: To identify distinctive sequence motifs required for productive peptide presentation by those HLA-DR alleles/DR4 subtypes that predispose to rheumatoid arthritis (RA). METHODS: We tested 10 different HLA-DR4 subtypes for presentation of acetylcholine receptor peptides to 8 different DR4-restricted T cell lines/clones in proliferation assays. RESULTS: Seven of the 8 T cells depended absolutely on either the autologous Lys71 (in Dw4) or Arg71 (e.g., Dw14), despite these alleles' similar charge and RA associations. In contrast, the PM-A T cell was only mildly affected by this interchange. Moreover, after minor modifications, peptides were presented to this unusual T cell preferentially by all the RA-associated subtypes of DR4 as well as by 2 other DR alleles (DR1 and DR1402) that predispose to RA. CONCLUSION: This coincident cross-restriction to all the RA-associated HLA-DR alleles except DR10 shows that there could even be a single arthritogenic peptide; we now suggest a possible consensus motif.

Alleles↗
PubMed1999

Distant interactions between dimorphisms in HLA-DR4 radically affect recognition of defined peptides by a specific T cell clone.

Several isolated dimorphisms recur in many HLA class II alleles, but it is not clear whether they merely influence the binding of peptides locally or have more general effects on their recognition by T cells. For example, interchanges in HLA-DRbeta include 86Gly <--> Val and 57Asp <--> Ser at either end of its alpha helix, and 71Arg <--> Lys in the middle. In DR4, the existence of six subtypes differing by single substitutions at these sites enabled us to assess their functional effects--both in isolation and in their natural context--on peptide presentation to a specific T cell clone with unusually broad cross-restrictions. Unexpectedly, the restriction imposed by 86Val was much more severe in the context of 71Arg than 71Lys, but was also more readily overcome by reducing the bulk of the 'p1' peptide 'anchor' residue (149Trp --> Phe). Moreover, when there was also a distant 57Asp-->Ser substitution, compensating similarly for 86Val proved much more difficult. Thus 86Val and 57Ser in combination had far more drastic effects on peptide presentation than they did separately, when peptide binding was also largely unchanged. These and other interactions with position 71 together provide strong evidence that the configuration of the peptide-DR4 complex is critical for T cell recognition, which could be affected by subtle conformational influences on the p1-9 core of the peptide or on the alpha helix of DR4beta (between positions 86 and 57). Ideally, therefore, the effects of individual class II substitutions should be considered in their natural context rather than in isolation.

Alleles↗
PubMed1998

Long-term persistence of activated cytotoxic T lymphocytes after viral infection of the central nervous system.

Mice intranasally inoculated with influenza A/X-31 are protected against a subsequent intracerebral challenge with the neurovirulent influenza A/WSN and this heterotypic protection is mediated by CD8(+) cytotoxic T lymphocytes. We have studied the kinetics of this secondary immune response and found that despite the elimination of replication-competent virus by day 10, we were able to recover activated influenza-specific cytotoxic T lymphocytes (CTLs) that killed freshly ex vivo from the brains of mice for at least 320 d after the intracerebral inoculation. The activated antiviral CTLs expressed high levels of the early activation marker CD69, suggesting continuing TCR signaling despite a lack of viral protein and major histocompatibility complex staining by immunohistochemistry in the brain parenchyma and barely detectable levels of viral nucleic acid by single and two-step reverse transcription PCR. Local persistence of activated lymphocytes may be important for efficient long-term responses to viruses prone to recrudesce in sites of relative immune privilege.

Animals↗
PubMed1997

Virus dissemination through the brain parenchyma without immunologic control.

After inoculation into the cerebrospinal fluid, the neurovirulent influenza virus A/WSN caused a rapidly progressive encephalitis that was uniformly fatal within 8 days. After inoculation into the brain parenchyma, the same virus replicated for 7 to 20 days without causing clinical illness, but when infection reached the cerebrospinal fluid, encephalitis was lethal within a further 6 days. As the virus spread through the brain parenchyma, there was intense intracerebral inflammation, with up-regulation of MHC class I and MHC class II expression and recruitment of CD44(high) CD49d(high) T cells. However, this was not associated with antiviral Ab production, and the infiltrating cells, unlike primed A/WSN-specific T cells, did not eliminate the virus in vivo or show evidence of virus recognition in vitro. Thus, a neurovirulent virus was able to disseminate widely through the brain parenchyma and induce considerable intracerebral inflammation without eliciting protective immunity.

