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L A Mitchell

Publications and source records attributed to L A Mitchell.

At least 37 records · Page 2Linked to original sources
PubMed1998

Promiscuous T-cell recognition of a rubella capsid protein epitope restricted by DRB1*0403 and DRB1*0901 molecules sharing an HLA DR supertype.

Two T cell clones derived from different donors with HLA-DRB1*0403 or DRB1*0901 phenotype recognize a rubella capsid peptide, C(265-273) in the context of several different HLA-DR molecules in addition to DRB1*0403 and DRB1*0901. All DR molecules restricting the T-cell clones have in common residues, R or Q at position beta 70, R at position beta 71, and E at position beta 74 in pocket '4' of the DR peptide binding groove, suggesting that a DR subregion structure or supertype, "Q/RRE" underlies the promiscuous T-cell recognition of this peptide. Single amino acid substituted analogs of peptide C(263-275) at anchor position 4 for natural residue R were tested for their ability to induce clonal T-cell cytotoxic responses. The results indicated that a positively charged residue, R or K, was required for T-cell recognition, suggesting a possible mechanism of electrostatic interactions between the negatively charged residue E at position beta 74 of these DR molecules and the positively charged residue at anchor position 4 of the peptide in T-cell recognition.

Amino Acid Sequence↗
PubMed1998

A new categorization of HLA DR alleles on a functional basis.

In this analysis, we introduce a new categorization of HLA DR alleles which are important members of HLA class II genes encoding cell surface glycoproteins that function to present antigenic peptides to T cells. We have grouped all HLA DR molecules into seven different functional categories on the basis of their ability to bind and present antigenic peptides to T cells and their association with susceptibility or resistance to disease. This novel categorization of DR alleles on the basis of function allows for the prediction of seven similar subregion structures (supertypes or supermotifs) within pocket 4 of HLA DR peptide binding groove as the molecular basis for grouping these alleles. The physicochemical characteristics of HLA DR supertype residues, charge in particular, may influence the selectivity for binding peptide, dominate promiscuous T-cell recognition of antigenic peptides, and affect HLA DR disease associations. To rationalize the functional categories of DR alleles, we have further combined the seven DR supertype patterns into three groups based on the charges of residues within the supertypes. Grouping HLA DR alleles into functional categories may assist in understanding the mechanistic basis of autoimmunity, resolving current paradoxes in HLA disease associations, and developing new immunotherapy strategies.

Alleles↗
PubMed1998

HLA-DR class II associations with rubella vaccine-induced joint manifestations.

HLA class II (HLA-DR) frequencies were examined in relation to incidence of acute arthralgia or arthritis in 283 white women who had received RA27/3 rubella vaccine (n = 146) or placebo (n = 137) postpartum. Leukocyte DNA was molecularly typed for HLA-DRB1 gene expression. Univariate analysis revealed higher frequencies of DR2 (odds ratio [OR], 4.8; 95% confidence interval [CI], 1.2-18.8) and DR5 (OR, 7.5; 95% CI, 1.5-37.5) but lower frequencies of DR4 (OR, 2.3; 95% CI, 1.1-4.9) and DR6 (OR, 2.8; 95% CI, 1.4-5.8), in rubella vaccinees compared with placebo recipients with arthropathy. Logistic regression modelling of DR, treatment, age, time postpartum, and arthropathy revealed that the odds of developing arthropathy was 1.9 times greater (95% CI, 1.07-3.44) after rubella vaccine than placebo. Risk for arthropathy (regardless of rubella vaccination) was also influenced by DR interactions: odds were 8 times greater in individuals with both DR1 and DR4 (95% CI, 1.45-44.02) and 7.1 times greater with both DR4 and DR6 present (95% CI, 1.85-27.52), suggesting that coexpression of these specificities may predispose to postpartum arthropathy.

Adolescent↗
PubMed1998

Point mutation of a rubella virus E1 protein T-cell epitope by substitution of single amino acid reversed the restrictive HLA-DR polymorphism: a possible mechanism maintaining HLA polymorphism.

