Combined asthma and alveolitis due to diphenylmethane diisocyanate (MDI) with demonstration of no crossed respiratory reactivity to toluene diisocyanate (TDI)

Two workers, who developed asthmatic symptoms, were studied with inhalation provocation tests using diphenylmethane diisocyanate (MDI) and toluene diisocyanate (TDI). The subjects showed specific asthmatic reactions to MDI challenge (more than 20% fall in FEV1), and one also had an alveolar response. Alveolitis was suggested by fever, basal crackles, increased neutrophil counts in venous blood and in bronchoalveolar lavage. The asthmatic reaction to MDI challenge was associated with an increase in airway responsiveness to methacholine in both subjects. We conclude that MDI is a cause of asthma and/or hypersensitivity pneumonitis in workers exposed to diphenylmethane diisocyanate.     

Dexamethasone isonicotinate inhibits dual and late asthmatic reactions but not the increase of airway responsiveness induced by toluene diisocyanate in sensitized subjects

To determine whether treatment with aerosolized dexamethasone isonicotinate inhibits asthmatic reactions and the associated increase in airway responsiveness induced by toluene diisocyanate (TDI), we studied six sensitized subjects with previously demonstrated dual or late asthmatic reaction after inhalation challenge with TDI. Dexamethasone isonicotinate (four puffs bid for seven days, ie, 0.5 mg bid for seven days; last four puffs 30 minutes before TDI) was administered for seven days before the inhalation challenge with TDI (0.010 to 0.015 ppm for 10 to 30 minutes) to each subject, according to a single-blind study design. When the subjects received no treatment, FEV1 markedly decreased and airway responsiveness increased after exposure to TDI. By contrast, when the subjects were treated with dexamethasone-isonicotinate, FEV1 decreased significantly less, but airway responsiveness still significantly increased after exposure to TDI. These results suggest that aerosolized dexamethasone isonicotinate may be used in the prophylaxis of TDI-induced late asthmatic reactions.     

Late asthmatic reactions and changes in histamine responsiveness provoked by occupational agents

The temporal and quantitative relationship between increases in airway responsiveness and late asthmatic reactions provoked by inhalation challenge with occupational agents was studied in nine individuals who underwent a total of thirteen active inhalation challenge tests with one of the following agents: toluene diisocyanate (TDI), maleic anhydride (MA), trimellitic anhydride (TMA), carmine, or colophony (pine wood resin). Airway responsiveness to inhaled histamine (histamine PC20) was measured before and at approximately 3 and 24 h after control and active challenge exposure, when, on all but four occasions, FEV1 was within 10% of pre-challenge values. Significant increases (p less than 0.02) in histamine responsiveness were present at 3 h following challenge exposures which subsequently provoked a definite late asthmatic reaction (FEV1 decrease greater than 15% 3-11 h post challenge). These increases in histamine responsiveness were significantly greater than those at 3 h following the challenges which provoked an isolated early (FEV1 decrease less than 6% 3-11 h post-challenge) or equivocal late asthmatic reaction (FEV1 decrease 6-15% 3-11 h post-challenge) (p less than 0.03). Although histamine responsiveness remained high at 24 h after challenges provoking late asthmatic reactions (p less than 0.05), this was less than the increase at 3 h and not significantly different from the PC20 at 24 h after challenges provoking either single early or equivocal late asthmatic reactions.(ABSTRACT TRUNCATED AT 250 WORDS)     

Inhalation challenge and pharmacologic studies of toluene diisocyanate (TDI)-sensitive workers.

Workers with "sensitivity" to toluene diisocyanate (TDI) studied in depth in an attempt to determine mechanisms of bronchial hyperreactivity. Tests included provocative inhalation challenge (PIC) with TDI and methacholine challenge. Blood samples obtained prior to and at various times after PIC were used to measure complement and split products of complement and plasma histamine levels and to determine dose-response slopes of lymphocyte cyclic adenosine monophosphate (cAMP) following stimulation with agonists. TDI-reactive individuals were all reactive to methacholine and responded to PIC with TDI by immediate, delayed, or dual bronchospastic reactions. No change in plasma histamine, total complement levels, or split products of complement were measurable. TDI reactors gave decreased lymphocyte cAMP dose response slopes to stimulation with isoproterenol, prostaglandin E1, and TDI, which suggests that impairment of adrenergic receptors may play an important role in TDI reactivity.     

