Five of the six previously reported studies in which an association between coeliac disease and DR7 was found were from paediatric centres. Of the two studies recording an association with DR3 alone, one concerned adults only9; a second study included a mixed group of children and adults, though 74%O were adults7 (table III). The association of coeliac disease with DR3 and DR7 may be interpreted on the basis of more than one model. The condition may, for example, be genetically homogenous and dependent on a susceptibility gene at a locus linked to the DR locus and in linkage disequilibrium with both DR3 and DR7. In this regard it is relevant that the DC3 specificity at the DC locus is in linkage disequilibrium with DR3 and DR7, and Tosi et al put forward evidence to suggest that the primary association was with DC3.'2 A recent study of patients with coeliac disease who were DR3 and DR7 negative, however, failed to confirm this.'3 Our finding of heterogeneity of the DR association argues against this simple model and suggests the possibility of more than one susceptibility gene-namely, DR3 and DR7 or genes in linkage disequilibrium, one with DR3 and one with DR7. If the presence of both genes promotes an early onset of disease, and the presence of only DR3 or a gene in linkage disequilibrium with DR3 a later onset, the present findings would be explained. Further studies of the association of coeliac disease with DR and t)C antigens are being carried out, and it seems important that age of onset of disease should be taken into account. Other than the age of onset, HLA differences do not seem to have any influence on other clinical variables. Kumar et al found that HLA factors did not appear to make any difference to the mode of presentation.'4 References 1 Ek J, Albrechsten D, Solheim BG, Thorsby E. Strong association between HLA-DW3 related B-cell alloantigen-DRW3 and coeliac disease. Scand J

Exposure and sensitization to dog allergen is a significant cause of asthma. In this study we investigated the distribution, aerodynamic characteristics, and particle-size distribution of the major dog allergen Can f 1. Dust samples were collected in 50 homes with a dog and 50 homes without dogs. Airborne Can f 1 concentration was measured in 28 homes with dogs and 36 homes without a dog. Particle-size distribution was determined by using 10 separate Andersen sampler measurements in a dog-handling facility, and in 10 homes with dogs, and by repeated measurements in a home with one dog. High levels of Can f 1 (> 10 microg/g) were found in dust in all but one home with a dog and in eight of 50 homes without dogs. Airborne Can f 1 levels varied greatly between the homes with dogs (range: 0.3 to 99 ng/m3). Low levels of airborne Can f 1 (range: 0.4 to 1.1 ng/m3) were detected in 11 of 36 homes without a dog. Can f 1 was predominantly associated with large particles collected on the first stage of the Andersen sampler (> 9 microm), which averaged 42 to 49% of the total allergen recovered in the dog-handling facility and in homes with dogs. Small particles (< 5 microm diameter) also carried Can f 1, and these particles comprised approximately 20% of the total airborne allergen load. There was an excellent concordance between the results obtained in different sampling areas, and between the total Can f 1 recovered on the Andersen sampler and on the parallel filter. In conclusion, airborne Can f 1 was detectable in undisturbed conditions in all homes with dogs and in almost one third of the homes without dogs. In houses with dogs, a significant proportion (approximately 20%) of airborne Can f 1 was associated with small particles (< 5 microm diameter). Owing to their aerodynamic characteristics, these particles would be expected to remain airborne for a long period and, when inhaled, could penetrate into the lower airways and initiate asthma attacks.

No single antibody is able to differentiate reliably between these two tumours. The use of a small panel of antibodies with a high combined sensitivity and specificity is recommended.

Upholstered seats from public places constitute a reservoir for the accumulation of dog allergen, and a source of exposure to Can f 1 inside public buildings or on public transport. Exposure to cockroach allergens in schools may be important for cockroach sensitized asthmatic children.

Low levels of mite allergen are unlikely to be of any clinical significance to mite-sensitive asthmatic patients. However, upholstered chairs in hospitals constitute a significant reservoir of cat and dog allergen. Inhalation of airborne allergen in patients attending their hospital appointment may exacerbate asthma in those highly allergic to cats or dogs. These results question the wisdom of introducing soft furnishings and carpets into hospitals. Three-times weekly vacuuming significantly reduces allergen levels in upholstered chairs.

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Objectives-The aims of this study were to document the prevalence of work related upper and lower respiratory tract symptoms in workers exposed to organic dusts and to identify variables predictive of their occurrence. Methods-A cross sectional survey with an administered questionnaire (a previously validated adaptation of the Medical Research Council (MRC) respiratory questionnaire) was performed. Symptoms were classified as work related by their periodicity. Demographic data, smoking habits, and occupational histories were recorded. Personal exposures to dust and endotoxin were measured and individual subjects ascribed an exposure value specific to occupation, site and industry. Cox's regression techniques were used to identify variables predictive of work related upper and lower respiratory tract symptoms. Information was stored using Dbase 3 and analysed with SPSS. Results-1032 Workers (93 % of the target population) were studied in nine diVerent industries. The highest prevalences of work related lower respiratory tract symptoms (38.1 %), upper respiratory tract symptoms (45.2 %), and chronic bronchitis (15.5 %) were found among poultry handlers. White workers were significantly more likely to complain of upper and lower respiratory tract symptoms. An individual in the swine confinement industry had a symptom complex compatible with byssinosis. Increasing current personal exposures to dust or endotoxin were found to be predictive of upper and lower respiratory tract symptoms, chronic bronchitis, and byssinosis. In a univariate analysis a relation between current exposures and the organic dust toxic syndrome was found. Present smoking and previously documented respiratory tract illness were significantly predictive of work related lower respiratory tract symptoms. Women were more likely to report work related upper respiratory tract symptoms. Conclusions-People exposed to organic dusts may have a high prevalence of work related respiratory tract symptoms which are related to dust exposures and smoking habits. Action should be taken to reduce exposures to dust and endotoxin and stopping smoking should be promoted among workers exposed to organic dusts to reduce morbidity. (Occup Environ Med 1998;55:668-672)

Immunohistochemistry is of limited value, but newer diagnostic methods may be useful additions in this area of pathology. The diagnostic importance of histological features seen on plain tissue sections is emphasized as vital for correctly differentiating between benign pleural disease and malignant pleural mesothelioma.