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Biomedical subjects

H Chan

Publications and source records attributed to H Chan.

At least 145 records · Page 8Linked to original sources
PubMed1986

Plicatic acid-specific IgE and nonspecific bronchial hyperresponsiveness in western red-cedar workers.

In a cross-sectional survey of 652 workers in a western red-cedar sawmill, we obtained data on symptoms, pulmonary function, immediate skin reactivity to common allergens, nonspecific bronchial responsiveness, total IgE level, and sensitization to plicatic acid conjugated with human serum albumin as measured by RAST. Dust exposure was estimated by personal and area sampling for total dust during a work shift and cumulative exposure by duration of employment. Seven percent of the workers had an elevated RAST, and 20% had nonspecific bronchial hyperresponsiveness. Elevation in RAST was associated with bronchial hyperresponsiveness. Almost half (46%) of the workers with RAST elevation had bronchial hyperresponsiveness compared to 18% in workers with no RAST elevation. The association was unaffected by total IgE level or by limiting the analysis to workers without respiratory symptoms and was most apparent in younger workers. Bronchial hyperresponsiveness was associated with increased prevalence of respiratory symptoms as well as with lower levels of pulmonary function. The likelihood of bronchial hyperresponsiveness increased with increasing age but was unrelated to the dust-exposure concentration. RAST elevation was unrelated to employment duration or dust exposure and was not associated with an increased prevalence of symptoms or lower levels of pulmonary function independent of bronchial hyperresponsiveness. We conclude that plicatic acid-specific IgE and nonspecific bronchial hyperresponsiveness are associated in western red-cedar workers and that this association may reflect a causal connection.

Adult↗
PubMed1986

Occupational asthma caused by eastern white cedar (Thuja occidentalis) with demonstration that plicatic acid is present in this wood dust and is the causal agent.

A worker developed symptoms of work-related asthma a few weeks after starting to work in a sawmill where eastern white cedar (Thuja occidentalis) was transformed into shingles. The diagnosis of occupational asthma was confirmed by monitoring of peak expiratory flow rates and bronchial responsiveness to histamine off work and at work, and specific inhalation challenges in the laboratory that demonstrated an isolated late asthmatic reaction after exposure for 4 hours to the wood dust. Specific inhalation challenges with western red cedar (thuja plicata) for 2 hours and plicatic acid (PA) for 7 minutes also caused an isolated late asthmatic reaction. Elevated specific IgE levels to PA were present. Antiserum was produced in rabbits that were immunized with PA conjugated to human serum albumin. With this antiserum in inhibition experiments, cross-reactivity between western red cedar and eastern white cedar, both belonging to the family of arborvitae, was found. It is estimated that eastern white cedar contains approximately half the amount of PA present in western red cedar.

Adult↗
PubMed1986

A general method for retrieving the components of a genetically engineered fusion protein.

Escherichia coli expression vectors encoding an acid-labile aspartyl-proline (Asp-Pro) dipeptide bridging two protein sequences were constructed and used to synthesize two different bovine growth hormone (bGH) fusion proteins. The codons GAT-CCX coding for Asp-Pro are provided by the recognition site for Bam HI (GGATCC). Treatment of the bGH fusion proteins at low pH in the presence of guanidine hydrochloride releases the bGH moiety from the fusion protein. The release of the bGH from the fusion protein specifically requires the Asp-Pro dipeptide linking the bGH sequence to the fusion protein. The bGH released from the fusion protein retains anti-bGH immunoreactivity as well as the ability to bind to growth hormone receptor in vitro.

Acids↗
PubMed1985

Intermittent myelination of small-diameter sciatic axons in Xenopus laevis.

Nerve fibres from the sciatic nerve of apparently normal Xenopus laevis were examined in teased preparations of living material and in series of cross-sections. Small-diameter fibres were found that were myelinated in a spatially intermittent fashion. In these fibres, the myelinated segments were separated by long non-myelinated regions that had a 1 : 1 relationship to the investing Schwann cell. It is estimated that at least 10% of the myelinated fibres with an external diameter of less than 5 micrograms were intermittently myelinated.

Animals↗
PubMed1985

A study of serum antibody activity in workers with occupational exposure to diphenylmethane diisocyanate.