Prednisone, indomethacin and airway responsiveness in toluene diisocyanate sensitized subjects

We investigated whether late asthmatic reactions and the associated increase in airway responsiveness induced by toluene diisocyanate (TDI) in sensitized subjects are inhibited by indomethacin and/or prednisone. Four sets of experiments were conducted in five subjects sensitized to TDI. To assess late asthmatic reactions to TDI, FEV1 was measured immediately before and after exposure to TDI and then hourly for 8 h. To assess change in airway responsiveness, the provocative dose (mg) of methacholine that caused a decrease in FEV1 of 20% (PD20FEV1) before treatment, and then before and after exposure to TDI was measured. In the first set of experiments, each subject was given no treatment and was studied before and 8 h after exposure to TDI; in the other two sets, each subject was studied before treatment, then during treatment with indomethacin (50 mg q.i.d. for 3 days, orally) or prednisone (50 mg once a day, for 3 days, orally), both before and 8 h after TDI exposure. In a fourth series of experiments, each subject was again given no treatment and studied before and 8 h after TDI. When the subjects were given no treatment or indomethacin, TDI caused late asthmatic reactions and increased airway responsiveness to inhaled methacholine. In contrast, when the subjects were given prednisone, TDI caused neither late asthmatic reactions nor increased airway responsiveness. Treatment with indomethacin and prednisone did not change baseline FEV1 and airway responsiveness. These results suggest that release of prostaglandins does not contribute to late asthmatic reactions and the associated increase in airway responsiveness induced by TDI. Inflammatory mediators inhibited by prednisone but not by indomethacin may be involved.     

Neutrophil chemotactic activity in toluene diisocyanate (TDI)-induced asthma

We quantitated serum neutrophil chemotactic activity (NCA), which is associated with mast cell or basophil activation, to determine if mast cell or basophil mediators are released during bronchoprovocation-inhalation challenge with subirritant levels of toluene diisocyanate (TDI). Four subjects with suspected TDI-induced asthma and four mite-sensitive subjects with asthma who served as a comparison group were studied. NCA was measured in a multiwell, microchemotaxis chamber. Blood samples were collected, and FEV1 measurements were performed before challenge and at regular intervals during the subsequent 24 hours. Three of four workers clinically sensitive to TDI reacted to a subirritant TDI exposure. There was no increase in NCA during placebo challenges. NCA increased in the three TDI-sensitive workers during early and late asthmatic reactions in quantities proportional to the FEV1 decline. No increase in NCA was found during TDI exposures in the TDI-negative worker. Gel filtration analysis demonstrated the main NCA fraction eluted with macromolecules of an estimated molecular weight greater than 440,000 daltons. This characteristic is compatible with neutrophil chemotactic factor of basophil or mast cell origin. The kinetics of NCA release were similar in mite- and TDI-induced asthmatic reactions. A high correlation (r = 0.97; p = 0.0006) was obtained between the percent decrease in FEV1 during early asthmatic reactions and percent increase in NCA. These observations support the hypothesis that activation of mast cells or basophils is associated with TDI-induced early and late asthmatic reaction.     

Time course of the increase in airway responsiveness associated with late asthmatic reactions to toluene diisocyanate in sensitized subjects

To understand better the mechanism of the increase in airway responsiveness associated with late asthmatic reactions, we determined the time course of toluene diisocyanate (TDI) effect on airway responsiveness in six sensitized subjects who exhibited a late asthmatic response after TDI exposure (0.018 +/- 0.005 ppm, 30 min) in the laboratory. Airway responsiveness was assessed before TDI exposure and then at 8 hr, 1 day, 1 wk, and 1 mo after TDI exposure. To assess responsiveness we determined the provocative dose of methacholine causing a decrease in FEV1 of 20% (PD20FEV1). The methacholine PD20 decreased from 0.50 mg geometric standard error of the mean (GSEM = 1.54) to 0.06 mg (GSEM = 1.55) (p less than 0.001) at 8 hr after exposure to TDI, was still decreased to 0.15 mg (GSEM = 1.93) (p less than 0.05) at 1 day, returned to 0.26 mg (GSEM = 1.91) (p greater than 0.05) at 1 wk, and returned to 0.43 mg (GSEM = 1.71) at 1 mo, indicating that full recovery occurred within 1 to 4 wk. These results demonstrate that TDI-induced late asthmatic response is associated with a reversible increase in airway responsiveness to methacholine and suggest that the TDI effect is linked to an acute inflammatory response in the airways.     

