Richard J. Martin

The role of inflammation in the pathogenesis of severe asthma chronically treated with high doses of glucocorticoids is poorly understood. Despite this, treatment has been aimed at advancing anti-inflammatory and immunomodulator therapy. This study was designed to evaluate both the presence and type of airway inflammation in patients with severe asthma. A prospective bronchoscopic study evaluated 14 severe, high-dose oral glucocorticoid dependent asthmatics. Bronchoalveolar lavage fluid was analyzed for cytology and inflammatory mediators. Endobronchial and transbronchial biopsies were performed in selected patients for morphometric evaluation of macrophage/monocytes, neutrophils, eosinophils and lymphocytes. These results were compared with lavage and endo- and transbronchial biopsy studies in normal controls and patients with moderate asthma. The concentration of eosinophils in bronchoalveolar lavage fluid was highest in the moderate asthmatics not on glucocorticoids, with very little difference between normal controls and severe asthmatics (significant difference among the groups, p = 0.007). In contrast, the severe asthmatics demonstrated a twofold higher concentration of neutrophils in lavage than either the mild-moderate asthmatics, or the normal controls (p = 0.032 among the groups, p < 0.05 between the severe asthmatics and both controls). Similar results were obtained in the endobronchial and transbronchial biopsy specimens, which consistently showed significantly higher numbers of neutrophils in the severe asthmatics than in the control groups. The eicosanoid mediators, thromboxane and leukotriene B4, were also highest in the severe asthma group (differences among the groups, p = 0.019 and p = 0.023, respectively). These findings suggest that inflammation remains in severe symptomatic asthmatics despite treatment with high dose glucocorticoids which may be due to the severity of disease, glucocorticoid treatment, or other as yet undefined factors.

The histopathology of bronchial asthma is associated with structural changes within the airways, including subepithelial fibrosis, as well as chronic eosinophilic inflammation. The mechanisms responsible for this tissue remodeling, and in particular the role of inflammatory cells, remain to be established. Transforming growth factor-beta (TGF-beta) is a potent profibrotic cytokine which may contribute to the thickening of the reticular lamina by the deposition of collagen fibers. To investigate the molecular mechanisms underlying these structural changes, we have investigated the expression of TGF-beta1 mRNA and immunoreactivity within the bronchial mucosa of mild to severe asthmatic individuals and normal control subjects using the techniques of in situ hybridization and immunocytochemistry. As eosinophils are prominent within the asthmatic airway and are known to synthesize pro-inflammatory cytokines, the presence of TGF-beta1 mRNA and immunoreactive protein in eosinophils was also examined. Asthmatic individuals exhibited a greater expression of TGF-beta1 mRNA and immunoreactivity in the airways submucosa than normal control subjects (P < 0.05), and these increases were directly related to the severity of the disorder. The extent of airways fibrosis, as detected histochemically, was also increased in asthmatics compared with normal control subjects (P < 0.005). In asthmatic subjects, the presence of subepithelial fibrosis was associated with the severity of the disease and correlated with the decline in forced expiratory volume in 1 s (r2 = 0.78; P < 0.05). Within the asthmatic airways, EG2-positive eosinophils represented the major source of TGF-beta1 mRNA and immunoreactivity. These results provide evidence that TGF-beta1 may play a role in the fibrotic changes occurring within asthmatic airways and that activated eosinophils are a major source of this cytokine.

As physiologic and autopsy evidence suggests that peripheral airways and parenchyma are involved in asthma, we hypothesized that significant alveolar tissue inflammation is present in patients with stable, chronic asthma. Eleven patients with nocturnal asthma (NA) and 10 patients with non-nocturnal asthma (NNA) were studied. Each subject underwent two bronchoscopies with proximal airway endobronchial and distal alveolar tissue transbronchial biopsy in a random order at 4:00 P.M. and 4:00 A.M. Morphometric analysis was used to determine the number per volume (Nv) of inflammatory cells. Between-group comparisons showed that the Nv of eosinophils was greater in the NA alveolar tissue 4:00 A.M. compared with the subjects with NNA (40.2 x 10(3) [26.4-57.1 x 10(3), IQ] versus 15.7 x 10(3) [2.1-35.2 x 10(3), IQ], p = 0.05). In regard to the airway biopsies, no difference in the inflammatory and epithelial cells between the two groups was seen at either time. The NA group exhibited greater eosinophils and macrophages in the alveolar tissue at 4:00 A.M. compared with 4:00 P.M. (40.2 x 10(3) [26.4-57.1 x 10(3), IQ] versus 10.3 x 10(3) [2.7-16.8 x 10(3), IQ], p = 0.016 for eosinophils and 215.1 x 10(3) [129.9-356.1 x 10(3), IQ] versus 166.3 x 10(3) [150.7-212.6 x 10(3), IQ], p = 0.031 for macrophages). Only alveolar tissue eosinophils, not proximal airway tissue eosinophils, correlated with the nocturnal decrement in lung function (r = -0.54, p = 0.03). These findings suggest that eosinophils and macrophages accumulate to a greater extent in the alveolar tissue and these changes contribute more to the variation in lung function compared with inflammation in the more proximal tissue.