The influence of single amino acid substitutions within a rubella E1 protein T-cell epitope, E1(273-284) on T-cell recognition was studied. Substitutions of an uncharged amino acid A for an E or for a T and substitution of a T for S were found to not significantly reduce the T-cell responses. However, substitution of a charged residue such as E for hydrophobic residues (I, V, or W); D for Q; or a relatively larger size amino acid for polar residues completely abolished the cytotoxicities mediated by E1(273-284)-specific T-cell clone. A set of single amino acid-substituted peptide analogs of E1(273-284) not eliciting cytotoxicity of the T-cell clone was used to test the influence of point mutation of the epitope on HLA DR restrictions. A panel of B-cell lines with different DR4 subtypes was used as targets in cytotoxicity assays to determine the restrictive HLA molecules. Results showed that modification of the T-cell epitope by point mutation could reverse the HLA DR restriction from one allele to other alleles. A model based on these results has been proposed to explain the mechanism balancing major histocompatibility complex (MHC) polymorphism in outbred populations.

Amino Acid Substitution↗
PubMed1997

Characterization of an overlapping CD8+ and CD4+ T-cell epitope on rubella capsid protein.

A synthetic peptide corresponding to rubella virus capsid protein residues 263 to 275 which contains an epitope recognized by a cloned CD4+ cytotoxic T-lymphocyte (CTL) line was used to induce CD8+ T-cell lines specific to this peptide. A peptide-specific CD8+ CTL clone was derived and characterized. This peptide-specific CD8+ CTL clone exhibited cytotoxicity against target cells infected by a vaccinia recombinant virus expressing rubella virus capsid protein, but not by target cells infected by vaccinia recombinant virus expressing rubella virus E1 or E2 envelope proteins. Analysis of HLA class I restriction of the CD8+ CTL clone revealed that A11 and A3 were restrictive elements. Fine mapping with truncated and overlapping peptide analogs revealed a nonamer sequence, C(264-272), as the T-cell epitope eliciting stronger cytotoxicity. Two anchor residues for binding to HLA A11 and A3 were identified at position 2 (isoleucine) and at position 9 (histidine) or at position 8 (arginine) of the epitope sequence. The identification of overlapping CD4+ and CD8+ T-cell epitopes within the capsid protein sequence C(263-275) implicates a strategy for using such epitopes in a candidate peptide-based rubella vaccine.

Amino Acid Sequence↗
PubMed1997

Randomised double-blind placebo-controlled study on adverse effects of rubella immunisation in seronegative women.

BACKGROUND: The objective of our study was to investigate the association of adverse clinical musculoskeletal and neurological events in healthy postpartum women with live attenuated (RA27/3 strain) rubella-virus vaccine, and to assess the frequency of acute and recurrent arthralgia and arthritis and associations with acute and recurrent muscle pain (myalgia) and neurological manifestations (paraesthesias). METHODS: We used a randomised placebo-controlled, double-blind design in a community setting. 636 women were enrolled and, after 90 women dropped out, 546 healthy women aged 18-41 years, who were rubella seronegative on routine screening were immunised parenterally with either monovalent live attenuated (RA27/3 strain) rubella vaccine (n = 270) or saline placebo (n = 276) in the postpartum period. Outcome measures were the occurrence of acute and persistent or recurrent joint manifestations (arthralgia or arthritis) at 1, 3, 6, 9, and 12 months after immunisation. Occurrence of muscle pain (myalgia), and neurological symptoms (paraesthesia) was also assessed at the same times. FINDINGS: 543 women completed 1-month follow-up. 456 women completed the 12-month assessment. There were no differences at the time of immunisation between rubella vaccine and placebo groups in distribution of age, ethnic origin, parity, time between delivery and immunisation, breastfeeding history, or histories of earlier rubella vaccination or joint complaints. Results indicated a significantly higher incidence (p = 0.006; odds ratio = 1.73 [95% CI = 1.17-2.57]) of acute joint manifestations in rubella-vaccine recipients (30%) than in placebo recipients (20%). Frequency of chronic (recurrent) arthralgia or arthritis was only marginally significant (p = 0.042; 1.58 [1.01-2.45]). INTERPRETATION: RA27/3 rubella vaccine given to seronegative women during the postpartum period was significantly associated with development of acute arthralgia or arthritis. Although the numbers of women assessed and length of follow-up revealed only marginally significant differences in persistent or recurrent joint manifestations between rubella vaccine and placebo recipients, it is possible that susceptible women who are given rubella vaccination may experience this outcome.

Adolescent↗
PubMed1997

New, ultrasensitive enzyme immunoassay for detecting vaccine- and disease-induced hepatitis A virus-specific immunoglobulin G in saliva.

