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Biomedical subjects

C Verweij

Publications and source records attributed to C Verweij.

9 recordsLinked to original sources
PubMed2001

Antigenic and molecular heterogeneity in recent swine influenza A(H1N1) virus isolates with possible implications for vaccination policy.

In order to explore the occurrence of antigenic drift in swine influenza A(H1N1) viruses and the match between epidemic and vaccine strains, 26 virus isolates from outbreaks of respiratory disease among finishing pigs in the Netherlands in the 1995/1996 season and reference strains from earlier outbreaks were examined using serological and molecular methods. In contrast to swine H3N2 viruses, no significant antigenic drift was observed in swine H1N1 viruses isolated from the late 1980s up to 1996 inclusive. However, a marked antigenic and genetic heterogeneity in haemagglutination inhibition tests and nucleotide sequence analyses was detected among the 26 recent swine H1N1 virus strains. Interestingly, the observed antigenic and molecular variants were not randomly distributed over the farms. This finding indicates independent introductions of different swine H1N1 virus variants at the various farms of the study and points to a marked difference between the epidemiologies of human and swine influenza viruses. The observed heterogeneity may hamper the control of swine influenza by vaccination and indicates that the efficacy of current swine influenza vaccines requires re-evaluation and that the antigenic reactivity of swine influenza viruses should be monitored on a regular basis.

Animals↗
PubMed1999

Antigenic drift in swine influenza H3 haemagglutinins with implications for vaccination policy.

In order to explore the occurrence of antigenic drift in swine influenza A(H3N2) virus, we examined virus strains from outbreaks of respiratory disease among finishing pigs in the Netherlands in 1996 and 1997 and from earlier outbreaks. In contrast to swine H3N2 strains from the 1980s, the recent isolates did not show significant cross-reactivity with human influenza A(H3N2) viruses from 1972-1975 in haemagglutination inhibition tests. These new strains form a separate branch in the phylogenetic trec of the HA1 parts of HA. We conclude that recently there has been considerable antigenic drift within the swine H3N2 viruses in the Netherlands and Belgium and recommend replacement of the A/Port Chalmers/1/73 (H3N2) strain in the current vaccine by a more recent swine H3N2 isolate.

Animals↗
PubMed1997

Characterization of complement C6 deficiency in a PVG/c rat strain.

Complement C6 plays an important role in the effector phase of complement-mediated cell lysis. Recently, a PVG/c rat strain deficient in haemolytic C6 activity was discovered. In the present study we show that these rats lack both antigenic and functional C6, and that repetitive immunization of these rats with PVG/c+ serum results in generation of specific anti-rat C6 antibodies. The observed absence of rat C6 was further investigated at the genomic and transcriptional level using a 492-bp cDNA of rat C6, cloned from a rat liver cDNA library using full length human C6 as a probe. Northern blot analysis revealed the presence of C6 mRNA in livers of both PVG/c- and PVG/c+ rats, corresponding to a size of approximately 3.3 kb, although the level of C6 mRNA expression was approximately 100-fold less in PVG/c- rats. In addition, using rat C6-specific primers, positive signals were obtained in kidneys of both rat strains by reverse transcriptase-polymerase chain reaction (RT-PCR) analysis. Southern blot analysis of digested genomic DNA did not reveal evidence for large C6 gene deletions. We conclude that the lack of C6 protein in the PVG/c- rat strain is not due to a (large) C6 gene deletion, but presumably is caused by an unstable mRNA or a point mutation in the C6 gene resulting in an aberrant transcription of the C6 gene. Alternatively, a gene coding for a product involved in C6 biosynthesis that acts in trans may carry a mutation.

Animals↗
PubMed1996

The tetracycline derivative minocycline differentially affects cytokine production by monocytes and T lymphocytes.

Minocycline is a tetracycline derivative that has beneficial effects in noninfectious forms of arthritis and dermatitis. To investigate whether this effect may be attributed to interference with cytokine production, we studied the effect of minocycline on cytokine production by T cells and monocytes. Minocycline exerted an inhibitory effect on tumor necrosis factor alpha (TNF-alpha) and gamma interferon production by stimulated T cells, whereas the production of interleukin 6 (IL-6) remained unaffected. The effect of minocycline on TNF-alpha mRNA synthesis by T cells was shown to be stimulus specific. T cells stimulated by a Ca2+-independent mode exhibited a decrease in TNF-alpha mRNA in the presence of minocycline, whereas the TNF-alpha mRNA level remained unaffected by minocycline when cells were stimulated in a Ca2+-dependent manner. In contrast to the effect on T cells, addition of minocycline to lipopolysaccharide-stimulated monocytes led to a dose-dependent increase in TNF-alpha and IL-6 production which was paralleled by an enhancement of TNF-alpha mRNA synthesis. These results indicate that minocycline exerts differential effects on the regulation of cytokine production by T cells and monocytes that are partly reflected at the mRNA level. Given the pleiotropic effects of minocycline, it is suggested that the immunostimulatory effect on monocytes might counteract its beneficial properties in the treatment of several forms of chronic inflammation.