The prevalence of sensitization was studied in a group of 76 foundry workers with occupational exposure to diphenylmethane diisocyanate (MDI). Ten workers had clinical evidence of asthma, 40 had non-asthmatic respiratory symptoms, and 26 were asymptomatic. Specific IgE antibodies to MDI were found in two workers (2.6%) and specific IgG antibodies, in five workers (6.6%). The prevalence of IgE and IgG antibodies was higher in the 10 subjects with asthma than in the non-asthmatic group. The prevalence of anti-paratolyl-monoisocyanate antibodies was not significantly different from that of anti-MDI antibodies, and both haptenic determinants displayed a high degree of cross-reactivity in the RAST inhibition test. The role of humoral immunological mechanisms in MDI-induced asthma is unclear in view of the rather low prevalence of these serum antibodies in this group of workers.

Antibodies↗
PubMed1984

Binocular summation on fused annular backgrounds.

A paradigm has been proposed to test the hypothesis that binocular fusion results in simple summation, S, of monocular photopic luminances: S = delta LBM(L)/delta LB(2L) = 1, where delta LBM and delta LB are threshold luminances for a monocular and a binocular increment, appearing on a fused background of luminance L or 2L, respectively. This prediction was tested psychophysically, with background size as parameter. Thresholds were measured for a brief (20 ms) foveal flash centered on a luminous disk encircled by a massive black annulus serving as a fusion lock. The flash was presented binocularly, or monocularly, at 30 and 60 cd m-2 background luminances. The diameter of the disk was varied from 3 min to 40 min visual angle. The size of the flash was constant (6 min diameter), except for the smallest disk (3 min diameter). All thresholds varied as a function of background size (the known 'sensitization effect'). The summation index S did not vary with background size. A mean value S = 0.9 was found; this is consistent with the notion that summation of the order of 90% occurs during binocular fusion. We surmise that even a weak monocular test flash makes fusion less than perfect.

Adult↗
PubMed1984

Baker's asthma. Studies of the cross-antigenicity between different cereal grains.

Specific IgE antibodies were demonstrated in the sera of six bakers with respiratory symptoms of asthma or bronchitis by the radioallergosorbent (RAST) assay. The specificity of the antibodies was found to be directed not only against the common flours (rye, wheat) used in the bakeries but also against triticale, barley, oat, corn and rice in some of the bakers. By using the RAST inhibition tests, cross-antigenicity was shown to exist between different cereal grains. The degree of cross-reactivity closely paralleled their taxonomic relationship and appeared to be in the following order of decreasing closeness: wheat, triticale, rye, barley, oat, rice and corn. The allergenic activity in the rye and wheat extracts was found to be distributed among various fractions of different molecular weights.

Antibodies, Anti-Idiotypic↗
PubMed1983

Relationship between types of asthmatic reaction, nonspecific bronchial reactivity, and specific IgE antibodies in patients with red cedar asthma.

We studied the relationship between specific IgE antibodies, nonspecific bronchial reactivity to methacholine, and the type of asthmatic reaction in patients with red cedar asthma. The level of circulating specific IgE antibodies (expressed as RAST ratios) was not related to the type of asthmatic reaction, the degree of nonspecific bronchial hyperreactivity [expressed by the provocative concentration of methacholine producing a 20% decrease in the forced expiratory volume in 1 sec (PC20)] or the index of reactivity to plicatic acid. On the other hand, methacholine PC20 was found to correlate with the index of reactivity to plicatic acid in the late asthmatic reaction (LAR) and both the immediate and late components of the dual asthmatic reaction (DAR). Development of the LAR is associated with increase in nonspecific bronchial hyperreactivity. Repeated inhalation challenge with plicatic acid in eight patients with LAR resulted in DAR in all. The results suggest that the mechanism responsible for the LAR is associated with an increase in nonspecific bronchial reactivity; furthermore, the immediate component of DAR could also be related to heightened bronchial hyperreactivity.

Adult↗
PubMed1983

Baker's asthma. Clinical and immunological studies.

Seven bakers with respiratory symptoms were evaluated by skin tests, RAST assay for specific IgE antibodies to rye and wheat, inhalation challenge with methacholine for the determination of non-specific bronchial reactivity, and bronchoprovocation with rye and wheat extracts for the determination of antigen-specific bronchial reactivity. An immediate asthmatic response to antigen challenge was observed in four subjects and all of them had a high level of flour-specific IgE antibodies. The serum RAST values provided a more accurate predictive value than the degree of cutaneous sensitivity determined by skin testing with respect to the bronchial response to antigenic challenge. Among those who reacted positively to antigenic bronchoprovocation, a much lower antigen dose was required to elicit a positive reaction if the subject also had an increased degree of non-specific bronchial reactivity. An elevated RAST value was not found in thirty-eight asymptomatic bakers or in ten asthmatics who had no occupational exposure to flour. Thus, baker's asthma appears to be a form of allergic asthma to cereal flours mediated by specific IgE antibodies. Both the level of serum IgE antibodies and the degree of non-specific bronchial reactivity are important factors which may influence a baker's bronchial response upon inhalation of cereal flours.