Although detection of disease-induced hepatitis A virus (HAV)-specific antibodies in saliva has been successfully utilized in a few epidemiological studies, available assays fail to detect lower salivary anti-HAV levels associated with vaccine-induced immunity. We present a new capture enzyme immunoassay which employs a three-layer antibody recognition system. Evaluation of paired saliva-serum specimens from 1,025 international travellers, 134 other volunteers, and 91 hepatitis A vaccine recipients demonstrated 99.6% (95% confidence interval, 98.4 to 99.9) specificity and 98.7% (95% confidence interval, 97.7 to 99.4) sensitivity of this salivary assay in differentiating between immune and susceptible individuals, compared with serum-based methods. We conclude that this assay is sufficiently sensitive for reliable detection of both vaccine- and infection-induced HAV-specific immunoglobulin G in saliva, even when corresponding anti-HAV levels in serum are very low (< 1 IU/ml).

Antibodies, Viral↗
PubMed1997

HLA-DR restrictive supertypes dominate promiscuous T cell recognition: association of multiple HLA-DR molecules with susceptibility to autoimmune diseases.

The association of individual autoimmune diseases with multiple HLA molecules has remained an enigma. That T cells can recognize the same peptide presented by several different HLA-DR alleles (i.e., promiscuous recognition) has been well documented. To explain this, we propose the "DR restrictive supertype pattern (DR RSP)" hypothesis. We focus on the known amino acid polymorphisms at positions beta 70, beta 71, and beta 74 located within pocket 4 of the DR molecule and their potential influence on promiscuous T cell recognition. We have shown that HLA-DR alleles may be grouped, on the basis of their polymorphisms at these positions, into at least 6 sets of DR alleles, 4 of which share, respectively, one of the RSP: A (Q/RR/KA), D (DE/R[K]A/L), E (Q/RRE), or R (QKR/Q) and 2 of which share the restrictive patterns Q (DRQ) or a (QAA). Most of the RSP have been shown to be associated with promiscuous T cell recognition of antigenic peptides. We also provide a rationale on how different DR alleles, exhibiting a particular RSP, might be capable of binding an antigenic peptide and presenting it, in a promiscuous fashion, to peptide-specific T cells. By identifying these RSP represented by DR alleles that have been clinically associated with certain autoimmune disease, we also extend the DR RSP hypothesis to account for the association of certain autoimmune diseases with multiple HLA-DR alleles.

Arthritis, Rheumatoid↗
PubMed1996

Recognition of altered self major histocompatibility complex molecules modulated by specific peptide interactions.

Antigen-specific and major histocompatibility complex (MHC)-restricted recognition by the T cell receptor involves multiple structural contacts over a large molecular surface area. Using a human T cell clone specific for a rubella viral peptide restricted by subsets of HLA DR4 molecules, we identified structurally diverse combinations of peptide-MHC complexes which were functionally equivalent to T cell recognition. Presentation of the rubella-derived peptide on DR4 molecules with an E-74 polymorphism triggered T cell recognition, as did presentation of a single amino acid-substituted peptide in the context of DR4 molecule which lacked the E-74 site. Peptide binding and molecular modeling analysis indicates the structural and functional complementarity of T cell recognition for a specific amino acid side chain, whether contributed by the peptide or by the MHC molecule.

Alleles↗
PubMed1996

Analysis of meningococcal serogroup C-specific antibody levels in British Columbian children and adolescents.

The effects of age, sex, and possible prior exposure to serogroup C meningococci on group C-specific antibody levels (total and functional) were examined in 2- to 19-year-olds just before and 1 and 12 months after immunization with divalent (groups A + C) meningococcal capsular polysaccharide vaccine. Only age was found to have a significant effect on antibody levels. At 1 month, only 50% of 2- to 6-year-olds had detectable serum bactericidal antibody, in contrast to 84.1% and 96.3% of 9- to 12- and 13- to 19-year-olds respectively. By 12 months, only 20%, 40.9%, and 53.8% of subjects in these age groups had serum bactericidal antibody, suggesting that current meningococcal C polysaccharide vaccines provide only short-term protection. However, the drop in total specific antibody levels (by EIA) was less pronounced. Persistence of antibodies detectable by EIA (but not serum bactericidal antibodies) suggests that this vaccine may also give rise to antibodies of low affinity or directed to nonfunctional (nonprotective) epitopes (or both).

Adolescent↗
PubMed1996

Characterization of the HLA-restrictive elements of a rubella virus-specific cytotoxic T cell clone: influence of HLA-DR4 beta chain residue 74 polymorphism on antigenic peptide-T cell interaction.