Animals↗
PubMed1997

Protection against influenza virus encephalitis by adoptive lymphocyte transfer.

CD8+ cytotoxic T lymphocytes (CTL) have an established role in anti-viral immunity, but whether CTL function efficiently in the brain remains unclear. In particular, virus-infected neurons, which express only low levels of MHC class I antigens and are resistant to the induction of apoptosis, could constitute a relatively intractable CTL target. We have used immune lymphocytes adoptively transferred into the CSF to protect naive mice against an intracerebral infection with influenza A/WSN, a virus that infects neurons in the brain parenchyma and causes a lethal encephalitis. After in vitro restimulation, heterotypically immune spleen cells protected against A/WSN encephalitis in an H-2-restricted, CD8-dependent, CD4-independent manner. Adoptively transferred CTL clones were also protective. Homotypically immune spleen cells additionally mediated CD8-independent, H-2-unrestricted protection, probably due to the generation of A/WSN-specific plasma cells from memory B cells during in vitro restimulation. Thus after in vitro restimulation, either CTL or B cells adoptively transferred into the CSF protected against an acutely lethal intracerebral virus infection.

Animals↗
PubMed1997

Recruitment, activation and proliferation of CD8+ memory T cells in an immunoprivileged site.

The capacity of a memory cytotoxic T lymphocyte (CTL) population to protect against viral infections is well established, but the processes underlying this protection are less well understood. We have used heterotypic intranasal immunization with influenza A/X31 (H3N2) to protect against a subsequent infection with the neurovirulent influenza A/WSN (H1N1) in either the cerebrospinal fluid or the immunoprivileged brain parenchyma. Viral clearance from both sites was associated with a local infiltration and proliferation of A/WSN-specific CD8+ T cells. Infection in the cerebrospinal fluid elicited a proliferative response in the draining lymph nodes, an anti-H1N1 serum antibody response and an increase in the extracerebral A/WSN-specific CTL precursor frequency. In contrast, infection in the brain parenchyma elicited no lymph node proliferative response or serum antibody response and caused a transient decrease in the extracerebral CTL precursor frequency. Thus the memory CTL population protected against an intracerebral viral infection independent of any immune response occurring in systemic lymphoid tissue.

Animals↗
PubMed1997

The immunogenicity of intracerebral virus infection depends on anatomical site.

The brain parenchyma affords immune privilege to tissue grafts, but it is not known whether the same is true for intracerebral viral infections. Using stereotactically guided microinjection, we have confined infection with influenza virus A/NT/60/68 to either the brain parenchyma or the cerebrospinal fluid (CSF). A/NT/60/68 infection in the CSF elicited a comparable immune response to intranasal infection, with the production of antiviral serum antibody, priming of antiviral cytotoxic T-cell precursors, and an antiviral proliferative response in the draining lymph nodes. The response to virus in the CSF was detectable sooner after inoculation than the response to intranasal virus and also involved a prolonged production of virus-specific immunoglobulin A in the CSF. In contrast, there was no detectable immune response to virus infection in the brain parenchyma by any of the parameters measured for at least 10 days after inoculation. Over the next 80 days, 46% of the mice given parenchymal virus developed low-level immune responses that did not involve CSF antibody production, while the remaining 54% had no detectable response at any time. Thus, a virus infection confined to the parenchymal substance of the brain primed the immune system inefficiently or not at all.

Animals↗
PubMed1996

Association of arthrogryposis multiplex congenita with maternal antibodies inhibiting fetal acetylcholine receptor function.

Arthrogryposis multiplex congenita (AMC), characterized by multiple joint contractures developing in utero, results from lack of fetal movement. Some cases are genetically determined, but AMC occasionally complicates pregnancy in patients with myasthenia gravis (MG) suggesting involvement of circulating maternal antibodies. We previously demonstrated antibodies that inhibited the function of fetal acetylcholine receptor (AChR) in one healthy woman with an obstetric history of recurrent AMC. Here we study sera from this woman, from one other with a similar history, and from three (one asymptomatic) whose babies had neonatal MG and AMC. All five maternal sera had high titers of antibodies that inhibited alpha-Bungarotoxin (alpha-BuTx) binding to fetal AChR, and their sera markedly inhibited fetal AChR function with little effect on adult AChR function. Moreover, in a further survey, 3 of 20 sera from anti-AChR negative AMC mothers inhibited fetal AChR function significantly at 1:100 dilution. These results demonstrate the role of antibodies to fetal AChR and perhaps other muscle antigens in some cases of AMC. More generally, they suggest that placental transfer of antibodies directed at fetal antigens should be considered as a cause of other recurrent fetal or perinatal disorders.

