SummaryA clinical, pathological and immunological study was made of fifty cases of asthma developing in adult life—twenty‐seven females and twenty‐three males. The mean age of appearance of asthma was 51 years. In spite of the paroxysmal onset observed in thirty‐nine cases, the course was always severe, leading to dependence upon corticosteroid treatment in thirty‐six cases. Two‐thirds of the subjects had either a personal or familial atopic history, one‐third had positive skin tests to routine respiratory allergens, and one‐third had a peripheral blood eosinophilia higher than 400 mm3. Total serum IgE was not raised in any case and attempts at hyposensitization were not effective. The titre of serum complement was normal and investigation for autoantibodies was negative in thirty‐one subjects. Study of the HLA system in twenty‐eight cases showed a significantly raised frequency of antigen HLA9. The bronchial biopsies were examined histologically in thirty‐one cases and by fluorescence examination in fifteen. The histological appearance was sterotyped and non‐specific. There was some modification of the lining consisting of thickening and irregularity of the basal membrane with evidence of hyperfunction of adjacent mesenchymal tissues. The basal membrane showed thickening, estimated in two cases by electron microscopy to be of 20–30 μm. This was due largely to collagen, which concealed the true basal membrane, the ultrastructure of which was well preserved.Immunofluorescence tests made it possible to show the presence of IgA, IgG and IgM constantly associated with the C3 component of complement. This was localized mainly in the superficial part of the thickened basal membrane and in the cytoplasm of the epithelioid cells. Fibrin showed a different appearance, with irregular fluorescence situated essentially along the base of the superficial epithelial membrane. These immunofluorescence findings are compatible with transudation and also of a lo
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