The influence of glutamic acid (E)-alanine (A) dimorphism at position 74 of the DR4 beta chain on cytotoxic T cell recognition of an antigenic rubella virus peptide, E1(273-284), was studied using a panel of B cell lines and B cell transfectants expressing different HLA-DRB1 alleles as antigen-presenting cells and targets in 51Cr-release assays. Only B cell lines expressing the DRB1*0403, DRB1*0406 or DRB1*0407 subtypes which shared a residue, E, at position 74 in the DR4 beta chain when sensitized with E1(273-284) elicited strong cytotoxic T lymphocyte responses. However, in direct binding and antibody inhibition assays, it was shown that biotinylated E1(272-285) could bind to DR molecules with residues other than E at position 74, including DRB1*0401, DRB1*0404 and DRB1*1101 expressed on transfectants. E1(272-285) bound with similar affinity to the transfectant with DRB1*0403, which has E at position 74, as well as the transfectant with DRB1*0404, which does not. When T-B cell engagement rates were compared in cell conjugate assays, the percentage of T-B conjugates was higher when peptide-pulsed transfectants with DRB1*0403 were used than with transfectants expressing DRB1*0404. Hence, the HLA DR beta 1 polymorphism at position 74, while not critical for the binding affinity of E1(272-285) to the HLA molecule, appears to be a primary determinant of restricted recognition and subsequent activation of the peptide-specific T cells.

Amino Acid Sequence↗
PubMed1996

Lipomatous meningioma: characteristic computed tomographic appearance.

A case of lipomatous meningioma is reported. This is a rare variant of meningioma in which metaplasia of meningoepithelial cells occurs and mature adipocytes are present within the tumour. The heterogeneous attenuation and heterogeneous enhancement visualized on computed tomography (CT) can mimic necrotic malignant tumours. However, the demonstration of fat attenuation within the tumour explains the heterogeneity and suggests a benign process. The differential diagnosis of an extra-axial fat-containing tumour should include lipomatous meningioma.

Adipose Tissue↗
PubMed1996

Rubella reimmunization: comparative analysis of the immunoglobulin G response to rubella virus vaccine in previously seronegative and seropositive individuals.

Rubella virus (RV)-specific immunoglobulin G (IgG) antibodies were studied in military recruits undergoing unselected immunization with live attenuated measles, mumps, and rubella virus (MMR) vaccine. Three different whole-RV enzyme immunoassays (EIAs) and an epitope-specific EIA with a synthetic peptide (BCH-178c) representing a heutralization domain on the RV E1 envelope protein were used. Before vaccination, 84.2, 87.7, and 84.5% of the subjects tested (n = 399) were found to be seropositive (> 10 IU/ml or assay equivalent) by the three whole-RV EIAs, respectively, while only 82.5% were seropositive by the BCH-178c EIA. Although prevaccination seropositivity rates were similar for the whole-RV EIAs (sensitivity, 94 to 100%), many sera considered seropositive by the whole-RV EIAs had E1 peptide EIA antibody levels of < 10 IU/ml (sensitivity, 77.4 to 80.7%). One month after vaccination, 97.8, 97.2, and 93.5% of the subjects who were followed (n = 356) were seropositive by the three whole-RV EIAs, respectively, while 89% had BCH-178c peptide-specific IgG titers of > 10 IU/ml. After vaccination, depending on the assay used, up to 20.6% of initially seropositive individuals exhibited a greater than fourfold increase in RV-specific IgG, while up to 47.3% showed a greater than twofold increase. Increased antibody titers after vaccination (seroboosting) were most frequently associated with low levels of BCH-178c peptide-specific IgG before vaccination. RV protein-specific IgG was also studied by immunoblot assays in a subset (n = 56) of individuals receiving the MMR vaccine. Of these, 89.4 and 91.1% exhibited RV protein (E1, E2, and C protein)-specific IgG before and after vaccination, respectively. Seroboosting (two- to fourfold increase in EIA titers of individuals seropositive by the whole-RV EIA before vaccination) was usually accompanied by a shift in the IgG immunoblot pattern from a single (E1) to multiple (E1-E1, E1-C, or E1-E2-C) specificities, suggesting exposure of new epitopes as a result of viral replication.

Adolescent↗
PubMed1994

Analysis of overlapping T- and B-cell antigenic sites on rubella virus E1 envelope protein. Influence of HLA-DR4 polymorphism on T-cell clonal recognition.