Adult↗
PubMed1996

Protection against lethal influenza virus encephalitis by intranasally primed CD8+ memory T cells.

The neurotropic influenza virus strain A/WSN (H1N1) caused a rapidly fatal encephalitis after intracerebral inoculation into naive mice. Intranasal immunization with the same virus (homotypic) completely protected mice against a subsequent intracerebral challenge with A/WSN; there was no clinical disease, and infectious virus could not be recovered from the brain. In vivo depletion of CD4+ or CD8+ T cell subsets did not affect homotypic protection, and the pups of immune mothers were also protected against a lethal intracerebral challenge with A/WSN, suggesting that the Ab produced by intranasal priming was sufficient to protect mice against later intracerebral infection. Intranasal immunization with the heterotypic influenza strain A/X31 (H3N2) did not generate protective Ab, but despite an acute illness, 80% of mice survived the subsequent intracerebral challenge. Immune protection was associated with CD8+ T cell infiltration throughout the brain substance, together with widespread up-regulation of intracerebral MHC class I and MHC class II expression. In vivo T cell subset depletion showed that heterotypic protection was dependent upon CD8+, but not CD4+, T cells. This model system demonstrates some of the mechanisms through which the immunity generated by an initial extracerebral virus infection may protect against later intracerebral virus replication.

Acute Disease↗
PubMed1995

Peptide-selected T cell lines from myasthenia gravis patients and controls recognize epitopes that are not processed from whole acetylcholine receptor.

To study pathogenic T helper cells in myasthenia gravis (MG) reacting against the acetylcholine receptor (AChR), we have previously selected five CD4+ T cell lines/clones from MG patients (or healthy controls) against full-length recombinant human AChR alpha subunit (alpha 1-437); these can all recognize AChR solubilized from human muscle. Recently, T cells selected with pooled AChR subunit synthetic peptides have shown greater heterogeneity than above. Hoping to validate that, we have characterized three MG and six control T cell lines selected with pooled peptides (averaging 33 residues long) covering the alpha subunit sequence; recurring responses to three particular peptides each showed preferred HLA class II restrictions--p75-115/DR4, p138-167/DR4, and p309-344/DR3 (or DR52a). However, none of three lines from MG patients recognized p138-167--even one from a previous responder to this epitope in full-length alpha 1-437; otherwise they resembled those from controls. Moreover, no peptide-selected line responded significantly to whole AChR, alpha 1-437, or even to shorter polypeptides sharing one terminus with the peptide, suggesting specificity for epitopes not naturally processed by APCs from blood. Of 20 sublines maintained with individual peptides, at least 10 responded to independently synthesized overlapping sequences, but four others depended on contaminants in the original peptides. A single line did recognize one longer polypeptide, but only after tryptic digestion; the processing of this cryptic epitope was evidently the limiting factor here rather than its concentration or the T cell sensitivity. Therefore, while synthetic peptides are essential for mapping epitopes, assessment of the pathogenic MG T cell repertoire requires full-length Ag processed naturally.

Amino Acid Sequence↗
PubMed1995

Differences in processing of an autoantigen by DR4:Dw4.2 and DR4:Dw14.2 antigen-presenting cells.

Variations in antigen processing can influence class II-restricted T cell responses. We now report a highly significant difference (p < 0.001) between the ability of antigen-presenting cells from three HLA-DR4:Dw14.2 (Arg71) and six DR4:Dw4.2 (Lys71) individuals to present recombinant or native acetylcholine receptor antigens to a myasthenia gravis T cell clone. The difference was greatest with longer antigens, and not seen with short synthetic peptides, suggesting that it may result from a difference in antigen processing between the two alleles. The results were not related to the presence of myasthenia gravis or of steroid therapy. They could, however, be of relevance in rheumatoid arthritis where particularly severe disease associates with Dw4.2/Dw14.2 heterozygosity.

Antigen-Presenting Cells↗