Adult↗
PubMed1983

Asthma caused by diphenylmethane diisocyanate in foundry workers. Clinical, bronchial provocation, and immunologic studies.

Eleven foundry workers who developed asthmatic symptoms were studied with inhalation provocation tests with formaldehyde and diphenylmethane diisocyanate (MDI). These latter two chemicals are components of PepSet used for making molds for casting. Six subjects showed specific asthmatic reactions to MDI challenge (more than 20% fall in FEV1), 2 had a combined immediate and late reaction, and 4 had a predominantly late reaction. Four of the 6 subjects experienced recurrent nocturnal asthmatic reactions after a single challenge with MDI that lasted as long as 7 days, and this was associated with a significant increase in bronchial reactivity to methacholine. One subject had an immediate irritant reaction to both MDI and formaldehyde, which was spontaneously reversed in a few minutes. None of the remaining 10 subjects had a positive reaction to formaldehyde challenge. The reactors to MDI showed more evidence of air-flow obstruction in their lung function measurements and had a greater bronchial sensitivity to methacholine than the nonreactors but there was no difference in age, smoking habits, or atopic status. Specific IgE antibodies to MDI-human serum albumin conjugate were detected in 2 subjects, a reactor and a nonreactor. Specific IgG anti-MDI antibodies were detected in 4 subjects, 2 who reacted and 2 who did not. No difference in the pattern of response to MDI inhalation was observed in relation to the different immunologic findings. We conclude that MDI is a cause of asthma in foundry workers.

Age Factors↗
PubMed1982

Specific IgE antibodies in workers with occupational asthma due to western red cedar.

The presence of specific IgE antibodies in the serum of patients with occupational asthma resulting from exposure to western red cedar (RCA) was studied by a radioallergosorbent test (RAST). The antigen matrix used in the RAST was either a conjugate of Sepharose particles with antigens in a crude cedar extract or with plicatic acid, the major haptenic component of cedar antigens. Of eighteen patients with clinical RCA and positive reaction to antigenic bronchoprovocation, eight were found to have abnormal RAST values. By appropriate absorption experiments, the serum RAST activity was shown to represent cedar antigen-specific IgE antibodies. No significant RAST activity was detected in the serum specimens from sixteen control subjects or from ten patients with negative bronchoprovocation-reaction to antigenic challenge. These results suggest that IgE antibody-mediated allergic reaction may be an important pathogenetic factor in RCA.

Allergens↗
PubMed1982

Hodgkin's disease in children: treatment results with MOPP and low-dose, extended-field irradiation.

Combined therapy with MOPP and extended-field irradiation for all children with Hodgkin's disease (except those with favorable clinical stage [CS] 1) was effective in disease control. Overall 5-year survival and relapse-free survival rates were 92% and 82%, respectively. Only one of 27 CS 2 and 3 patients has relapsed (median followup, 4.3 years). Two patients in complete remission died of viral infection. The cost-benefit ratio for such treatment remains to be determined. Morbidity was decreased by the omission of staging laparotomy with splenectomy and by reduction in radiation dose and to a lesser extent volume, but it was increased by the addition of MOPP. In such combined treatment, the smallest number of cycles of MOPP, the lowest radiation dose, and the smallest radiation volume that may be used without loss of treatment effectiveness remain to be determined.

Adolescent↗
PubMed1980

Inverted terminal repetition in vaccinia virus DNA encodes early mRNAs.

Vaccinia virus DNA contains a long inverted terminal repetition of MW approximately 6.8 x 10(6). A fragment of MW 6.3 X 10(6) from this repetition has been cloned in coliphage lambda and used to isolate RNA from virus-infected cells. Electron microscopy indicates that early RNAs are transcribed from the repeated sequence and cell-free translation shows that the RNAs code for polypeptides.

Bacteriophage lambda↗
PubMed1978

Activity patterns of human skeletal muscles: relation to muscle fiber type composition.

The muscle activity of normal ambulatory individuals was recorded continuously for 8-hour (working day) periods. Parameters of activity patterns were defined and numerical outcomes for these parameters were compared across a diverse population of muscles. Several pattern parameters, such as the average percentage of time active, were highly correlated with the percentage of type I fibers of a muscle.

Adult↗