Ketotifen does not inhibit asthmatic reactions induced by toluene di-isocyanate in sensitized subjects

In order to determine whether treatment with ketotifen inhibits asthmatic reactions induced by toluene di-isocyanate (TDI), we studied six sensitized subjects with previously demonstrated dual or late asthmatic reaction after inhalation challenge with TDI. Ketotifen (1 mg b.i.d., orally) or placebo was administered for 7 days to the examined subjects, according to a double-blind, cross-over, placebo-controlled study design. When the subjects were treated with either ketotifen or placebo, FEV1 markedly decreased after exposure to TDI. These results suggest that the anti-asthmatic agent ketotifen is not effective in TDI-induced asthma and suggest that it should not be used in the prophylaxis of asthmatic reactions induced by TDI in sensitized subjects.     

The effect of inhaled allergen on circulating basophils in atopic asthma.

There is increasing evidence for the role of basophils in the allergen-induced late asthmatic response (LAR). To study the effect of inhaled allergen on basophil function in subjects with asthma, ex vivo basophil spontaneous histamine release (SHR) in peripheral blood and plasma histamine was measured before and 2, 5, 10, and 15 minutes, and 2, 4, 6, and 8 hours after allergen bronchial challenge (allergen study day) in six subjects with atopic asthma. Allergen inhalation induced an early response and LAR consisting of a mean (+/- SD) 32.5% (+/- 7.9%) and 28.8% (+/- 7.7%) fall in FEV1, respectively. As a control for the effects of bronchoconstriction, on another occasion, methacholine challenge was performed to produce a mean 33.4% (+/- 3.4%) fall in FEV1 during the early response and no LAR, and blood was obtained to measure basophil histamine release (HR) and plasma histamine. There was a small, but significant (p less than 0.05), rise in median SHR from 4.6% to 6.1% of total basophil histamine after allergen but not after methacholine inhalation. HR remained high after allergen inhalation during the 8 hours of study, whereas it demonstrated a steady, significant, decrease between 4 to 8 hours after methacholine inhalation. No significant changes in plasma histamine were recorded on either allergen or methacholine study days. On a third occasion, SHR was measured after challenge with physiologic saline to control for any effects of methacholine on SHR, and a decrease in HR was recorded during the day similar to HR observed after methacholine challenge. These studies suggest an enhancing effect of inhaled allergen on SHR.(ABSTRACT TRUNCATED AT 250 WORDS)     

Sputum eosinophilia after asthmatic responses induced by isocyanates in sensitized subjects

To assess the nature and the time–course of the cellular component of airway inflammation induced by isocyanates, we examined nine subjects with occupational asthma induced by toluene– or methylene diphenyl–diisocyanate (TDI, MDI) and four control subjects never exposed to isocyanates. Sputum was induced by inhalation of ultrasonically nebulized hypertonic saline (3–4% NaCl) before and 8, 24, 48 h after inhalation challenge with TDI or MDI. Expectorated samples were incubated with dithiothreitol, washed and cytocentrifuged. Differential cell counts were obtained on slides stained with May–Grünwald–Giemsa. Metachromatic cells (mast cells and basophils) were counted on slides stained with toluidine blue at pH 0.1. One occupational asthmatic exhibited a dual reaction to TDI, two exhibited a single early asthmatic reaction to M DI, six exhibited a late asthmatic reaction to TDI (n= 5) or M DI (n= 1), whereas no reactions were observed in control subjects after TDI challenge. In sensitized subjects eosinophils increased from a median value (interquartile range) of 5 (15)% before challenge to 29 (29)% (P= 0.014) and to 30 (31)% (P= 0.031) 8 and 24 h after TDI/MDI challenges, respectively. Sputum eosinophilia was observed both in early and late reactors and declined to near to baseline values 48 hr after challenge. Percentages of eosinophils in control subjects did not exceed 7% during the study. There was a significant correlation between the increase in eosinophil counts and the magnitude of the bronchoconstriction expressed as the area of FEV₁ response to isocyanate challenge (rank correlation coefficient = 0–71, P= 0.014). No significant changes in sputum neutrophils, macrophages, lymphocytes and mast cells were detected. The results indicate that isocyanate–induced asthmatic responses are associated with influx of eosinophils in airway secretion lasting up to 24 h.     

