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J van Bergen

Publications and source records attributed to J van Bergen.

15 recordsLinked to original sources
PubMed2006

An improved RT-PCR method for the detection of killer-cell immunoglobulin-like receptor (KIR) transcripts.

Killer cell immunoglobulin-like receptors (KIRs) are expressed on human natural killer (NK) cells and a proportion of T cells. As the specificity of these NK and T cells is, at least in part, determined by the combination of KIRs they express, it is important to be able to determine the KIR expression pattern of NK and T cell clones to understand their function. However, for most KIR genes, specific reagents to detect expression are currently either unavailable or sensitive to allelic variations. In this study, a reverse transcriptase-polymerase chain reaction (RT-PCR) that uses new primer sets for the gene-specific detection of KIR transcripts is presented and validated. The key advantage of this RT-PCR method over previously published ones is that it was designed to detect transcripts of all confirmed allelic variants of the KIR genes, while remaining gene-specific.

Animals↗
PubMed2006

Prevalence of urogenital Chlamydia trachomatis infections in the Netherlands suggests selective screening approaches. Results from the PILOT CT Population Study.

Chlamydia trachomatis screening is being considered in the Netherlands, but policy recommendations are hampered by the lack of population-based data. We studied the prevalence of chlamydia infection in 15-29-year-old women and men in a national representative sample of 21,000 inhabitants of rural and urban areas in the Netherlands. Of this sample, 41% responded by sending in urine and an answered questionnaire, while 11% returned a refusal card. The overall prevalence of chlamydia infection was 2.0% (CI: 1.7-2.3); 2.5% (CI: 2.0-3.0) in women and 1.5% (1.1-1.8) in men. Chlamydia prevalence was significantly greater in very highly urbanized areas (3.2%, CI: 2.4-4.0) compared to rural areas (0.6%, CI: 0.1-1.1). In very highly urbanized areas the greatest prevalence was found among 15-19-year-old women (4.3%) and among 25-29-year-old men (4.2%). A risk profile could be determined and a prediction rule was developed. These data suggest that nationwide systematic screening is not indicated in the Netherlands and that targeted approaches are a better option. Roll-out of selective screening is recommended.

Adolescent↗
PubMed2005

Prevalence of urogenital Chlamydia trachomatis increases significantly with level of urbanisation and suggests targeted screening approaches: results from the first national population based study in the Netherlands.

OBJECTIVES: Chlamydia trachomatis (Chlamydia) is the most prevalent sexually transmitted bacterial infection and can cause considerable reproductive morbidity in women. Chlamydia screening programmes have been considered but policy recommendations are hampered by the lack of population based data. This paper describes the prevalence of Chlamydia in 15-29 year old women and men in rural and urban areas, as determined through systematic population based screening organised by the Municipal Public Health Services (MHS), and discusses the implications of this screening strategy for routine implementation. METHODS: Stratified national probability survey according to "area address density" (AAD). 21 000 randomly selected women and men in four regions, aged 15-29 years received a home sampling kit. Urine samples were returned by mail and tested by polymerase chain reaction (PCR). Treatment was via the general practitioner, STI clinic, or MHS clinic. RESULTS: 41% (8383) responded by sending in urine and questionnaire. 11% (2227) returned a refusal card. Non-responders included both higher and lower risk categories. Chlamydia prevalence was significantly lower in rural areas (0.6%, 95% CI 0.1 to 1.1) compared with very highly urbanised areas (3.2%, 95% CI 2.4 to 4.0). Overall prevalence was 2.0% (95% CI 1.7 to 2.3): 2.5% (95% CI 2.0 to 3.0%) in women and 1.5% (95% CI 1.1 to 1.8) in men. Of all cases 91% were treated. Infection was associated with degree of urbanisation, ethnicity, number of sex partners, and symptoms. CONCLUSION: This large, population based study found very low prevalence in rural populations, suggesting that nationwide systematic screening is not indicated in the Netherlands and that targeted approaches are a better option. Further analysis of risk profiles will contribute to determine how selective screening can be done.

Adolescent↗
PubMed2001

Induction of antigen specific CD4+ T cell responses by invariant chain based DNA vaccines.

In this report, the use of DNA vaccination to induce class II restricted antigen specific proliferative responses was studied. To this end, a construct encoding the invariant chain (Ii) was engineered in which the Class II associated invariant chain peptide (CLIP) sequence was replaced by an immunogenic epitope derived form Heat Shock Protein 60, HSP60 178-186. Transfection studies in vitro showed that this construct can be used to efficiently load MHC class II molecules and present epitopes to MHC class II restricted antigen specific T cells. In addition, we showed that intradermal immunisation of Lewis rats with these constructs induced antigen specific T cells in vivo. Therefore, our Ii-gene constructs can be used to immunise for defined CD4+ T cell epitope sequences.

Amino Acid Sequence↗
PubMed2001

CD4-independent T cells impair TCR triggering of CD4-dependent T cells: a putative mechanism for T cell affinity maturation.