Anti-Bacterial Agents↗
PubMed1990

Residual hearing capacity of severely hearing-impaired subjects.

Speech reception functions (speech reception threshold and maximum discrimination score for phonemes) and auditory functions (hearing threshold, difference limens for intensity and frequency, temporal modulation threshold function, critical ratio and temporal integration) have been investigated in a group of severely hearing-impaired subjects (64 ears, median Fletcher Index of 80 dB). The results were separated into low-, middle- and high-frequency regions. The investigations were intended to describe and quantify the residual hearing capacities and the correlations between the different functions. It was found that the speech functions, the difference limen for frequency, the critical ratio and the time constant of temporal integration deteriorate gradually with increasing hearing loss. These functions show a relatively high mutual correlation in the low-frequency region and considerable scatter in the high-frequency part. The sensitivity for modulations and the difference limen for intensity were least affected. The results revealed that the residual capacity can be described by means of two independent factors: frequency discrimination at the higher frequencies and a decrease in processing efficiency of the system. The latter is dominated by the middle- and low-frequency hearing elements.

Adolescent↗
PubMed1985

Investigations of the residual hearing capacity of severely hearing-impaired and profoundly deaf subjects.

Speech reception functions (maximum discrimination score for phonemes, speech reception threshold) and auditory functions (pure-tone audiogram, difference limens for frequency and intensity, temporal modulation transfer function, critical ratio and temporal integration) have been investigated in a group of severely hearing-impaired and deaf subjects (median Fletcher index: 80 dB), for different frequency regions (250, 1 000 and 2 000/4 000 Hz). The correlations between the different functions were calculated on the basis of characteristic numbers, derived from the originally measured functions, in the indicated frequency regions. The residual hearing capacities could be described best with two factors, one reflecting the distortion term in the speech reception threshold and the other representing the frequency discrimination for high-frequency tones. It was found that residual hearing capacities are present, at least up to a Fletcher index of 105 dB.

Adolescent↗
PubMed1984

Reliability of auditory function tests in severely hearing-impaired and deaf subjects.

The test-retest variability of a series of auditory functions has been investigated in a group of severely hearing-impaired and deaf subjects (64 ears, median Fletcher index: 80 dB) and in a group of 10 controls with normal hearing. An adaptive forced-choice procedure was used for both groups. The functions were: tone audiogram, difference limen for intensity, difference limen for frequency, modulation transfer function and critical ratio. In spite of sometimes strongly deviating function values within the hearing-impaired group, the test-retest variability of the two groups was found to be of the same order of magnitude, except for the tone audiogram where the variability in the hearing-impaired group was twice that for the control group.

Adolescent↗
PubMedDate not supplied

Electro-cochlear potentials elicited by sinusoidally modulated signals.

Responses of the guinea pig cochlea to amplitude-modulated stimuli were measured with the aid of a gross electrode. The dynamic characteristics of this part of the auditory system was studied by varying several parameters of the applied signal. The signals used as carriers in our experiments were either white noise or pure tones of 1 and 4 kHz. The modulation frequency, dynamic and intensity characteristics were determined by varying the modulating frequency, the modulation depth and the intensity of the applied signal. To get an idea about possible non-linear aspects of the system under investigation, we always computed the Fourier transform of the response data and plotted the amplitude of the various harmonics and the phase of the fundamental separately as functions of the signal parameter in question. The greatest response was always found at a modulation frequency of about 200 Hz, with a relatively gradual rise up to this frequency and a sharper drop above 200 Hz. The phase of the fundamental changes very rapidly at frequencies above Hz. The distortion is mainly second-harmonic and has a maximum about 1 octave lower than the fundamental. The carrier frequency and the intensity of the stimulus were not found to have a great influence on the frequency characteristic. For small modulation depths, the system is nearly linear; at higher intensities and modulation depths saturation occurs, coinciding with a relative increase in the intensity of the second harmonic with respect to the fundamental.

Acoustic Stimulation↗