Comparison of plasma histamine and cyclic nucleotides after antigen and methacholine inhalation in man

Serial determinations of plasma histamine and cyclic nucleotides (adenosine monophosphate [AMP] and guanosine monophosphate [GMP]) were performed after inhalation of antigen and methacholine in four groups of subjects. In the first group, consisting of six antigen-sensitive subjects exhibiting bronchospasm after inhalation of ragweed or grass antigen, plasma histamine was elevated within 2 min and persisted for 30 min after inhalation of antigen. Peak histamine levels were between 18 to 80 ng/ml. In the second group, consisting of four nonatopic subjects, neither bronchospasm nor histamine was observed, despite inhalation of the same or 10-fold increased concentrations of antigen. In the third group, consisting of six subjects (three atopic and three nonatopic) exhibiting bronchospasm after inhalation of 2.5 to 10 mg of methacholine, sustained increases of histamine began at 1 min and persisted for 60 min after inhalation of methacholine. In the fourth group, seven subjects (two atopic, five nonatopic) without demonstrable bronchospasm despite inhalation of 2.5- to 10-fold increased doses of methacholine, no histamine was detected in the plasma at any time after inhalation of methacholine. Serial measurements of cyclic nucleotides showed no consistent changes in serum levels of cyclic AMP or cyclic GMP following inhalation challenge. We conclude that serum levels of histamine but not cyclic nucleotides change during bronchospasm induced by either antigen or methacholine.     

Venous blood platelets decrease during allergen-induced asthmatic reactions

To determine whether circulating platelets alter during asthmatic reactions induced by allergens, we studied nine subjects previously shown to develop an early or dual asthmatic reaction after inhalation challenge with extracts of house dust mite or grass pollen. In each subject, FEV1, circulating platelets and leucocytes were measured before, 15, 30 and 60 min, and 2, 4, 6 and 8 hr after inhalation of allergen and diluent control administered in a single-blind, randomized fashion. The same procedure was repeated in six of the nine subjects after bronchoconstriction induced by methacholine. Each subject developed an early asthmatic reaction after allergen inhalation challenge, which was followed by a late asthmatic reaction in six subjects and by an equivocal late asthmatic reaction in two of them (fall in FEV1 of 15 and 17% respectively). Compared with the control day, circulating platelets significantly decreased during the allergen-induced early asthmatic reaction (P less than 0.025, at 30 min). Platelet counts returned to baseline values within 4 hr and remained steady thereafter both in subjects who did and did not develop a late asthmatic reaction. No changes in platelet counts occurred after bronchoconstriction induced by methacholine. Diurnal increase of leucocyte numbers occurred after challenge with both allergen and diluent control. These results suggest that platelets may be involved in the pathogenesis of allergen-induced asthmatic reactions.     

Significant changes in nonspecific bronchial responsiveness after isolated immediate bronchospecific reactions caused by isocyanates but not after a late reaction caused by plicatic acid

Although late bronchospastic reactions after exposure to antigenic and sensitizing agents usually significantly alter bronchial responsiveness to histamine or methacholine, presumably by causing bronchial inflammation, isolated immediate bronchospastic reactions do not induce such changes. We studied three subjects who demonstrated different patterns of reaction. The first individual was diagnosed as having occupational asthma to red cedar. This was confirmed by specific inhalation challenges that resulted in late bronchospastic reaction. No significant changes in the provocative concentration of histamine causing a 20% fall in FEV1 (PC20) were found 1 day after this reaction. Two weeks later, serial assessments (five and six, respectively) of PC20 histamine were recorded on control days and up to 48 hours after exposure to plicatic acid, which caused a late bronchospastic reaction with a maximum fall of 37% in FEV1. No significant changes in PC20 were found; the maximum variations on control days were 0.36 to 0.74 mg/ml, and on active days, from 0.37 to 0.59 mg/ml. By contrast, two other subjects, who demonstrated isolated immediate reactions after exposure to diphenylmethane diisocyanate, had significant changes in PC20 histamine and methacholine, in one subject from 3.1 mg/ml to 0.6 mg/ml 8 hours after exposure, and in the other subject, from 61.0 to 7.4 mg/ml 7 hours after exposure, with recovery during the next few days. These examples demonstrate that the pattern of nonspecific bronchial responsiveness after immediate and late bronchospastic reactions can be different from what has previously been described. Immediate bronchospastic reactions may lead to bronchial hyperresponsiveness, whereas late asthmatic reactions do not always induce changes in bronchial responsiveness.(ABSTRACT TRUNCATED AT 250 WORDS)     

Late bronchial response and increase in methacholine hyperresponsiveness after exercise and distilled water challenge in atopic subjects with asthma with dual asthmatic response to allergen inhalation