In vivo, T cells expressing low-affinity TCR predominate in primary, but not in secondary responses, a process referred to as T cell affinity maturation. Using CD4 dependence as a measure of the avidity of the interaction between the allospecific TCR and the alloantigen, we show that a similar process occurs in mixed lymphocyte cultures in vitro. Moreover, in coculture experiments high-avidity (CD4-independent) T cell clones inhibited the TCR internalization of low-avidity (CD4-dependent) T cell clones, whereas low-avidity T cell clones had no such effect on high-avidity T cell clones. The extent of inhibition of TCR internalization was dependent on both the avidity of the competing clone and the number of competing cells. Thus, there was a cell dose- and avidity-dependent effect on TCR internalization, an early parameter in T cell activation. These results suggest that low- and high-avidity T cell clones compete for the availability of antigen-presenting cells and that this favors the selective outgrowth of high-avidity T cell clones.

CD3 Complex↗
PubMed2000

Superior tumor protection induced by a cellular vaccine carrying a tumor-specific T helper epitope by genetic exchange of the class II-associated invariant chain peptide.

Efficient loading of MHC class II molecules with a T helper epitope of choice can be achieved through genetic exchange of the MHC class II-associated invariant chain peptide (CLIP) sequence with a sequence encoding the helper peptide. We have now used this method to engineer a cellular vaccine that continuously expresses a tumor-specific helper epitope in a defined costimulatory context. We provide evidence (a) that this cellular vaccine induces peptide-specific helper T cells in vivo that are functional in protecting mice from challenge with a highly aggressive tumor, (b) that this vaccine can directly prime tumor-specific helper T cells in vivo, and (c) that this cellular vaccine is superior compared with similar cells loaded with synthetic T helper peptide in inducing tumor protection. In conclusion, cellular vaccines for activation of antigen-specific helper T cells can be greatly improved by the introduction of invariant chain constructs containing a T helper epitope by class II-associated invariant chain peptide exchange.

Amino Acid Sequence↗
PubMed2000

Identification of a novel tumor-specific CTL epitope presented by RMA, EL-4, and MBL-2 lymphomas reveals their common origin.

C57BL/6 mice generate a vigorous H-2Db-restricted CTL response against murine leukemia virus (MuLV)-induced tumors. For many years it has been suggested that this response is directed to an MuLV-encoded peptide as well as to a nonviral tumor-associated peptide. Recently, a peptide from the leader sequence of gag was demonstrated to be the MuLV-derived epitope. Here we describe the molecular identification of the tumor-associated epitope. Furthermore, we show that the CTL response against this epitope can restrict the outgrowth of MuLV-induced tumors in vivo. The epitope is selectively presented by the MuLV-induced T cell tumors RBL-5, RMA, and MBL-2 as well as by the chemically induced T cell lymphoma EL-4. Intriguingly, these tumors share expression of the newly identified epitope because they represent variants of the same clonal tumor cell line, as evident from sequencing of the TCR alpha- and beta-chains, which proved to be identical. Our research shows that all sources of RBL-5, RMA, RMA-S, MBL-2, and EL-4 tumors are derived from a single tumor line, most likely EL-4.

Adoptive Transfer↗
PubMed1999

A BCR-ABL oncoprotein p210b2a2 fusion region sequence is recognized by HLA-DR2a restricted cytotoxic T lymphocytes and presented by HLA-DR matched cells transfected with an Ii(b2a2) construct.

Peptides corresponding to the fusion site in 210 kD BCR-ABL protein b3a2 (p210b3a2) were previously shown to bind to several HLA class I and II alleles. We have found that b3a2 peptide-specific CD4-positive T-helper cells were able to recognize p210b3a2-positive chronic myelogenous leukemia (CML) blasts in a DR4 restricted manner. Until now, there were no reports of b2a2 breakpoint-specific human T-cell responses. Here we show that repetitive stimulation of T lymphocytes with a 17mer peptide covering the fusion region in p210b2a2 also leads to specific T-cell responses. CD4 and CD4/CD8 double-positive clones obtained from a b2a2 peptide-specific cell line were cytotoxic and proliferative in an HLA-DR2a (DRB5*0101) restricted fashion. Autologous Epstein-Barr virus (EBV) transformed cells, expressing BCR-ABL(b2a2) on transfection, and allogeneic HLA-DR matched p210b2a2-positive cells from CML patients were, however, not lysed. BCR-ABL peptide-specific T-cell clones did respond to autologous EBV cells transfected with invariant chain (li) cDNA in which the HLA class II-associated invariant chain peptide (CLIP) was replaced by a BCR-ABL b2a2 fusion oligonucleotide sequence, illustrating the potential of these T cells to recognize an endogenous BCR-ABL(b2a2) ligand.

Antigen Presentation↗
PubMed1999

Get into the groove! Targeting antigens to MHC class II.

The activation of MHC class II-restricted helper T cells is paramount to adaptive immune responses. Vaccine development could therefore benefit from improved ways of targeting antigens into MHC class II molecules. In recent years, the natural pathways of MHC class II antigen presentation have been exploited to achieve this goal. First, antigenic proteins and peptides have been modified to facilitate receptor-mediated uptake by professional antigen-presenting cells. Second, DNA constructs containing specific targeting sequences have been used to direct endogenously synthesized antigens to the MHC class II compartments. Both strategies proved to be highly effective. We review these data and describe how this knowledge is currently applied to the design of vaccines that activate helper T cells in vivo.

