Increases in collagen type I synthesis in asthma: the role of eosinophils and transforming growth factor-beta

Clin Exp Allergy. 2002 Jun;32(6):860-5. doi: 10.1046/j.1365-2745.2002.01404.x.


Background: Collagen type I is one of the major deposits in thickening of the reticular basement membrane of asthma.

Objective and methods: In this study, we assessed turnover of collagen type I in asthma by measuring procollagen type I C-terminal peptide (PICP) and collagen type I C-terminal telopeptide (ICTP) in induced sputum.

Results: PICP but not ICTP was found to be significantly higher in asthma subjects than in normal volunteers (P < 0.05). In asthma, PICP was inversely correlated with %FEV(1.0) (r = -0.539), and its levels significantly increased upon exacerbation (P < 0.05), indicating that collagen synthesis increases during asthma exacerbation. Additionally, PICP was found to significantly correlate with eosinophil counts in sputum (r = 0.539), indicating that eosinophils stimulate collagen turnover. Because eosinophils can produce TGF-beta, a potent stimulator of collagen synthesis, we immunocytochemically examined TGF-beta-positive cells in sputum. TGF-beta-positive cells significantly correlated with eosinophil counts (r = 0.811) and PICP (r = 0.569), suggesting that TGF-beta released from eosinophils is involved in collagen synthesis.

Conclusions: The results of the present study suggest that collagen synthesis is stimulated in asthmatic airways by eosinophils through TGF-beta, while collagen degradation is not, and that PICP in sputum can act as a new marker for airway inflammation in asthma.

Publication types

  • Comparative Study

MeSH terms

  • Asthma / metabolism*
  • Asthma / physiopathology
  • Biomarkers / blood
  • Collagen Type I / biosynthesis*
  • Enzyme-Linked Immunosorbent Assay
  • Eosinophils / physiology
  • Female
  • Forced Expiratory Volume / physiology
  • Humans
  • Immunochemistry
  • Leukocyte Count
  • Male
  • Middle Aged
  • Peptide Fragments / biosynthesis*
  • Peptide Fragments / metabolism*
  • Peptides
  • Procollagen / biosynthesis*
  • Procollagen / metabolism*
  • Serum Albumin / metabolism
  • Sputum / chemistry
  • Sputum / metabolism
  • Statistics as Topic
  • Transforming Growth Factor beta / physiology


  • Biomarkers
  • Collagen Type I
  • Peptide Fragments
  • Peptides
  • Procollagen
  • Serum Albumin
  • Transforming Growth Factor beta
  • collagen type I trimeric cross-linked peptide
  • procollagen type I carboxy terminal peptide