We investigated the occurrence of late asthmatic response and increased methacholine responsiveness after exercise and ultrasonically nebulized distilled water (UNDW) inhalation in 12 subjects with asthma with dual asthmatic response and increased responsiveness after allergen challenge. On 3 separate days, allergen, exercise, and UNDW challenges were performed 2 hours after methacholine. FEV1 was measured for 8 hours to detect any delayed change in airway caliber. If there were a further significant reduction in FEV1 after the recovery from the immediate bronchoconstriction, methacholine challenge was performed again when FEV1 had returned to baseline. Reproducibility of any observed late response to exercise and UNDW was also investigated by repeating these challenges on 2 subsequent days. After allergen inhalation only nine subjects had an early asthmatic response, whereas all the tested subjects demonstrated a late reaction and increased methacholine responsiveness. Ten subjects had an immediate response to exercise, and this was followed by a late response in only four patients. Nine subjects demonstrated early response to UNDW inhalation, and five subjects also had a late reaction. These late responses were associated with an increase in methacholine responsiveness in a subset of the tested subjects. Late-phase reactions to exercise and UNDW were not reproducible.     

Clinical and immunological evaluation of isocyanate-exposed workers.

Isocyanates are the most significant cause of occupational asthma in our country. To evaluate the prevalence of work-related respiratory symptoms and immunologic sensitization to it, we performed a questionnaire survey, allergy skin test, radioallergosorbent test (RAST) to toluene diisocyanate (TDI)-human serum albumin (HSA) conjugate and methacholine bronchial challenge test on 23 isocyanate-exposed employees and 9 unexposed controls working in a zipper factory. Six employees (26.1%) complained of work-related respiratory symptoms and three symptomatic workers showed significant bronchoconstrictions on TDI-bronchoprovocation test. Three (13%) asymptomatic workers had high specific IgE antibodies to TDI-HSA and none of the TDI-sensitive asthmatic workers had specific IgE antibody. One of the TDI-sensitive asthmatic workers showed a negative result on the initial methacholine bronchial challenge test, but bronchial hyperresponsiveness developed after the TDI challenge. It was suggested that TDI-sensitive asthma was noted in three (13%) of 23 exposed workers and that asymptomatic workers could have high specific IgE antibody. Measurement of the changes in bronchial hyperresponsiveness after the TDI challenge could be helpful to diagnose TDI-sensitive asthma.     

Eosinophil granule proteins in serum after allergen challenge of asthmatic patients and the effects of anti-asthmatic medication

Thirteen allergic asthmatic patients were challenged six times each and serum levels of ECP (eosinophil cationic protein), EPX (eosinophil protein-x) and blood counts of eosinophil granulocytes were measured in blood obtained before and at regular intervals after challenge. Three challenges were performed in a blinded and randomized fashion and included a one-dose pretreatment with the inhalant anti-asthmatic drugs disodium cromoglycate, terbutaline and budesonide. One challenge was performed after 4 weeks' pretreatment with the inhalant budesonide and one was a histamine challenge. Pre-challenge levels of ECP were significantly reduced both after 4 weeks and after a one-dose treatment with budesonide whereas the EPX levels were reduced only after the former. Blood eosinophil counts were unaffected by the challenge whereas the ECP levels were significantly reduced after the placebo challenge and when premedicated with disodium cromoglycate and terbutaline. The EPX levels stayed unaltered at the placebo challenge but were significantly reduced when the patients were premedicated with terbutaline. ECP and EPX levels as well as blood eosinophil counts before challenge were significantly related to the development of the late asthmatic reaction. The results again focus on a relation between the eosinophil granulocyte and asthma and suggest that an increased activity of the blood eosinophil, as suggested by the raised serum levels of the granule proteins ECP and EPX, is one prerequisite for the development of chronic asthma.     

Immunological investigation of individuals with toluene diisocyanate asthma

Thirteen subjects who experienced only the expected irritant respiratory and ocular effects from occupational exposure to toluene diisocyanate (TDI) were compared with eight workers who appeared clinically to be sensitized to this substance, as manifested by the prompt development of asthmatic symptoms on exposure to minute concentrations of TDI. In an attempt to document an immunological response to TDI in the latter group, several conjugates of TDI with human serum albumin were prepared. Gel diffusion, leucocyte histamine release, PCA in guinea-pigs, passive haemagglutination, passive transfer (P-K) and a few direct skin tests all failed to show antibodies to TDI. In lymphocyte culture, however, TDI–human serum albumin complexes produced stimulation of lymphocytes from seven of the eight subjects suspected of being sensitized and none of the controls.     