Amino Acid Sequence↗
PubMed1998

Altered peptide ligands and wild-type peptide induce indistinguishable responses of a human Th0 clone.

The response of the human influenza hemagglutinin (HA)-specific T helper clone HA1.7 to its wild-type (wt) HA307-319 peptide ligand and related altered peptide ligands (APL) was examined over a wide range of antigen concentrations. The time course of cytokine production and surface expression of CD40 ligand and CD3 was followed at the single-cell level by flow cytometry and compared with the induction of proliferation. We observed that the APL induced responses that were indistinguishable from those induced by the wt HA ligand, albeit at higher antigen densities. Moreover, the activation parameters were induced with identical kinetics. Blocking of CD4 co-ligation inhibited the recognition of the weakly stimulatory APL, but not of the wt HA307-319 peptide. Finally, in all cases the response of the T cell clone correlated with down-regulation of surface TCR/CD3 complexes. Together, these observations support a quantitative model of T cell activation.

Amino Acid Sequence↗
PubMed1997

Efficient loading of HLA-DR with a T helper epitope by genetic exchange of CLIP.

The HLA class II-associated invariant chain (Ii)-derived peptide (CLIP) occupies the peptide binding groove during assembly in the endoplasmic reticulum, travels with HLA class II to endosomal compartments, and is subsequently released to allow binding of antigenic peptides. We investigated whether the exchange of CLIP with a known T helper epitope at the DNA level would lead to efficient loading of this helper epitope onto HLA class II. For this purpose, a versatile Ii-encoding expression vector was created in which CLIP can be replaced with a helper epitope of choice. Upon supertransfection of HLA-DR1-transfected 293 cells with an Ii vector encoding a known T helper epitope (HA307-319), predominantly length variants of this epitope were detected in association with the HLA-DR1 molecules of these cells. Moreover, this transfectant was efficiently recognized by a peptide-specific T helper clone (HA1.7). The results suggest that this type of Ii vector can be used to create potent class II+ cellular vaccines in which defined T cell epitopes are continuously synthesized.

Amino Acid Sequence↗
PubMed1994

Usage of TCRAV and TCRBV gene families in human fetal and adult TCR rearrangements.

We have investigated fetal and adult T-cell receptor (TCR) A and B V-gene repertoires both by fluorescence-activated cell sorter (FACS) analysis with the available TCR V region-specific mAbs and by the polymerase chain reaction (PCR) with TCR V gene family-specific oligonucleotides. Among the low number of CD3+ T cells, most of the TCR V regions tested for could be detected by FACS analysis in liver, bone marrow, and spleen derived from a 14-week-old fetus and two 15-week-old fetuses. Similarly, the PCR analysis showed that the majority of the TCRAV and TCRBV families were expressed in the peripheral organs of the 13-week-old fetus, although an apparent absence of particular TCR V families was found in liver and bone marrow. This was most probably the consequence of the low number of CD3+ T cells in these organs. In 17-week-old fetal thymi the level of expression of some TCRAV and TCRBV gene families, in particular those that contain a single member, was lower compared to post-partum thymi and adult peripheral blood mononuclear cells. The combined data of FACS and PCR analysis demonstrate that TCR V genes belonging to the majority of TCR V gene families can be used in TCR alpha and beta chain rearrangements during early human fetal life. Our data also suggest that the expression levels of some of the single member TCR V gene families may be influenced by the developmental stage.

Animals↗
PubMed1992

Flow resistance of coaxial breathing systems: investigation of a circuit disconnect.

A clinical incident involving an undetected disconnection occurred during the use of a CPRAM coaxial breathing circuit. The flow resistance of this circuit was evaluated and compared with that of a Bain circuit to determine the factors involved. A differential pressure transducer was used to monitor the pressure drop across each circuit during simulation of controlled ventilation with a fresh gas flow of 6 L.min-1. An Ohio V5 anaesthesia ventilator was adjusted to different flow rates and tidal volumes and a test lung simulated an airway resistance of 2.7 cm H2O.L-1.sec and a compliance of 0.05 L.cmH2O-1. Absolute pressure at the ventilator was also monitored when the circuit was disconnected from the test lung. The CPRAM circuit displayed a pressure drop from the ventilator to the endotracheal tube of 6.3 cm H2O at 60 L.min-1, about twice that found with the Bain. A disconnection at the tracheal connector produced an absolute pressure at the ventilator of 9.6 cm H2O with the CPRAM and 5.5 cm H2O with the Bain. Since the ventilator low pressure alarm was preset to 9.2 cm H2O, the alarm provided a warning with the Bain but not the CPRAM. The elevated flow resistance of the CPRAM circuit was attributed to a restriction in the flow area at the patient end of the circuit. Capnographs or adjustable low-pressure alarms provide more reliable monitoring for breathing circuit disconnects.

Anesthesia, Closed-Circuit↗