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  • Title: Increased TGF-beta2 in severe asthma with eosinophilia.
    Author: Balzar S, Chu HW, Silkoff P, Cundall M, Trudeau JB, Strand M, Wenzel S.
    Journal: J Allergy Clin Immunol; 2005 Jan; 115(1):110-7. PubMed ID: 15637555.
    Abstract:
    BACKGROUND: Airway eosinophilia and thickened subepithelial basement membrane have previously been reported to increase with increases in TGF-beta expression. However, little is known regarding the expression of specific TGF-beta isoforms (TGF-beta1, TGF-beta2, and TGF-beta3) in asthma, despite recent evidence suggesting that isoforms may have differing biologic activities. OBJECTIVE: This study examined airway tissue expression of the 3 TGF-beta isoforms and several downstream pathway elements in 48 patients with severe asthma with or without persistent eosinophilia, 14 patients with mild asthma, and 21 normal subjects. METHODS: Immunochemistry/immunofluorescence, quantitative real-time PCR and enzyme immunoassay were used to evaluate the 3 TGF-beta isoforms, their receptors, collagen I deposition, connective tissue growth factor expression, and tissue inhibitor of metalloproteinases 1 levels. RESULTS: Of the isoforms, only TGF-beta2 was different among the groups and increased in severe asthma (overall P < .0001). The increase was due to severe asthma tissue eosinophils which, unlike eosinophils in other groups, expressed high amounts of TGF-beta2. Subjects with severe asthma also had the thickest subbasement membrane and highest tissue inhibitor of metalloproteinases 1 levels. In contrast, TGF-beta receptor 1 and connective tissue growth factor were both consistently downregulated in asthma, regardless of severity. CONCLUSION: TGF-beta2, expressed mainly by eosinophils, is the predominant isoform expressed in severe asthma, and is associated with increased profibrotic responses. Decreased expression of TGF-beta receptor 1 and connective tissue growth factor in all asthma severity groups suggests a degree of activation of the TGF-beta pathway in airway tissue of all asthmatic compared with normal airways.
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