Background: IL-4 and IL-13 have been shown to be critical for expression of the asthma phenotype in a murine model and may modulate human fibroblast function.
Objective: We hypothesized that IL-4 and IL-13 would increase airway fibroblast proliferation and reduce the ability of dexamethasone to decrease this proliferation.
Methods: Six subjects with severe asthma, 5 subjects with mild asthma, and 5 healthy subjects underwent bronchoscopy with endobronchial biopsy. Biopsy specimens were placed in Dulbecco modified Eagle medium and cultured, and only fibro-blasts from the first and second passages were evaluated. Cells were incubated with IL-4 (50 ng/mL), IL-13 (10 ng/mL), and the combination for 48 hours in the presence and absence of dexamethasone, 10(-7) mol/L, and 10(-8) mol/L. Fibroblasts were also incubated with IFN-gamma at 50 ng/mL to assess the response of a T(H)1 cytokine on proliferation.
Results: Fibroblast proliferation, determined by (3)H-thymidine incorporation, was significantly increased by IL-4 in subjects with mild asthma as compared with IL-4 in subjects with severe asthma and healthy subjects (P =.003), IL-13 (P =.011), and the combination (P =.004). Dexamethasone also increased proliferation in the group with mild asthma as compared with the group with severe asthma and the healthy group (10(-7) mol/L, P =.02; 10(-8) mol/L, P =.02). IFN-gamma did not significantly alter airway fibroblast proliferation.
Conclusion: IL-4, IL-13, and dexamethasone all significantly increased fibroblast proliferation in subjects with mild asthma.