A CTL antigenic site located between residues 273 and 291 of the E1 envelope protein of RV was identified by 51Cr-release assays employing SPs. Two E1-specific CTL clones were examined for immune recognition of RV wild-type and attenuated vaccine strains and recombinant E1 protein. The exact sequence (273-284) recognized by both clones was delineated by using truncated and overlapping SPs covering these residues. The defined T-cell site overlapped almost completely with a virus neutralizing antibody-binding site previously identified with mouse monoclonal and human antibodies. A series of single aa-substituted SP analogues of E1(273-284) was used to define residues critical for T-cell recognition. Using EBV-BL displaying different HLA-DR haplotypes and -DR4 subtypes as targets to determine MHC class II restriction elements, immune recognition by both T-cell clones was shown to be associated with HLA-DR4. Three HLA-DR4 subtypes (DR4Dw13A, DR4Dw13B, and DR4KT2) sharing a common residue, glutamic acid at position 74 in their beta 1 chains, were able to present SP E1(273-284) to the T-cell clones.

Amino Acid Sequence↗
PubMed1994

Use of synthetic peptides to map regions of rubella virus capsid protein recognized by human T lymphocytes.

Synthetic peptides (SPs), 18-29 amino acids long, representing selected sequences of rubella virus (RV) capsid (C) protein were used in lymphocyte proliferation assays to identify antigenic regions recognized by T lymphocytes from healthy RV-reactive adults. Four SPs, C(1-29), C(90-114), C(108-134) and C(255-300), stimulated proliferation of peripheral blood mononuclear cells and RV-specific T-cell lines from the same donors. C(1-29V), an SP analogue containing an RA27/3 RV vaccine strain sequence, stimulated higher levels of proliferation in T cells obtained from RV-vaccinated subjects than did the comparable wild-type (M33 strain) RV sequence.

Adult↗
PubMed1994

A simple simulation for the visualisation of CSF flow in infants with hydrocephalus.

Cerebrospinal fluid (CSF) flow was demonstrated incidentally in our unit during the routine cranial colour Doppler examination of infants with hydrocephalus. Pulsed Doppler analysis of the flow jets within CSF has shown that for each CSF flow jet there is a characteristic sinusoidal wave pattern that decreases in amplitude at the end of each jet episode. Any activity that transiently elevates the intracranial pressure, such as crying, increased the intensity of this signal. A study was subsequently carried out to investigate the origin of these clinical observations of CSF flow. Using a simple flow phantom, experiments with degassed water demonstrated the transient production of a Doppler signal at a stenosis in an otherwise uniform bore tube. We postulate that in infants with obstructive hydrocephalus, high CSF velocities in excess of 25 cm/s are produced as a result of the pressure caused by the excess cerebrospinal fluid. In some instances fluid jets may give rise to the production of microbubbles that act as transient but extremely efficient reflectors for the ultrasound, thus enabling the visualisation of CSF flow in these patients.

Cerebrospinal Fluid↗
PubMed1994

Predicting total weight of retail-ready lamb cuts from bioelectrical impedance measurements taken at the processing plant.

Data of sixty finished, crossbred lambs were used to develop prediction equations of total weight of retail-ready cuts (SUM). These cuts were the leg, sirloin, loin, rack, shoulder, neck, riblets, shank, and lean trim (85/15). Measurements were taken on live lambs and on both hot and cold carcasses. A four-terminal bioelectrical impedance analyzer (BIA) was used to measure resistance (Rs, ohms) and reactance (Xc, ohms). Distances between detector terminals (L, centimeters) were recorded. Carcass temperatures (T, degrees C) at time of BIA readings were also recorded. The equation predicting SUM from cold carcass measurements (n = 53, R2 = .97) was .093 + .621 x weight-.0219 x Rs + .0248 x Xc + .182 x L-.338 x T. Resistance accounted for variability in SUM over and above weight and L (P = .0016). The above equation was used to rank cold carcasses in descending order of predicted SUM. An analogous ranking was obtained from a prediction equation that used weight only (R2 = .88). These rankings were divided into five categories: top 25%, middle 50%, bottom 25%, top 50%, and bottom 50%. Within-category differences in average fat cover, yield grade, and SUM as a percentage of cold carcass weight of carcasses not placed in the same category by both prediction equations were quantified with independent t-tests. These differences were statistically significant for all categories except middle 50%. This shows that BIA located those lambs that could more efficiently contribute to SUM because a higher portion of their weight was lean.

Abattoirs↗