Background In bronchial mucosa, T cells are in close association with fibroblasts. This cell contact raises the possibility of cross-talk between the two cell types through cytokines, such as interleukin-4 (IL-4).
Objective We postulated that IL-4 may modulate collagen synthesis and degradation in the fibroblasts of asthmatics.
Methods Bronchial fibroblasts from asthmatics (BAF) and normal controls (BNF) were stimulated with IL-4. Procollagen I gene expression and protein production were measured by real-time PCR, RT-PCR, and radioimmunoassay. The effect of IL-4 on the regulation of procollagen I (α1) promoter was studied through transient cell transfections. The implication of Sp1 and AP-1 in regulating IL-4-induced procollagen I (α1) production was determined. The effect of IL-4 on metalloproteinase-2 (MMP-2) and tissue inhibitor of metalloproteinase-2 (TIMP-2) production and gene expression was evaluated.
Results Following IL-4 stimulation, there was a significant increase in the expression of mRNA of procollagen I (α1) by human bronchial fibroblasts of asthmatics and controls. IL-4 has a dose–response effect on mRNA, with a maximal effect at 5 ng/mL, as determined by real-time PCR. The maximal increase in procollagen I (α1) was observed at 6 h after IL-4 stimulation in both BNF and BAF. BAFs have a greater increase in the procollagen I (α1)/β2 microglobulin ratio after 6 h of IL-4 stimulation (4.1×10−2±0.03 to 20.8×10−2±0.1) compared with BNF (2.9×10−2±0.006 to 9.2×10−2±0.08) (P=0.001). In transient transfection experiments, IL-4 increased promoter activity by threefold in BAF and BNF. Sp1 was up-regulated after IL-4 stimulation and AP-1 was down-regulated as shown by electrophoretic mobility shift assay. IL-4 decreased MMP-2 protein and mRNA levels, and did not alter TIMP-2 production.
Conclusions IL-4 positively regulates procollagen I (α1) transcription by direct promoter activation and increases the TIMP-2/MMP-2 ratio, thereby supporting the profibrotic effect of this cytokine. Thus, this study emphasizes that IL-4 may be considered as a link between inflammation and collagen deposition observed in asthmatic airways.