Blood markers of early and late airway responses to allergen in asthmatic subjects. Relationship with functional findings

We evaluated the relationship between blood markers of mast-cell (plasma histamine and serum level of heat-stable neutrophil chemotactic activity [NCA]) and eosinophil (serum eosinophil cationic protein [ECP]) activation during early airway response (EAR) and late airway response (LAR) to allergen inhalation in 24 asthmatic subjects. After EAR, 14 subjects showed significant LAR (FEV₁ fall: 25%), while 10 subjects showed equivocal LAR (FEV₁ fall: 15–20%). A significant increase from baseline value was observed in plasma histamine and in serum NCA during both EAR and LAR, while serum ECP significantly increased only during LAR. The sensitivity of different markers to detect significant FEV₁ fall during EAR and LAR was low, except for NCA. Changes in blood mediators were similar in both groups with significant and equivocal LAR. There was a significant relationship between the increase in NCA during EAR and the severity of LAR. Stepwise regression between changes in different blood markers showed a significant relationship between histamine increase during EAR and ECP increase during LAR. Thus, serum NCA is a more sensitive marker of EAR and LAR than plasma histamine and serum ECP, and its increase during EAR seems predictive of the severity of the subsequent LAR.     

Importance of inflammatory and immune components in a mouse model of airway reactivity to toluene diisocyanate (TDI)

BACKGROUND: Nearly 9 million individuals are exposed to agents in the workplace associated with asthma, and isocyanates represent the most common cause of occupationally induced asthma. OBJECTIVES: Nonetheless, the immunological mechanisms responsible for isocyanate-induced asthma are not clear. A murine model for toluene diisocyanate (TDI) asthma is described and employed to examine inflammatory and immune components that may be involved in the disease. METHODS: Groups (n = 6) of C57BL/6J and athymic mice were sensitized by subcutaneous injection (20 microl on day 1, 5 microl on days 4 and 11), and 7 days later challenged by inhalation (100 p.p.b., days 20, 22 and 24) with TDI. Twenty-four hours following the last challenge the tracheae and lungs were examined for histological changes as well as for the expression of Th1, Th2 and pro-inflammatory cytokines. Mice were also examined for airway reactivity to methacholine challenge and for specific and total IgE and IgG antibodies. RESULTS: TDI sensitization resulted in increased reactivity to methacholine challenge as well as a significant inflammatory response in the trachea and nares of wild-type mice, but not in the athymic mice nor in the lungs of the C57BL/6J mice. Airway inflammation was characterized by inflammatory cell influx, goblet cell metaplasia and epithelial damage. Histological changes in the trachea were accompanied by increased mRNA expression of interleukin (IL)-4, tumour necrosis factor alpha, lymphotoxin beta, lymphotactin and Rantes, as well as TDI-specific IgG antibodies and elevated levels of total IgE. IgE-specific antibodies were not detected with this exposure regimen but were produced when the TDI concentrations were increased. CONCLUSIONS: These studies provide a unique murine model for occupational asthma that generates both inflammatory and immune mediators similar to those occurring in TDI-induced asthma in humans.     

Follow-up study of patients with respiratory disease due to toluene diisocyanate (TDI)

The outcome of the respiratory symptoms, pulmonary function tests and bronchial hyperresponsiveness was studied in forty-seven workers with respiratory disease due to toluene diisocyanate (TDI) (twenty-seven asthmatic and twenty non-asthmatic subjects) after about 2 years from the first examination. Eight of twelve asthmatic subjects who left the industry after the first examination complained at the follow-up of dyspnoea and wheezing, but pulmonary function tests were unchanged; bronchial hyperresponsiveness decreased in three, but most were still positive to challenge test with bethanechol at the follow-up. Fifteen subjects who continued their exposure to TDI showed at the follow-up a significant decrease of the spirometric parameters and an increase of the bronchial hyperresponsiveness, and symptoms of chronic bronchitis were more frequent at the second examination. Non-asthmatic subjects, both exposed and non-exposed to TDI at the second examination, showed a significant decrease of the pulmonary function tests but no relevant changes in bronchial hyperresponsiveness. Our data suggest that stopping occupational exposure to TDI frequently did not produce an improvement of the TDI bronchial asthma, and persistence of the occupational exposure causes a more rapid decline in the respiratory function.