Letter to the Editor Allergen-specific IgE is not detectable in the bronchial mucosa of nonatopic asthmatic patients To the Editor: Activation by aeroallergen-specific IgE of bronchial mucosal mast cells in clinically sensitized atopic subjects is an acknowledged exacerbating (some speculate causative) stimulus for asthma, although the existence of the disease in nonatopic subjects, who are conventionally defined as those with absence of allergen-specific IgE, as determined by using skin prick and in vitro tests, begs the question of whether allergens and IgE play an indispensable role in asthma pathogenesis. We have previously shown that nonatopic asthmatic patients, like atopic patients, display the entire molecular machinery to support B-cell switching in the bronchial mucosa1 and that this does indeed occur,2,3 with indirect evidence of increased local IgE synthesis.4 Epidemiologically, increased IgE production is a major risk factor for asthma, regardless of atopic status.5 One possible explanation for this paradox is that IgE is manufactured in the bronchial mucosa of nonatopic asthmatic patients but remains confined there and bound to cells bearing its receptors. To address this, we hypothesized that local IgE synthesis in the bronchial mucosa of both atopic and nonatopic asthmatic patients results in greater local total IgE concentrations than in serum and, in the case of nonatopic asthmatic patients, production of allergen-specific IgE that is sequestered in the mucosa and therefore not detectable in the periphery. We determined the concentrations and allergen specificities of IgE in the blood and bronchial mucosa of a group of atopic and nonatopic asthmatic patients and nonatopic control subjects, not only to a panel of allergens conventionally used for skin prick testing in the United Kingdom but also to an extended panel of more than 100 known allergen components. There were 10 subjects in each study group (Table I). All provided written informed consent to participate in the study, which was approved by a local research ethics committee. Ten bronchial mucosal biopsy specimens were collected from the right or left, second- or third-generation bronchi at fiberoptic bronchoscopy. Biopsy specimens were weighed, then snap-frozen and homogenized (see the Methods section in this article’s Online Repository at www.jacionline.org). Serum was collected on the same day. Samples were stored at 2808C until

analysis. Analysis was generally performed on pooled triplicate biopsy extracts; however, all 10 biopsy specimens were analyzed individually in one of the subjects to assess between-specimen variability (see the Methods section in this article’s Online Repository at www.jacionline.org). Total and allergen-specific IgE concentrations in aliquots of serum and mucosal homogenates were measured by using commercial assays (Phadia ImmunoCAP-100 and ImmunoCAP ISAC, respectively; Phadia, Uppsala, Sweden), according to the manufacturer’s instructions (see the Methods section in this article’s Online Repository at www.jacionline.org). By using these techniques, IgE was detectable in the serum and bronchial mucosa of all study subjects (see Fig E1 in this article’s Online Repository at www.jacionline.org). The median total IgE concentrations in mucosal homogenates were significantly increased in both the atopic and nonatopic asthmatic patients compared with those seen in control subjects, even allowing for variability of IgE concentrations between different mucosal sites (Fig 1 and see Fig E2 in this article’s Online Repository at www. jacionline.org). Interestingly, this was not reflected in sera, in which only the median total IgE concentration in atopic asthmatic patients was significantly greater than in control subjects, although with a similar trend in the nonatopic asthmatic patients. By using the ImmunoCAP ISAC microarray, some allergen component–specific IgE species were detectable in sera and mucosal homogenates from the atopic asthmatic patients but not the nonatopic asthmatic patients and control subjects. Where detectable, the relative concentrations of a minority of these species, expressed as percentages of total IgE (see Figs E3-E5 in this article’s Online Repository at www.jacionline.org) or absolute concentrations (see Tables E1-E3 in this article’s Online Repository at www. jacionline.org), were higher in the bronchial mucosa than in the serum, although most were lower. To investigate the possible heterogeneity of distribution of allergen component–specific IgE in the bronchial mucosa, we compared concentrations in 9 geographically separate biopsy specimens from a single atopic asthmatic patient (see Table E4 in this article’s Online Repository at www.jacionline.org). Component-specific IgE was detectable in 4 of the 9 biopsy specimens, typically when the serum concentration of the same species was particularly increased. So far as we are aware, this is the first study in which total and allergen-specific IgE levels have been measured successfully in the bronchial mucosa. The data are consistent with the hypothesis that IgE synthesis, sequestration, or both are ongoing in the bronchial mucosa of both nonatopic and atopic asthmatic patients, but not that this IgE is directed against common, local

TABLE I. Demographics and lung function of study subjects and corticosteroid therapy of asthmatic patients Subject group

Nonatopic control subjects Nonatopic asthmatic patients Atopic asthmatic patients

Age (y)

Sex (F/M)

FEV1 (% predicted)

Inhaled corticosteroid dosage (mg/d BDP equivalent)

23 (21-36) 54 (24-70)* 30.50 (24-66)*

3/7 4/6 4/6

104.5 (94-128) 67.5 (40-101)  95 (64-130)à

1800 (640-4000) 150 (0-1600)§

Age, FEV1 percent predicted, and inhaled corticosteroid dosages are expressed as medians (ranges). Three nonatopic asthmatic patients were taking regular oral prednisolone in addition to inhaled corticosteroids. BDP, Beclomethasone dipropionate; F, female; M, male. _ .01 and  P < _ .005 versus control subjects and àP 5 .02 and §P 5 .002 versus nonatopic asthmatic patients (Mann-Whitney U test). *P
100

8.5

80