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Mutual inhibition by TGF-beta and IL-4 in cultured human bronchial epithelial cells
1Department of Internal Medicine, University of Nebraska Medical Center, Omaha 68198-5300, USA.
Insights
Transforming growth factor-beta (TGF-β) and interleukin-4 (IL-4) exhibit reciprocal inhibitory effects on airway epithelial cells, influencing inflammation and repair in conditions like asthma.
Area of Science:
- Immunology
- Cell Biology
- Respiratory Medicine
Background:
- Airway epithelial cells release cytokines and extracellular matrix components, contributing to immune responses, inflammation, and repair.
- Interleukin-4 (IL-4) has pro-inflammatory actions, while transforming growth factor-beta (TGF-β) is associated with repair and immune attenuation in airway diseases.
- Interactions between IL-4 and TGF-β are crucial in asthma, a disease involving inflammation and repair processes.
Purpose of the Study:
- To investigate the potential interaction between IL-4 and TGF-β in human bronchial epithelial cells (HBECs).
- To determine the effects of IL-4 and TGF-β on the release of IL-8 and fibronectin by HBECs.
Main Methods:
- Cultured human bronchial epithelial cells (HBECs) were treated with IL-4 and TGF-β.
- Release of IL-8 and fibronectin was measured.
- mRNA levels for IL-8 and fibronectin were analyzed.
Main Results:
- IL-4 induced IL-8 release from HBECs, an effect inhibited by TGF-β.
- TGF-β alone had a minor, inconsistent effect on IL-8 release and did not affect TNF-α-induced IL-8 release.
- TGF-β stimulated fibronectin release, which was inhibited by IL-4, suggesting reduced synthesis.
- Changes in cytokine and fibronectin release were mirrored by alterations in mRNA levels.
Conclusions:
- TGF-β and IL-4 exert mutually inhibitory effects on IL-8 and fibronectin release in airway epithelial cells.
- This reciprocal inhibition may be a key regulatory mechanism for inflammation and repair in airway diseases, including asthma.
Abstract:
The airway epithelial cell may play a role as an effector cell, releasing various cytokines and extracellular matrix components in immune responses, inflammation, and wound repair processes, thus contributing to cytokine "networks." The cytokines transforming growth factor (TGF)-beta and interleukin (IL)-4 are though to have pivotal roles in airway diseases, with IL-4 having proinflammatory actions and TGF-beta generally regarded to mediate repair and to attenuate immune responses. In asthma, where IL-4 and TGF-beta are thought to contribute to the inflammatory process and repair, respectively, interactions between these cytokines are likely to be of importance. Therefore, we studied the potential interaction of both cytokines by measuring IL-8 and fibronectin release by cultured human bronchial epithelial cells (HBECs). IL-4 is capable of inducing IL-8 release from HBECs. This effect of IL-4 can be blocked by the concurrent presence of the cytokine TGF-beta. In contrast, TGF-beta had a modest inconsistent stimulatory effect on IL-8 release by itself and had no effect on the IL-8 release induced by tumor necrosis factor (TNF)-alpha. An antagonistic effect of IL-4 and TGF-beta was also observed on HBEC fibronectin release. TGF-beta stimulated fibronectin release, and IL-4 was able to inhibit this. This effect was not due to a redistribution of fibronectin but appeared to be due to a true reduction in synthesis. Consistent with this, IL-4 and TGF-beta effects on IL-8 and fibronectin release were paralleled by changes in mRNA levels. The ability of TGF-beta to block IL-4-induced IL-8 release is certainly not the only mechanism to inhibit IL-8 release because dexamethasone was capable of inhibiting both TNF-alpha- and IL-4-induced release of IL-8. These results indicate that TGF-beta and IL-4 can have mutually inhibitory effects. The balance determined by this reciprocal inhibition may play an important role in regulating inflammation repair and in diseases such as asthma.